Class Reptilia includes many diverse species that are classified into four living clades.Reptilia includes four living clades: Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (turtles). These are the 25 species of Crocodilia, 2 species of Sphenodontia, approximately 9,200 Squamata species, and the Testudines, with about 325 species.
Crocodilia (“small lizard”) arose with a distinct lineage by the middle Triassic; extant species include alligators, crocodiles, and caimans. Crocodilians (Figure 1) live throughout the tropics and subtropics of Africa, South America, Southern Florida, Asia, and Australia. They are found in freshwater, saltwater, and brackish habitats, such as rivers and lakes, and spend most of their time in water. Some species are able to move on land due to their semi-erect posture.
Sphenodontia (“wedge tooth”) arose in the Mesozoic era and includes only one living genus, Tuatara, comprising two species that are found in New Zealand (Figure 2). Tuataras measure up to 80 centimeters and weigh about 1 kilogram. Although quite lizard-like in gross appearance, several unique features of the skull and jaws clearly define them and distinguish the group from the squamates.
Squamata (“scaly”) arose in the late Permian, and extant species include lizards and snakes. Both are found on all continents except Antarctica. Lizards and snakes are most closely related to tuataras, both groups having evolved from a lepidosaurian ancestor. Squamata is the largest extant clade of reptiles (Figure 3).
Most lizards differ from snakes by having four limbs, although these have been variously lost or significantly reduced in at least 60 lineages. Snakes lack eyelids and external ears, which are present in lizards. Lizard species range in size from chameleons and geckos, which are a few centimeters in length, to the Komodo dragon, which is about 3 meters in length. Most lizards are carnivorous, but some large species, such as iguanas, are herbivores.
Snakes are thought to have descended from either burrowing lizards or aquatic lizards over 100 million years ago (Figure 4). Snakes comprise about 3,000 species and are found on every continent except Antarctica. They range in size from 10 centimeter-long thread snakes to 10 meter-long pythons and anacondas. All snakes are carnivorous and eat small animals, birds, eggs, fish, and insects. The snake body form is so specialized that, in its general morphology, a “snake is a snake.” Their specializations all point to snakes having evolved to feed on relatively large prey (even though some current species have reversed this trend). Although variations exist, most snakes have a skull that is very flexible, involving eight rotational joints. They also differ from other squamates by having mandibles (lower jaws) without either bony or ligamentous attachment anteriorly. Having this connection via skin and muscle allows for great expansion of the gape and independent motion of the two sides—both advantages in swallowing big items.
Turtles are members of the clade Testudines (“having a shell”) (Figure 5). Turtles are characterized by a bony or cartilaginous shell. The shell consists of the ventral surface called the plastron and the dorsal surface called the carapace, which develops from the ribs. The plastron is made of scutes or plates; the scutes can be used to differentiate species of turtles. The two clades of turtles are most easily recognized by how they retract their necks. The dominant group, which includes all North American species, retracts its neck in a vertical S-curve. Turtles in the less speciose clade retract the neck with a horizontal curve.
Turtles arose approximately 200 million years ago, predating crocodiles, lizards, and snakes. Similar to other reptiles, turtles are ectotherms. They lay eggs on land, although many species live in or near water. None exhibit parental care. Turtles range in size from the speckled padloper tortoise at 8 centimeters (3.1 inches) to the leatherback sea turtle at 200 centimeters (over 6 feet). The term “turtle” is sometimes used to describe only those species of Testudines that live in the sea, with the terms “tortoise” and “terrapin” used to refer to species that live on land and in fresh water, respectively.
Full Title Name: Biological Information: Reptile Biology and Physiology
This overview describes the fundamental characteristics of reptile biology and physiology.
Reptiles Are Animals
Reptiles are animals, as are amphibians. Physiologically, they are similar and are sometimes collectively called “herpetofauna.” All of the excepted scientific classification systems regard reptiles as such. Under the two most common classification systems, reptiles are either grouped as the Class Reptilia or the Class Diapsida under the Kingdom Animalia, meaning “animals”. Moreover, under most legal definitions, reptiles are considered to be animals as well. For example, Connecticut defines an animal as including “birds, quadrupeds, reptiles and amphibians.” Con. Gen. Stat. §26-1(1) (2004). Wisconsin is equally specific: "’Animal’ includes every living: (a) Warm-blooded creature, except a human being (b) Reptile or (c) Amphibian.” Wis. Stat. §951.01 (2004). Florida, albeit in an unflattering way, also defines “animal” to include reptiles as “the word ‘animal’ shall be held to include every living dumb creature.” Fla. Stat. §828.02 (2005). An unsettling discrepancy lies in the Federal Government’s Animal Welfare Act. 7 U.S.C. §§2131 et seq. There, the “term ‘animal’ means any live or dead dog, cat, monkey (nonhuman primate mammal), guinea pig, hamster, rabbit, or such other warm-blooded animal, as the Secretary may determine is being used, or is intended for use, for research, testing, experimentation, or exhibition purposes, or as a pet” but excludes birds, mice, rats, horses and farm animals. 7 U.S.C. §2132(g). Conspicuously absent from the list are fish, amphibians and reptiles. Id.
Unfortunately, many people, unaware of the backings from science and the law, do not consider reptiles to be animals. In his article entitled “Herpetofauna Keeping By Secondary School Students: Causes For Concern”, David Bride complied the results of some alarming graduate studies that currently remain unpublished. See http://www.psyeta.org/sa/sa6.1/bride.html . His compilation refers to a study by Martin and Nicholls (Martin, D. & Nicholls, M. (1993). The importance of children's provenance in the understanding of "animal" - a comparison of town and village primary school children in Kent. Christ Church College, Canterbury: Ecology Research Group) of 400 five- to eleven-year-olds found between 10-40% of those surveyed did not recognize either snakes or frogs as animals. Similarly, Tinkler (Tinkler, D. (1993) Zoo visitors' perceptions of animals - and the short-term effect of a zoo visit upon them. Unpublished M.S. dissertation. University of Kent at Canterbury, DICE) recorded 60% of 150 adult zoo visitors failed to classify a lizard as an animal. From his investigation into unpublished studies, Bride hypothesized that this may be due to a confusion of term "mammal" with "animal." He recently found that of 228 respondents to a questionnaire about wildlife, at least 25% appeared to confuse the two. Bride found this view, that "animal" equals "mammal," to be interesting as it gives an entirely new perspective to what many people's interpretations of such concepts as "animal protection," "animal welfare," and "animal rights" may entail. See http://www.psyeta.org/sa/sa6.1/bride.html. Knowledge of what a reptile actually is may go far in soliciting the sympathy of the public.
A very common myth is that reptiles are “cold-blooded.” In addition to describing a general temperature of reptilian blood, the term also entails the negative connotations of evil and lifelessness. To be sure, in the Biblical story of Adam and Eve, it was a serpent that deceived mankind. However, reptiles are not “cold-blooded.” On occasion, they are quite the contrary and can even be “hot-blooded.” This gradation results in reptiles being “poikilothermic.” Poikilotherms have a body temperature that is variable with environmental conditions. If the ambient temperature is warm or even hot, that leads to a reptile having warm or hot blood. Another physiological term that accurately depicts reptiles is “ectothemy.” Ectotherms control the uptake of heat from the environment as a way to control internal body temperature. Reptiles are both poikilothermic and ectothemic, but are not cold-blooded. Moreover, some larger reptiles, such as large crocodilians, sea turtles and large monitor lizards approach a level of homeothermy. That is, their temperature does not fluctuate as much based upon the environment. This results from a physiology process known as gigantothermy, where a very large animal will maintain a constant body temperature with little input from the environment.
Another popular assumption is that since reptiles are “cold-blooded,” they therefore feel little or no pain. In fact, they have little physiological control over their internal body temperature and are instead almost completely reliant on external heat sources to provide them with enough warmth for their natural activities and for metabolic processes to operate. This makes these animals extremely sensitive even to subtle changes in temperature and humidity in their captive environment.
Added to the problems arising from their “cold-blooded” reputation, reptiles lack the repertoire of facial expressions and vocalizations that would alert keepers to their pain and distress. A sick, hurt, or chronically stressed reptile will typically suffer in silence. The suffering will often be far more prolonged than that experienced by mammals, due to reptiles' slow metabolic rate. Blood loss and the healing of injuries are both relatively slow, as are the consequent risk of infection and further complications.
Most reptiles have a preferred optimum temperature zone, a zone of temperature that they try to maintain while performing daily activities. Their entire physiology, including their immune defense mechanism, is temperature dependent and operates optimally at this optimal zone. Reptiles in captivity often are maintained at suboptimal temperatures, which results in a compromised immune system. Such animals are subject to infection by a great variety of secondary invaders, including the gram-negative microorganisms commonly isolated from their oral cavity. A reptile that is kept at its preferred optimum temperature (with all other environmental conditions being ideal) and receives proper nutrition is often a healthy reptile. For a more complete discussion of reptile physiology, see 18 Carl Gans & David Crews, Biology of the Reptilia, Physiology E, (1991). The cumulative effect of these common misconceptions may play a large factor in the cruel treatment and neglect of reptiles in captivity.
Evolution of Amniotes
Modern amniotes, which includes mammals, reptiles, and birds, evolved from an amphibian ancestor approximately 340 million years ago.
Outline the evolution of amniotes
- Synapsids include all mammals and therapsids, mammal-like reptiles, from which mammals evolved.
- Sauropsids, which are divided into the anapsids and diapsids, include reptiles and birds.
- The diapsids are divided into lepidosaurs (modern lizards, snakes, and tuataras) and archosaurs (modern crocodiles and alligators, pterosaurs, and dinosaurs).
- Skull structure and number of temporal fenestrae are the key differences between the synapsids, anapsids, and diapsids anapsids have no temporal fenestrae, synapsids have one, and diapsids have two.
- Turtle classification is still unclear, but based on molecular evidence, they are sometimes classified under diapsids.
- Although birds are considered distinct from reptiles, they evolved from a group of dinosaurs, so considering them separately from reptiles is not phylogenetically accurate.
- synapsid: animals that have one opening low in the skull roof behind each eye includes all living and extinct mammals and therapsids
- anapsid: amniote whose skull does not have openings near the temples includes extinct organisms
- diapsid: any of very many reptiles and birds that have a pair of openings in the skull behind each eye
- temporal fenestrae: post-orbital openings in the skull of some amniotes that allow muscles to expand and lengthen
Evolution of Amniotes
The first amniotes evolved from their amphibian ancestors approximately 340 million years ago during the Carboniferous period. The early amniotes diverged into two main lines soon after the first amniotes arose. The initial split was into synapsids and sauropsids. Synapsids include all mammals, including extinct mammalian species. Synapsids also include therapsids, which were mammal-like reptiles from which mammals evolved. Sauropsids include reptiles and birds and can be further divided into anapsids and diapsids. The key differences between the synapsids, anapsids, and diapsids are the structures of the skull and the number of temporal fenestrae behind each eye. Temporal fenestrae are post-orbital openings in the skull that allow muscles to expand and lengthen. Anapsids have no temporal fenestrae, synapsids have one, and diapsids have two. Anapsids include extinct organisms and may, based on anatomy, include turtles (Testudines), which have an anapsid-like skull with one opening. However, this is still controversial, and turtles are sometimes classified as diapsids based on molecular evidence. The diapsids include birds and all other living and extinct reptiles.
Tempral fenestrae: The image illustrates the differences in the skulls and temporal fenestrae of anapsids, synapsids, and diapsids. Anapsids have no openings, synapsids have one opening, and diapsids have two openings.
The diapsids diverged into two groups, the Archosauromorpha (“ancient lizard form”) and the Lepidosauromorpha (“scaly lizard form”) during the Mesozoic period. The lepidosaurs include modern lizards, snakes, and tuataras. The archosaurs include modern crocodiles and alligators, and the extinct pterosaurs (“winged lizard”) and dinosaurs (“terrible lizard”). Clade Dinosauria includes birds, which evolved from a branch of dinosaurs.
Evolution of amniotes: This chart shows the evolution of amniotes. The placement of Testudines (turtles) is currently still debated.
In the past, the most common division of amniotes has been into the classes Mammalia, Reptilia, and Aves. Birds are descended, however, from dinosaurs, so this classical scheme results in groups that are not true clades. Birds are considered as a group distinct from reptiles with the understanding that this does not completely reflect phylogenetic history and relationships.
Reptiles: Origin, History and Classification
Reptiles may be defined as “cold-blooded vertebrates, breathe by lungs throughout their existence, and having the body covered with scales or scutes. A basioccipital bone is present in the skull which articulates with the vertebral column by a single condyle” or Monocondylia with a scaly skin.
The first reptiles arose from ancient labyrinthodont amphibians during upper Carboniferous period, about 270 million years ago and have adapted to terrestrial life. Living orders can be traced back to the Triassic. More primitive forms still unquestionably reptiles are known from as early as the base of the Pennsylvanian.
History of Reptiles:
The term reptilia has originated from a Latin word “repere” which means ‘to creep’. The scientific study of reptiles dates back to the times of Aristotle and Pliny (400 B.C.). But afterwards there created a wide lacuna of about 2000 years in which nothing was done for the growth of knowledge on herpetology.
Again the methodological study on reptiles was started by Edward Tyson in 1683. John Roy (1693) placed amphibians and reptiles together under a single group. Though Brongniart (1800) pointed out some diffe­rences in some features between amphibians and reptiles (e.g., nature of the skin, reproduc­tion and embryonic development) but he also gave amphibians an order rank under Reptilia.
Various other workers like B. Merrem (1820), A. M. C. Dumeril and Bibron (1834-1854), T. H. Hexley (1864), Richard owen (1866), Boulenger (1855-1913), Cope (1890), Gadow (1901), Zittel (1908), Malcom A. Smith (1933-1943), Romer (1949, , ), Colbert (1951, , ), Coin and Coin (1962), Eric Worrel (1963), Bellairs (1970), L. M. Kianber (1972), Bellairs and Attridge (1975), Carl Gans (1969-), Coin and Zug (1978), and Benton (1997) have contributed much works on reptiles of the world.
Characteristic Features of Reptiles:
A. External Characters:
1. Skin dry, cornified, usually covered with epidermal scales or scutes. In some lizards, crocodiles and some dinosaurs, small plates of bone (osteoderms) develop in the dermis beneath the horny scales. Some amount of keratin, a water insoluble protein, is deposited in the epidermal cells that helps the skin to be dry and water­proofed.
2. The integumentary glands are a few scent glands that help to attract the opposite mates during breeding sea­son.
3. Two pairs pentadactyle limbs which end in clawed digits (absent in snakes and limbless lizards). Limbs paddle ­like in marine turtles and reduced in some lizards.
4. There is a single external nasal open­ing on the snout.
5. A post anal tail is usually present.
6. Ear drums are slightly depressed.
7. The cloacal opening is either trans­verse or longitudinal (chelonians and crocodilians).
B. Internal Characters:
1. A cloaca is always present and a well-marked division in between coprodaeum, urodaeum and proctodaeum.
2. Respiration is performed by lungs, affected by a backward movement of the ribs, produced by the intercostal muscles. Pharyngeal and cloacal respiration is seen in many aquatic turtles. Cutaneous respiration is seen in sea snakes by which they inhale up to 30% oxygen.
3. The heart is imperfectly 4-chambered and composed of two auricles and a ventricle, partly divided by a septum (ventricle completely divided in crocodiles). There are right and left systemic arches. Ductus caroticus and ductus arteriosus are often present. There is no truncus arteriosus. Three arterial trunks directly develop from the base of the ventricle.
4. The kidney of reptiles is of metanephric type. Each kidney is connec­ted with ureter for the removal of nitrogenous wastes of the blood. The large portion of the wastes is excreted. Sometimes an allantoic urinary blad­der is present.
5. Mullerian duct persists as oviduct in female and Wolffian duct is retained as vas deferens in male.
6. Central nervous system is better deve­loped in reptiles than amphibians. The cerebral hemispheres are enlarged by the presence of a mass of gray matter, the corpus striatum. Cerebral cortex is not developed in reptiles.
7. Twelve pairs of cranial nerves are present (except snakes). Snakes pos­sess ten pairs of cranial nerves.
8. Males possess copulatory organs except Sphenodon. Snakes and lizards possess paired hemispheres. Turtles and crocodiles have an unpaired penis.
9. Vomeronasal organ (Organ of Jacobson) is well-developed in most Squamatans and in Sphenodon.
1. Single occipital condyle in the skull.
2. Skull is provided with single or more temporal fossae except Anapsida where the fossae are absent. The fossae or holes in the temporal region are for the attachment of the temporal muscles.
3. Mandible consists of many pieces of bones (usually six bones).
4. Quadrate movable or immovable.
5. In the floor of skull, pterygoid and para-sphenoid are fused with basisphenoid.
6. Sternum is greatly developed with ribs and foramen.
7. T-shaped median interclavicle is present in the pectoral girdle.
8. Two sacral vertebrae instead of a single one in amphibians.
9. Vertebrae strongly procoelous in most reptiles.
10. The first two cervical vertebrae are modified into the atlas and axis. The first vertebra – atlas is a ring-shaped bone and without centrum.
11. The abdominal ribs or gastralia are dermal, jointed V-shaped rods found in the ventral body wall of spheno­don, lizards and crocodiles. These are not true ribs but are rib-like mem­brane bones (Kent and Miller, 1997).
12. The chevron bones are Y-shaped ossicles, attached to the caudal centra and representing the intercentra.
1. Most reptiles are oviparous, and a few species of lizards and snakes are viviparous.
2. The eggs are large, yolky and shelled (cleidoic egg). The calcareous shell serves for protection against desiccation and external injury. The shell is also porous that allows the gas exchange.
4. The embryos of reptiles are provided with chorion, amnion and allantois. The chorion and amnion develop as folds around the embryo. The chorion and amnion are a fluid filled sac-like structures where development of the embryos proceeds easily in the absence of pond.
The allantois is a sac-like out­growth from the junction of midgut and hindgut. The allantois is a highly vascularized organ that helps in respi­ration and its cavity participates in the excretion and storage of metabolites.
5. The large quantity of yolk in the yolk sac provides nourishment for the developing embryo during its embry­onic life. These embryonic features helped the reptiles, birds and mammals to be adapted for terrestrial reproduction.
1. Reptiles are ectothermic or heliothermic terrestrial vertebrates. Many zoo­logists incline to divide the vertebrates into poikilotherms (fishes, amphibians and reptiles) and homoiotherms (birds and mammals). Now herpetologists are in favour of ectotherms or heliotherms rather than poikilotherms for reptiles. The terms poikilotherms and homoiotherms are used to describe the rate of fluctuation of body tempe­rature.
In practice, some reptiles live in a stable environment and have a stable body temperature. But they cannot maintain a temperature above the surroundings generating within the body. They become dormant in below temperature and die in high temperature.
So for this complexity it is difficult to use poikilotherms. The ectotherms and endotherms are not synonymous with the poikilotherms and homoiotherms respectively, because instead of temperature regu­lation they mean the source of energy for temperature regulation.
Ectotherms or heliotherms (Gk. helios, sun) depend totally on solar energy either directly or indirectly (e.g., by con­duction from warm ground) for temperature regulation.
Reptiles bask in the sun at the cold days and take shelter in crevices and holes or lies parallel to the sun rays when body temperature rises very high. Endotherms derive energy from metabolism for temperature regu­lation. Like mammals, the body tem­perature of reptiles is regulated by a centre of hypothalamus of the brain.
Classification of Reptiles:
Subclass 1. Anapsida [without an arch] [Gk. an = without apsis = an arch]
1. This subclass is characterised by the skull devoid of fossae in the temporal region.
2. The roof of the skull is solid.
This subclass includes three orders: Cotylosauria, Mesosauria and Chelonia.
Order 1. Cotylosauria (Garb.—Per.) [Gk. kotye = cup shaped hollow sauros = lizard]
All the members of the order are extinct and possibly form the ‘stem reptiles’ from which other reptiles have probably been evolved. They lived between Upper Carboniferous to Upper Triassic periods.
The characteristic features are:
1. The complete roofing of the skull.
2. Flattened plate-like pelvis.
The order includes two suborders: Captorhinomorpha and Diadectomorpha.
The earliest known fossil cotylosaur is Romeriscus, collected from the lower Pennsylvania. The well-known Cotylosaurs are Romeriscus, Limnoscelis, Captorhinus, Labidosaurus, Seymouria and Diadectes (Fig. 8.42).
(i) They occur in late Carboniferous or early Permian strata,
(ii) They were aquatic in habit and lived in freshwater lakes.
(iii) The body was slender and measured not more than a metre in length,
(iv) The skull was devoid of temporal fenestrae.
(v) The hind legs were much powerful than the front legs. Both the limbs were paddle-shaped.
(vi) The tail was long and laterally com­pressed, used for swimming.
Order 3. Chelonia (Testudinata) (Per.— Re.) [Tortoise and Turtles [Gk. Chelone = a tortoise L. testudines genitive of Testudo = a tortoise] [About 230 species]
Chelonians are assumed to be direct descendants of primitive cotylosaurs. In the evolutionary history of reptiles, the develop­ment of a box-like exoskeleton appears extremely peculiar. This bizarre armour remained unaltered since Triassic period (about 215 million years back).
The characte­ristic features of the chelonians are:
1. The body is more or less elliptical and dorsoventrally flattened.
2. Body is encased by a convex dorsal shield, called carapace and a flat ventral plate designated as plastron which remains, joined at sides.
3. Neck, limbs and tail are retractile into the carapace in most non-marine forms.
4. Limbs are weak, pentadactyle and modi­fied into paddle in marine forms. In aqua­tic (ponds, lakes and rivers) forms the limbs are webbed. The chelonians walk slowly on land but swim fastly by the pad­dles in marine forms.
Normally, the fore limb has five well- developed claw bearing digits, while the hind limb has four well-developed claw bearing digits and a fifth clawless digit. In the leather back, Dermochelys claws are totally absent.
Different tortoises walk on different parts of the limb. Plantigrade gait is seen in Geochelone, digitigrade in African hinge-back tortoise, Kinixys, or unguligrade is seen in the burrowing tor­toises like Gopherus. The terrestrial forms possess stumpy feet.
5. Body shell is externally protected either with polygonal scutes or leathery scales.
7. The cloacal opening is oval or longitudi­nal.
8. Male possesses a single grooved copula- tory organ.
9. Teeth are absent in adult condition and the jaws are covered by sharp horny plates in recent forms. Eunotosaurus, a mid-Permian fossil had teeth. They are either herbivorous or carnivorous. The terrestrial forms are always herbivorous but aquatic forms are either herbivorous or carnivorous.
10. The large intestine is divided into caecum, colon and rectum. The rectum enters the cloaca (Fig. 8.43).
11. The heart consists of a muscular sinus venosus, two thin-walled auricles and a thick-walled, conical, partly divided ventricle (Fig. 8.44). The ductus arteriosus (ductus Botalli) persists in some chelo­nians. The main aortae arise from the base of ventricle.
(ii) Left systemic arch and
(iii) the Brachiocephalic arch from which the right systemic arch originates.
The pul­monary arch divides to form Pulmonary arteries carrying blood to the lungs.
The left systemic arch gives three arterial branches:
(ii) Pancrea­ticoduodenal artery and
(iii) Superior mesenteric artery (Fig. 8.45).
12. The venous system is typically reptilian. It includes two anterior precaval and one postcaval veins. Both renal and hepatic veins are present. Fig. 8.46 shows the venous system of a turtle.
13. Lungs are spongy sacs, attached to the inner surface of the shell and are invested with peritoneum on the ventral side only (Fig. 8.47). Breathing is brought about by the contraction of the abdominal muscles. Cloacal respiration performs in some aquatic forms (e.g., Emys) by drawing water into special vascularized diverticuli of the urodaeum.
Pharyngeal respiration is seen in soft shell turtles. The fringe-like processes of the pharynx are thought to be used during respiration in submerged condition. The metabolism of chelonians is very low and can suspend breathing for a considerable period. Some turtles can stay underwater several hours and at the moment they derive energy by anaerobic glycolysis.
Most vertebrates cannot tolerate the pre­sence of excessive carbon-dioxide (CO2) either in lungs or in blood. But the turtles have overcome this problem by evolving certain physiological mechanisms. When higher CO2 is present the acidity in the blood increases and pH level is decreased.
Turtles have developed a mechanism to buffer the blood with bicar­bonate ions, haemoglobin and serum pro­teins which resist the pH change so that they can tolerate a higher CO2 per unit volume than in other vertebrates.
14. Kidney is metanephric type. It includes two flattened and lobed kidneys, ureters and urinary bladder (Fig. 8.48). Nitro­genous waste material contains urea and uric acid.
The reabsorption of water in the cloacal region helps to form a whitish paste-like excretory product. Bilobed urinary bladder (allantoic) is present on each side of the cloaca in male chelo­nians and in most cases an accessory urinary bladder is present on either side of cloaca.
15. The cerebral hemispheres are well-deve­loped with large basal regions (striatum) and pallium.
16. Oviparous. Chelonians lay hard-shelled round, oval or elliptical white eggs. The terrestrial forms lay in the holes, dug by them on land. The marine forms lay their eggs in holes on the sandy beach, scoo­ping away the sand by hind feet.
17. In temperate regions, all chelonians hibernate regularly.
18. Skull is anapsid type (Fig. 8.49). All skull bones are firmly united to each other.
19. Quadrate is immovably articulated with the skull (monimostylic).
20. Single, median nasal opening. No distinct nasal bones, their places are taken by pre­-frontals.
21. The inter-parietal foramen is lacking.
22. The palatines are well developed which unite with the median vomer to form a hard secondary palate separating the nasal cavity from the mouth cavity.
23. Supraoccipital crest is large and well developed.
24. A long sagittal crest (e.g., Trionyx) is pre­sent in many species.
25. Epipterygoids are sometimes small or none.
26. Lacrimal, septomaxilla or ectopterygoid are rudimentary or absent.
27. A pseudo-temporal fossa is found in some freshwater chelonians which has the same function as the true temporal fossa.
28. Thoracic vertebrae and ribs are usually fused with the carapace.
29. Ribs contain capitular portion only.
30. Two sacral vertebrae are present.
31. Pectoral girdle consists of a scapula attached to the carapace dorsally and earing near the base a long pro-coracoid, and a backwardly directed coracoid.
32. The pelvic girdle consists dorsally placed ilia attached to carapace and ischia and pubis are broad. Pubes and ischia form symphyses. An epipubic cartilage is present.
33. The caudal vertebrae are typically procoelous and freely movable. They bear rudimentary ribs.
34. The abdominal ribs are absent and the cervical ribs are rudiment
Origin of Chelonians:
The origin of chelonians is still obscure. Palaeontological history started from Triassic about 215 million years ago, but undoubtedly must have originated even earlier in Permian from cotylosaurian ancestors. Proganochelys of Late Triassic is considered the ancestor of che­lonians.
Eunotosaurus is con­sidered a missing link between the chelonians and cotylosaurs and a small reptile of which an incomplete skeleton was preserved and col­lected from the Middle Permian of South Africa. The trunk was short and broad like those of a turtle.
The ribs which are 8 in num­ber are broad and flat like those of a turtle. The roof of the skull is damaged, so it is not possi­ble that they are anapsid or not. They pos­sessed teeth, but had neither carapace nor plas­tron. From the above characters it differs from the chelonians and it is assumed that the cara­pace and plastron were a later acquisition.
Although, Eonotosaurus africanus is believed for long as a missing link between the Testudines and Cotylosaurian rep­tiles, the recent opinion is that Eonotosaurus may be a side line species.
Number of genera and species:
About 318 species under 74 genera have been recorded from the different parts of the world in which 9 species under Testudinidae have become recently extinct. From India 32 species under 16 genera have been recorded. Pascoe (1973) listed about 18 fossil turtles from India, Pakistan and Burma (Myanmar).
They are found in terrestrial, aquatic (ponds, lakes, marshes, reservoirs, estuaries and rivers) and marine environments.
Carnivorous forms consume a large num­ber of invertebrates, such as earthworms, crabs, insects, insect larvae, snails and bivalve molluscs. Larger forms eat fishes, frogs and birds. Herbivorous forms choose aquatic plants as food.
The life span of the turtles are longer than other vertebrates. The average life span of the turtle in the wild is between 25 to 50 years. The record in captivity is far greater than the wild condition. Aldabra giant tortoise, Geochelone gigas, which had been exhibited in the Calcutta Zoo Garden since 1875, died in 2005. Before that it was in the garden of Governor General at Barrackpur.
At the time of death it was over 200 years old. The Royal Tongan tortoise Testudo radiata, presented to the then king of Tonga (Island of Pacific ocean) by captain James Cook (1720-1779) on October 22, 1773, died on 19th May, 1966, survived about 200 years.
According to New Encyclopaedia Britanica (1973), the aquatic genus in U.S.A., Gopherus, has a speed of 0.21-0.48 km/hr. The aquatic species, Pseudemys floridana, was recorded at 1.7 km/hr, and the marine green turtle, Chelone mydas, can swim 480 km in 10 days.
Generally the chelonians are thought to be dull animals. But some turtles like aquatic forms, such as the snapping turtle (Chelydra) and alligator turtles (Macroclemys) show some skill in capturing fish and birds as food.
Visual, tactile and olfactory signals are used among turtles during courtship. Tortoises pro­duce various vocal sounds before mating. The sounds are described as grunts, bellows and moans. During breeding season, glands of some species are enlarged and produce pheromones.
Pheromones help to identify opposite sexes of particular species. Before mating, the males of some species sniff the cloacal region of the females and trail females at day time. Faecal pellets are the territorial markers among the males of a particular species.
Among the turtles, colour pattern on the body, specially on head, neck and limbs help the males to identify the females of the same species. Pheromones play a vital role in the identification of the species. Some long clawed males swim in front of the females, vibrating his claws on the side of the female’s head during courtship.
Biting, ramming and hooking are used by tortoise males as tactile signals against females before mating.
Artificial female production:
Scientists at the University of Texas, Austin have reported that applying a drop of com­mercially produced Oestrogen, a sex hor­mone, to a developing egg, results in a female embryo. The oestrogen dissolved in alcohol and absorbed through the egg shell proved a simple method to ensure female embryos. It has been applied on the eggs of fresh water turtles, lizards and alligators and have obtained female embryos.
Structure of Shell:
The shell consists of dorsal carapace and ventral plastron and lateral bridges. The cara­pace is the upper part of the shell which covers the back and sides, plastron covers the belly and both of them are joined on each side by the bridge.
The carapace develops from the bony plates in the dermis which may be attached to some endo-skeletal parts. The carapace is con­stituted of several plates (Fig. 8.50A) which are arranged in a regular fashion. Leaving aside minor variations, the carapace is made up of a median row of neural plates. There are usually eight such neural plates.
These plates are fused with the spinous processes of second to ninth thoracic vertebrae. There is a large median nuchal plate joining with the first neu­ral plate which remains attached to the neural spine of the eighth cervical vertebra.
Behind the eighth neural plate lie three pygal plates. The first two pygal plates are united with the eighth costal plates while the third one joins with the posterior marginal plate. Eight pairs of large rectangular costal plates, four pairs on each side, are present.
The costal plates are transversely arranged and are fused with the ribs of second to eighth thoracic vertebrae. The ribs project beyond the outer margin of costal plates and each rib ends in one of the marginal plates which form the boundary of the carapace. There are usually eleven pairs and an unpaired posteromedian marginal plate.
The first marginal plate is attached to the side of the nuchal plate, while the last one occupies a median position to join with the last pygal plate. The nuchal, pygal and marginal plates are considered to be exclu­sively endodermal derivatives while the neural and costal plates are regarded to the expan­sions of endo-skeletal structures.
The plastron remains attached directly or by ligament to the marginal plates of carapace. It consists of dermal bones. In turtle, the plas­tron consists of nine pieces : one entoplastron and four paired pieces—epiplastra, hyoplastra, hypoplastra and xiphiplastra (Fig. 8.50C).
The entoplastron is supposed to correspond to the interclavicle and the epiplastra correspond to clavicles of other forms. In most chelonia, the pieces of plastron remain in close contact by their margins to form a continuous plate.
Both the carapace and plastron are cov­ered externally by horny epidermal shields formed by the cornifications of the outer parts of epidermis. Cornification is continuous throughout life and the horny plates increase both in area and thickness. The horny shields are regularly arranged on the surface of cara­pace as well as plastron.
The dorsal surface of carapace has a median row of five vertebral shields, two lateral rows of four costal shields and a marginal row of twenty-four or twenty- five marginal shields. Of the marginal shields, the anteromedian one is called nuchal shield and the posterior one is designated as pygal or supra-caudal shield.
The plastron is covered by six pairs of shields, called the gular, humeral, abdominal, femoral and anal shields (Fig. 8.50). Besides, one or two integular shields are present in front of gular shields. Five or six infra-marginal shields are present on the ventral surface to the marginal shields of the carapace.
The tortoise, terrapin and turtles show many distinguishing features which are given in the Table 32.
Modern living chelonians are divided into two suborders:
1. Pleurodira (side-neck tur­tles) and
2. Cryptodira (hidden-neck turtles). (Fig. 8.51 shows various types tortoises, terrapins and turtles).
Suborder 1. Pleurodira (Side-neck turtles)
[Gk. pleuro = side, dire = neck]
They are more primitive and surviving from the Mesozoic era. They generally curve the neck and draw the head sideways under the shell and are confined to the southern conti­nents.
Family 1. Pelomedusidae (Fresh water terra­pins) of Africa, Madagascar and Southern Australia.
Neck is completely retractile under the shell and head is covered with horny shields.
Family 2. Chelyidae (Snake necked turtles) of South America, Australia and New Zealand.
Head and neck not completely retractile under the shell.
Matamata (Chelys fimbriata, Fig. 8.51 A) found in the rivers of Brazil, Venezuela and the Guianas, Australian snake-necked turtle (Chelodina longicollis, Fig. 8.51 B).
Syborder 2. Cryptodira (Hidden-neck turtles)
They are almost cosmopolitan in distri­bution and are found since Cretaceous. Head is withdrawn by the ‘S’-shaped fashion of the neck.
They include the following fami­lies:
Family 1. Dermatemyidae (Mexico and Central America):
Family 2. Platysternidae (Fresh water forms of Southern Asia).
Head large and tail long hooked mandible.
Family 3. Chelydridae (Snapping turtles) of North and Central America.
Head and neck large, cannot be withdrawn under shell long tails upper jaw hooked.
American common snapping turtle (Chelydra serpentina) and Alligator snapping turtle (Macrochelys temmincki, Fig. 8.51 C).
Family 4. Emydidae (Freshwater tortoises of almost cosmopolitan in distribution except Australia, Central & Southern South America):
Head covered with smooth skin complete­ly retractile neck digits webbed.
European pond tortoise (Emys orbi­cularis), Diamond back terrapin (Malaclemys terrapin) of United States, River turtles of Nor­thern India (Kachuga kachuga), Spotted pond turtle of Ganges and Indus river (Geoclemys hamiltoni), Batagur baska (Assam, Bengal).
Family 5. Testudinidae (Land tortoises) of Cosmopolitan distribution except Australia and Polynesia.
Domed shells short, broad feet and web-less digits.
Indian star tortoise (Ceochelone elegans, Fig. 8.51 D) Spur thighed tortoise (Testudo gracea) of Spain, Asia Minor, Coastal region of Mediterranean sea Giant Tortoise of Aldabras (T. gigantea) Galapagos tortoise (Ielephantopus), etc.
Family 6. Trionychidae (Soft shelled turtles) of Asia, Africa and North America:
Soft proboscis, fleshy lips, carapace cov­ered with smooth skin and digits with 3 claws.
Indian soft-shelled turtle (Trionyx gangeticus, Fig. 8.51 E), Indian flap-shell turtle (Lissemys punctata), Painted turtles (Chrysemys) of Atlantic coast to Eastern Washington.
Family 7. Chelonidae (Sea turtles):
Limbs flipper like and clawed shell covered with smooth horny shields.
Green turtle (chelonia mydas), Logger head (Caretta, Fig. 8.51 F) of Atlantic coast and Hawkbill turtle (Eretmochelys), etc.
Family 8. Dermochelyidae (Leatherback sea turtle):
Limbs flipper-like and clawless Shell covered with smooth skin.
Leather back turtle (Dermo­chelys coriacea, Fig. 8.51 G)
Family 9. Carettochelyidae:
Limbs paddle-shaped shell soft.
Five of the world’s seven species of sea turtles are found around the different shores of Indian sub-continent. Six of the world’s seven species of sea turtles are listed in the IUCN Red Data Book of threatened or endan­gered.
At present all the five species of Indian sea turtles are placed under Schedule 1 of the Indian Wild life (Protection) Act, 1972 which accords total protection. Four species—the Olive Ridley, the Leatherback, the Hawkbill and the Green turtles were once abundant in Indian waters now all except the Olive Ridley are rare.
Olive Ridley (Lepidochelys olivacea (Esch- scholtz, 1829) [Family Cheloniidae]
The Olive Ridley is India’s commonest and smallest sea turtle. It is recognised by uni­formly greyish colour in the adult. Gahirmatha and also Devi estuary in Orissa, provide largest concentrations of sea turtles in the world. During breeding season they are seen at the Digha (West Bengal) beaches. They nest on both coasts of India, also in Lakshadweep, and on the Andaman and Nicobar Islands.
During breeding season, from November to March, the females reach on the sandy beaches, dig holes about 55 cm deep and after laying they close the holes with sand, and gradually depart the beaches. They spend on the beaches between 50 to 150 minutes for egg laying. About 1 million Ridley mothers lay about 50 million eggs.
Besides Gahirmatha, the world’s other Olive Ridley’s sand tookeriars are in the coasts of Oaxaca, Mexico and Guanacaste, Costa Rica. At Nancite beach, Costa Rica (Fig. 8.52) the Olive Ridleys enjoy excellent pro­tection within Santa Roas National Park. The Mexican turtles which once represented the largest concentration of sea turtles in the world, have been severely depleted.
It is believed that numerous sea turtles are abundant in the eastern part of the pacific ocean. At a few places they congregate in unusually large numbers and emerge during three to seven day periods. The synchronous nesting behaviour, called Arribadas in Latin America, has been described as mass activity of the animal kingdom.
Hawkbill Turtle, Eretmochelys imbricata imbricata [Family Cheloniidae]
It is one of the smallest sea turtles. It is found in scattered numbers on breeding and feeding grounds. They are found to live among the coral reefs and rocks in Lakshadweep, on the coasts of southern India and in Andaman and Nicobar Islands.
They also visit Digha sandy beach during breeding season. They are recognised by bird-like beak and two claws on the front flippers. They con­sume sponges, crabs and molluscs. The Hawkbill often eats creatures that are poi­sonous to man.
Mating takes place from July to August and egg laying from September to February. The incubation period ranges from 45-60 days.
Green Turtle, Chelonia mydas agassizii.
It is recognised by unhooked beak and a single clawed flippers. It is also named by greenish colouration of the dorsal and yel­lowish ventral. They are mainly found on the Gujarat coasts, and also some members on the remote islands in Lakshadweep and the Andaman and Nicobar Islands.
Thousands of Green turtles are consumed annually in Southern India. Around Krusadai Island, near Rameswaram Island, South India, they are abundant in number. They subsist on the abundant sea grass and algae.
They lay about 100 eggs and leave them buried in the sand. After 60 days, the baby turtles hatch out and start in groups towards sea. Across the open sandy beach, death awaits by the predator crabs, gulls and herons.
Loggerhead Turtle, Caretta caretta gigas [Family cheloniidae]
It is identified by brownish colour and complete ossified carapace.
It is the largest member of the family cheioniidae. The adult turtle’s weight reaches about 400 kg. It is mainly found around Sri Lanka’s coasts. In our waters, it is found in the Gulf of Manner, near Sri Lanka. The nests are not found in our shores.
Mating takes place before the nesting season. Oviposition is seen from January to February. The incubation period ranges 50 to 65 days.
They feed on molluscs, crustaceans, fish and jelly fish.
Leatherback Turtle, Dermochelys coriacea schlegelii [Family Dermochelidae]
The Leatherback or the Leathery turtles is called for its thick, leathery tissue on its cara­pace. This is the largest turtle among the marine turtles. Its weight is above 600 kilo­grams and lengths of more than 2 metres. It is recognised by clawless limbs, seven promi­nent ridges along the dorsal side and dark brown colour in adult. Due to heavy poach­ing for its meat and -eggs, they have disap­peared from India’s mainland beaches.
They lay eggs in remote areas in Little Andaman, Great Nicobar and Katchall of Andaman and Nicobar Islands. Recently it is seen to visit the coasts of Kerala frequently. About 10-15 years ago, the author (6th edition) has seen the dead body at Digha coast.
Generally it is found in the tropics but its distribution has recorded far and wide than other turtles. It can penetrate cool temperate areas and have been recorded in the Atlantic and Pacific oceans. They feed on generally jelly fishes. Leatherback turtles can dive more than 1000 metres below.
The conservation of sea turtles in our country is a complex matter because the species ranges over thousand miles and the breeding sites around the Indian main coastal lines are being disturbed by the tourist com­plexes.
Otherwise the turtle nesting popula­tions have been subjected to heavy exploita­tion for meat, eggs, shell and leather, and have suffered high levels of mortality from incidental catch by fish and shrimp trawlers. In our country, no sufficient work has done on artificial breeding.
Our Government, some private agencies, and dedicated persons are endeavoring to stop the catching and illegal poaching in different breeding site areas. Once 30000 Olive Ridleys would reach annually in Calcutta markets from Orissa, Andhra and West Bengal for sale, now that has stopped more or less.
Artificial captive breeding of turtles in the Research Station is being successful gradually. The Charles Darwin Research Station on Santa Cruz Island, Galapagos Archipelago have become successful on Geochelone nigra hoodensis and Ceochelone guntheri.
From 1978-1986 the Mexican Institute National de Pesca, in collaboration with U.S. Fish and Welfare Service and the National Marine Fisheries Services has become suc­cessful in Kemp’s ridley (Lepidochelys kempi).
Subclass 2. Synaptosauria (= Euryapsida) [Gk. synaptas = joined]
Colbert (1945) suggested the term Eury­apsida instead of Synaptosauria but Romer (1956, 1962) continued to use the term Synaptosauria.
(i) Late Palaeozoic and Mesozoic aqua­tic reptiles are included under the subclass.
(ii) They possessed a single temporal (parapsid) fossa high in the skull. Synaptosauria includes three orders: Protorosauria, Sauropterygia and placodontia.
Order 1. Protorosauria (Per.—Tri.):
(i) Existed during lower Permian.
(ii) The reptiles were lizard-like in appea­rance, not exceeding 30 cm in length.
(iii) They were terrestrial and were very agile.
(iv) The vertebrae were amphicoelous.
Order 2. Sauropterygia (Tri.—Cre.) [Gk. sauros = lizard pterygos = fin]:
(i) Existed between Permian and Triassic strata.
(ii) They were aquatic in habit. They had sin­gle temporal vacuity in skull which were bounded below by a postorbital.
(iii) The squamosal and coracoid were sin­gle.
(iv) The feet were webbed in some forms.
Cyamodus, Plesiosaurus (Fig. 8.54), Elasmosaurus (Fig. 8.55).
Order 3. Placodontia (Triassic):
More or less related to the plesiosaurs and had grinding teeth on jaws and palate. Example:
Placodus (Fig. 8.53A), Henodus (Fig. 8.53B).
Subclass 3. Ichthyopterygia [Gk. ichthys = fish pterygos = fin]
(i) The members are all extinct.
(ii) The roof of the skull was provided with an upper opening behind the eye and was bound below by postfrontal and supra-temporal.
Order 1. Ichthyosauridae (Tri.—Cre.):
(i) They occurred between middle Triassic and upper Cretaceous.
(ii) They were marine and fish-like in appearance. Some were of considerable length measuring about 10-15 metres.
(iii) Their skull had a single lateral vacuity.
(iv) The head was large and produced into an elongated snout.
(v) The tail was long and limbs were in the form of paddles.
(vi) The vertebrae were amphicoelous and cervical ribs were double-headed.
(vii) The sternum was lacking but abdominal ribs were present.
Ichthyosaurus, Ophthalmosaurus (Fig. 8.53C).
Subclass 4. Lepidosauria [Gk. lepis = scale sauros = lizard]:
(i) Representatives of this subclass have two temporal vacuities in the skull.
(ii) In some specialised forms the vacuities have become reduced.
Lepidosaurs are the sister lineage of archosaurs and both groups (lepidosaurs and archosaurs) have evolved independently from the cotylosauria.
This subclass embraces three orders: Eusuchia, Rhynchocephalia and Squamata.
Order 1. Eusuchia (Up. Carb.—Eo.):
(i) Lived in the upper Permian period.
(ii) The skull had inter-parietal and tubular bones and parietal foramen.
(iii) An orbital foramen, was absent.
They are considered as the ancestors of all modern lepidosaurs.
Order 2. Rhynchocephalia (Tri.—Re.) [Gk. rhynchos = a beak, snout kephale = a head] Beaked upper jaw 2 species.
The order Rhynchocephalia is represented by two living representatives, Sphenodon punctatums and S. guntheri. The group is known from the middle Triassic (e.g., Rhynchosaurus, Fig. 8.53D) of Asia, Africa, Europe and America. Sphenodon is the oldest surviving lepidosaurian reptile and a Mesozoic fossil (Homoeosaurus) shows the continuity of the race. It is a living fossil and is popularly called the ‘Hatteria’ or ‘Tuatara’.
1. Sphenodon (Fig. 8.56A) has a lizard-like body measuring about 70 cm in length. There is a overhanging beak on the upper jaw.
2. The body is dull olive green in colour with yellow spots above and whitish below.
4. The tail is bilaterally compressed and crested. The tail can regenerate, if it is lost.
5. Except the lower side where the scales form transverse rows of large square plates, the body is covered by small granular scales.
6. A median row of erective spines (frill) extends from the top of the head to the tip of the tail, but is interrupted at the neck region (Fig. 8.56A).
7. The eyes are large, dark-brown in colour with vertical pupil.
8. The cloacal aperture is a transverse slit.
9. The males lack copulatory organs (Primi­tive feature).
10. The skull is typically built on the lepidosaurian plan (diapsida primitive feature).
11. The skull is composed of paired premaxillae, nasals, frontals and parietals (Fig. 8.56B, C).
12. A parietal foramen is present.
13. Three temporal fossae are present.
(a) supra-temporal, situated behind the orbital fossa,
(b) infra-orbital, located lateral to the supra-temporal and
(c) post- temporal, bound by post-temporal bar.
14. A fenestrated inter-orbital septum is pre­sent.
15. Quadratojugal is ossified and quadrate is united to pterygoid, squamosal and quadratojugal.
16. A vacuity is present between the median part of the pterygoids.
17. An epipterygoid (The bone connecting pterygoid and parietal) is present.
18. The rami of the lower jaw are united by ligament.
19. The vertebrae have amphicoelous centra (Fig. 8.56E) with intercentra and persis­tent notochord (Primitive feature).
20. A so-called pro-atlas is present.
21. Almost all the vertebrae possess chevron bone.
22. The caudal vertebrae are divided by septum.
23. The ribs are single headed, some of the ribs bear more cartilaginous uncinate processes.
24. First three ribs are represented by bands of connective tissue. Other ribs are bony. Abdominal ribs are present (Primitive feature).
25. A median sternum is present.
26. The pectoral girdle consists of the clavi­cles either side of which joined with a median interclavicle. Besides these three dermal elements, the chondral elements of either side include a scapula which remains fused with a ventromedial pro-coracoid (Fig. 8.57A).
27. The scapula has a process like the acromion process in Sphenodon extended to the clavicle.
28. A cartilaginous suprascapula is present above the scapula. The suprascapula may possess a clavicular process.
29. The humerus bears both an ectepicondylar and an entepicondylar foramina.
30. There are 10 or 11 pieces of separate carpal bones.
31. The pubes are united by a symphysis. A cartilaginous epipubis is present.
32. A large ischiopubic foramen is present between the ischium and pubis. A carti­laginous hypo-ischium is fixed to the ischia behind.
33. The ilia are blade-like and are nearly ver­tically disposed (Fig. 8.57B).
34. In Rhynchocephalia, the teeth are acrodont and are fused with the subse­quent bone (primitive feature).
35. A row of small triangular teeth is present on the maxilla and another set on the palatine. The mandibular teeth bite between the two rows on the upper jaw.
36. The pterygoids are toothless. Vomerine teeth are present in young individuals. In adults, such teeth are replaced by pads.
37. The heart is typically reptilian, but the three main arches instead of emerging independently from the ventricle, come off by a short common trunk (primitive feature). The arterial and venous systems show certain interesting points of simi­larity with that of urodela.
38. The brain is simple (Fig. 8.58A) with a very well-developed parietal organ (third eye) or Pineal eye (primitive feature).
39. Much publicity has been given to the so- called third eye of Sphenodon. In young stage, its position is marked by a translu­cent scale over the skull. But in the adult, it becomes covered with skin. The third eye is made up of a lens, a retina with a rierve connected to the brain, but iris is absent (Fig. 8.58B). The third eye (Perietal organ) does not form retinal image. It can monitor the duration of environmental photoperiods and internal biological rhythms. It can also monitor the intensity of solar radiation.
Till now the single species—Sphenodon punctatus (= Hatteria punctata) was known to pineal body cerebellum medulla parieial organ optic lobe Wongata the zoologists. In 1990, another species, Sphe­nodon guntheri, which was described in 1877, recovered from North Brother Island of New Zealand.
The only surviving population— S. guntheri includes about 300 individuals. Sphenodon is known as Tuatara. Tuatara is a ‘Maori word’. Maori is a tribe of New Zealand. Tuatara populations occur on about 20 islands off the coast of New Zealand.
Habit and Habitat:
Terrestrial, nocturnal, sluggish in habits, living in burrows in soft soil in the day time. It lives with various kinds of petrols on amicable manner in its burrows. It cannot tolerate other animals, even other members of its own species.
They cannot raise their body tempe­ratures by basking in the sum, as most reptiles do. Body temperatures are reported to be near 11 °C for active tuataras and are extremely low for reptiles (McFariand et al., 1985). They feed mainly on insects with an occa­sional gecko or baby sea bird. The life process of Sphenodon is slower than that on other rep­tiles and the eggs take more than a year to hatch. They attain sexual maturity at the age of 20.
Once Sphenodon was wide­spread in the main islands of New Zealand but is now restricted to some islets in the Bay of Plenty, North Islands. Due to attacks of wild pigs, dogs, cats, reptile-eating Maori tribes, the remaining members of the genus, Sphenodon, have now taken the shelter in some small islands. Very recently rigid conservative mea­sures have allowed the genus to recover in number to a considerable extent.
Members of this order (Homoeosaurus, Rhynchosaurus) were relatively com­mon during Mesozoic times (Middle Triassic) on many parts of the world (Africa, America, Europe and Asia).
Rate of evolution:
Creatures like them were recorded in the late Triassic, so they are of the slowest rates of evolution.
Biological status of Sphenodon:
Sphenodon possesses many peculiar fea­tures. It shows many structural similarities with the lizards.
(1) Presence of parietal organ.
(2) Similar circulatory and respiratory systems.
(3) The skull is typically built on the lacertilian plan.
(4) Amphicoelous vertebrae in Sphenodon and Gecko.
But Sphenodon differs from the lizards by having:
(1) An extra vacuity in the skull,
(3) Abdominal ribs and uncinate pro­cess,
(4) Ectepicondylar and entepicondylar foramina in the humerus and
Sphenodon is undoubtedly a primitive and generalized type of reptile. That it is a rep­tile is clear from the study of its anatomical features but regarding its systematic position scientists like Gadow, Baur, Gunther, Sedgwick, Huxley and many others differ in their opinions.
Following is a discussion on its affinities with other groups of reptiles both living and extinct.
(1) Skull is of diapsid type and the quadrate is fixed.
(2) Presence of unci­nate process and abdominal ribs.
(1) Ribs are single- headed in Sphenodon but they are double- headed in Dinosaurs.
(2) The teeth in Sphenodon are acrodont, while they are the­codont in Dinosaurs. (3) Clavicle, interclavicle and parietal organs are present in Sphenodon but these are absent in Dinosaurs.
The Rhynchocephalia together with Protosauria to which they are closely allied are certainly the most generalized group of all reptiles and come nearest in many respects to that order of the Reptilian form from which all others took their origin.
Both in Sphenodon and Crocodilia:
(1) The quadrate is immovable.
(3) The skull is of diapsid type.
(4) Cochlear process is tubular.
(5) Ribs bear uncinate process.
(6) Caudal ribs are fused with vertebrae.
(7) Abdominal ribs are present.
(8) Chevron bones are pre­sent.
(1) The teeth are acrodont in Sphenodon but thecodont in crocodile.
(2) The nasal-opening is double in Sphenodon but single in crocodile.
(3) The vertebrae are amphicoelus in Sphenodon but procoelus in crocodile.
(4) Clavicle is present in Sphenodon but absent in crocodile.
(5) Pecten is absent in Sphenodon but present in crocodile.
(6) Penis is absent in Sphenodon but present in crocodile.
In both Sphenodon and Chelonia:
(1) The quadrate is immovable.
(2) Caudal ribs are fused with vertebra.
(3) Urinary bladder is present.
(4) A process from parietal reaches the squamosal.
(1) In Sphenodon the vomer is paired but in Chelonia it is unpaired.
(2) In Sphenodon sternum is present but it is absent in Chelonia.
(3) Anal opening is trans­verse in Sphenodon but longitudinal in Chelonia.
(4) The penis is absent in Sphenodon but present in Chelonia.
(5) The oviduct in Sphenodon opens dorsally but in Chelonia the opening is ventral.
Some degree of similarities is apparent between Sphenodon on one hand and Crocodilia and Chelonia on the other. But the dissimilarities are more pronounced. Considering these it will not be justified to place the Sphenodon in the same taxonomic rank as that of the orders of Crocodilia and Chelonia.
In both Sphenodon and Lacertilia:
(1) General body plan is identical.
(2) Some Geckos amongst the Lacertilia pos­sess amphicoelous vertebrae.
(4) Caudal vertebrae are separated by septum.
(5) Remnant of notochord is present between the vertebrae.
(7) Chevron bones are present.
(8) Parietal organs are found.
(9) Cloacal glands are present.
(10) Oviducts open dorsally.
(1) In Sphenodon the quadrate is immovable but in Lacertilia it is movable.
(2) The rami are united by ligament in Sphenodon but symphysis is present in Lacertilia.
(3) The vertebrae are emphicoelous in procoelous (except Geckos).
(4) Clavicle and interclavicle are present in Sphenodon but they are absent in limbless Lacertilia.
(5) Conus arteriosus is present in Sphenodon but absent in Lacertilia.
(6) Copulatory organ and pecten are absent in Sphenodon but they exist in Lacertilia.
(7) Uncinate process is present in Sphenodon but absent in Lacertilia.
Huxley (1869) strongly advoca­ted that the Spenodon should be included under Lacertilia as the differences between the two are very insignificant. But Huxley’s view has been opposed by many workers.
(1) In Sphenodon three main arterial trunks come off from a short common trunk probably representing the conus arteriosus of the amphibians. In other reptiles such com­mon trunk is absent.
(2) In Sphenodon both ductus arteriosus and ductus caroticus are pre­sent in moderately developed condition. This feature occurs in Caudata and nowhere else amongst the reptiles.
(3) Distribution of sever­al smaller arteries like carotid, laryngotracheal was also a few vein like abdominal are similar to those of Caudata.
(4) The course of blood through arteria interossea is present in both Sphenodon and Amphibia.
Because of its primitiveness Sphenodon shows affinity with Caudata amongst amphibians. But the reptilian features of Sphenodon are numerous and all that can be said is that Sphenodon is the most primitive amongst the reptiles.
Different views regarding systematic position:
Sphenodon is the sole representative of an order of modern Reptilia, called Rhyncho­cephalia which equals in rank to other living orders.
He stated that the Rhynchocephalia and lizards should be placed in separate groups. He ranked Rhynchocephalia as suborder and grouped in the order Prosauria with another suborder Protosauria.
The Rhynchocephalia is an aberrant group which first appeared in the Triassic, had a mo­dest career through the Mesozoic and is now represented by one conservative living species.
Despite its lizard-like appearance and presence of a well-developed median, parietal third eye in the middle of forehead, Sphenodon is more closely related to crocodiles and alli­gators than to lizards.
Sphenodon is the oldest surviving lepidosaurian reptile which has departed rela­tively little from the diapsid condition in late Permian and still remains in the eosuchian condition.
6. Pough, Janis and Heiser (2002):
The behavioural activity and thermoregu­lation of Sphenodon do not represent the ancestor for lepidosaurs or diapsids.
Discussion and Systematic position:
Sphenodon is a primitive form amongst the living reptiles. Absence of copulatory organs in males, forward extension of the pterygoid to meet the vomer (a feature recog­nisable in stegocephalians), emergence of the three main arterial arches from a short com­mon trunk (probably representing the conus arteriosus of amphibian heart), retention of both ductus caroticus and ductus arteriosus are some of the characteristics which justify the primitiveness of Sphenodon amongst the surviving reptiles.
It cannot be denied that Sphenodon approaches lacertilians more closely than any other groups of reptiles, but because of the retention of many peculiar individual characteristics its place­ment under a separate order Rhyncho­cephalia under the subclass Lepidosauria is thoroughly justified.
Order 3. Squamata [L. squamatus = scaly]:
The order Squamata includes the lizards, snakes and the worm lizards.
The members of this order possess the following characters:
1. The skull bears superior temporal fossa.
2. The maxilla, palatine and pterygoid are immovably articulated with the skull, but the quadrate is movable.
3. Lower jaw is composed of several pieces of bones.
4. The teeth are either acrodont or pleurodont and are borne usually on the maxi­llae, premaxillae and palatines.
5. The vertebrae are of procoelous type.
6. Chevron bones are present.
7. The ribs are single-headed.
8. The cloacal aperture is a transverse slit.
9. One pair of eversible copulatory sacs are present in males.
11. Organ of Jacobson is well-developed.
12. Distribution is cosmopolitan.
The Order squamata have 3 Suborders:
Suborder 1. Lacertilia or Sauria (L. Lacerta, a lizard). About 3000 species:
1. Elongated body is provided with two pairs of limbs except limbless lizards.
2. Usually movable an upper and a lower eyelids are present but in Geckonidae the eyelids are fused. The nictitating mem­brane is also present.
3. Tongue is broad, usually entire.
5. External auditory melatus is present.
6. Sternum with a ‘T’ shaped episternum.
7. Urinary bladder is present.
8. Quadrate is slightly movable.
9. Single temporal fossa present on each side of the skull.
10. Terrestrial, arboreal, burrowing and aqua­tic forms.
It includes the following families:
1. Corytophanidae [Neotropical lizards 9 species]:
The body is laterally flattened and pos­sesses a long tail. Some have crests on head. Arboreal in nature.
2. Crotaphytidae [Collard and leopard lizards 6 species]:
The medium-sized North-American desert lizards. They are about 30 cm long. They have black markings on the neck and shoulder.
3. Hoplocercidae [Terrestrial arboreal lizards of Neotropical region 10 species]:
4. Iguanidae [Iguanas 31 species]:
The length of the body is above 150 cm. Crests, lappets and spines are on the dorsal and caudal regions. Terrestrial and marine herbi­vorous lizards. There are two species of true iguanas—Iguana iguana and I. delicatissima.
They live in the tropical forests of South America. I. Iguana is about 180 cm long and in green and black colour. They are vegetarian in nature. They lay eggs in the holes at the bases of trees. They live in the trees of river banks and can jump into water if they are disturbed.
5. Opluridae [Terrestrial lizards of Madagas­car and Comoro Islands 7 species]:
Oplurus is fairly large and is about 20-30 cm. They are called locally ‘Androngo’ or ‘Sitry’. They can run agilely on rocks and tree trunks and consume small insects.
6. Phyrnosomatidae [North American lizards about 117 species]:
The name of the family comes from the genus Phrynosoma, the horned toad, which possess spikes on head and on the back. The body is flat and has a short tail. They live in the deserts of Mexico and the South-western United States. Other genera are Sceloporus, Urosaurus, etc. The Fence Lizard (Sceloporus undulatus) which is found in the Eastern United States and famous for its speed. It is insecti­vorous and lives in the open pine forests.
7. Polychrotidae [South American lizards about 250 species]:
Most of the species are included under the genus Anolis. Most of the species are tree dwellers and consume flies, spiders etc.
8. Tropiduridae [South American lizards about 200 species]:
9. Chamaeleonidae [Chameleon about 90 species]:
They are recognised by a high body, trian­gular head, a prehensile tail, large movable bulging eyes, a knob-like crest on the nape and a club-shaped protractile tongue. They are mainly found in Africa, Madagascar, India, Southern part of Spain and the West Coast of Mediterranean. They are mainly arboreal but some are terrestrial and insectivorous.
Chamaeleo (= Chamaeleon), Leandria (Armoured chameleon), Brookesia (Leaf chameleon), etc. The Brookesia are much smaller than Chamaeleo and are found in the forests of East Africa and Madagascar. They carry spines on the back. Some are gen­erally blackish in colour and live in dead leaf of the ground (B. nasus). Others are green or grey and live on trees. Chamaeleo zeylanicus is the only Indian species.
10. Leiolepididae [Terrestrial South-east Asian lizard about 14 species]:
Leiolepis, Uromastyx, etc. Uromastyx hardwickii is found in the arid zones of Rajasthan, Punjab and Uttar Pradesh in India.
11. Agamidae [Agamids Asia, Africa, Australia and Southern Europe about 300 species]:
They are recognised by movable eyelids circular pupil, mobile heads and a long tail which is not broken as in other lizards. The skin is covered with overlapping, epidermal keeled scales which may be transformed into spines. The teeth are acrodont and heterodont type. Heterodont type of teeth can be diffe­rentiated into incisors, canines and molars. They are both herbivorous and insectivorous.
Agama (Rock lizard), Calotes (Garden lizard), Sitana (Long tailed lizard), Draco (Flying lizard), Phrynocephalus (Toad-headed agama), Moloch horridus (Thorny devil or spiny lizard of Australia) etc. Moloch horridus (Fig. 8.35A) possesses hygroscopic skin by which they can absorb moisture.
12. Geckonidae [Geckos Warmer parts of the world about 700 species]:
They are medium-sized lizards. The soft skin of the dorsum is covered with granular scales and sparse tubercles. Transverse rows of lamel­lae are beneath the digits which act as adhesive pads for walking on vertical walls. Tongue is protrusible and many males produce sounds. They are insectivorous and nocturnal in habit.
Gecko, (Giant house lizard or Tokay), Hemidactylus (House lizard), Phelsuma (Forest gecko), Ptychozoon (Flying gecko), Phyllodactylus europaeus (European gecko), Uroplatus fimbriatus (Leaf tailed gecko of Madagascar), etc.
13. Pygopodiae [Flap footed lizards of Australasian region about 34 species]:
They are very snake-like and without limbs. Instead of limbs they are represented by flap of skin.
14. Bipedidae [Worm lizards of Mexico 3 species]:
15. Lacertidae [Lacertiols of Old world about 150 species]:
Lacertids have slender body, well- developed limbs, notched tongue and a long pointed tail.
16. Scincidae [Skinks worldwide distribution except Antarctica, about 700 species]:
Body with overlapping, smooth, shiny scales. They have a flat tongue and movable eyelids. Many have reduced limbs. Most of them are insectivorous.
Tiliqua (Blue tongued skinks), Mabuya (Common skink), Riopa (Snakeskink), Ophiomorus (Sand swimmer), Barkudia (Limbless Indian burrowing Skink).
17. Anguidae [Limbless lizards of India, North and South America, Europe, Middle east and Southern China about 90 species]:
Limbless worm-like body. Body is coated by overlapping scales. Its lizard identity is esta­blished by movable eyelids and an ear opening. Fossorial or burrowing types.
European “slow worm” or blind worm (Anguis fragilis). Burmese glass snake (Ophisaurus gracilis) is the only Indian limbless lizard.
18. Varanidae (Monitor lizards of Africa, Southern-east Asia and Australia about 31 species):
They are identified by elongated mobile head, long neck and compressed tail and forked protrusible tongue. Teeth pleurodont.
Varanus komodoensis, V. salvator, V. bengalensis. Lanthanotus is the only earless Bornean monitor.
19. Helodermatidae [Helodermatids of Mexico and South western United States 2 species]:
Heavy bodied lizards. They are brightly coloured with black and red spots.
Heloderma (only poisonous lizard in the world). They are H. horridum, H. suspectum
Suborder 2. Ophidia ( = Serpentes) [Gk. Opidion, diminietive of ophis = a snake L. serpentes, Serpent], About 2750 species:
1. Snakes are typically, scaly, worm-like animals, devoid of limbs, limb-girdles and tympanum (except pythons, boas and blind snakes, where only trace of limb is present). In primitive blind snakes (Fam. Typhlopidae) vestiges of pelvic bones are present.
2. They have no movable eyelids, and eyes are by protected by a scale modified as transparent spectacles.
3. Quadrate is highly flexible. Maxillae, palatines and pterygoids are also freely movable. The rami of the mandible are connected by elastic ligaments. So they can swallow prey several times larger than their body’s diameter. The absence of pec­toral girdle can correlate of swallowing animals larger than the body size.
4. Sternum and episternum are absent.
5. They have a deeply forked tongue which is highly sensitive to temperature and used as an organ of touch and smell. They can protrude the tongue through the notch of the upper snout even when the mouth is closed. The organ is used to follow the prey trails at night and for sex recognising.
6. Temporal fossae are totally absent due to secondary mode of adaptation.
7. Vomeronasal or Organ of Jacobson is well-developed. Particles that adhere to the tongue, can be withdrawn into the mouth and the tip of the tongue with par­ticles is projected into the cavity of vomeronasal organ where the odour of the particles can be detected. Though this organ is present in other groups of verte­brates, specially in lizards but functionally it is highly developed in snakes.
8. Tympanic membrane, cavities and eustachian tubes are reduced or absent. In burrowing forms these are reduced. Columella auris (= stapes) articulates with the quadrate.
So it is believed that the snakes cannot pick up the air-borne vibrations but it is assumed that they can perceive the earth-borne vibrations through their sensitive bodies or as Young (1981) pointed out that snakes can hear the air-borne vibrations only of low frequency at 300 Hz, transmitted through the bones of the jaw.
9. Scleral ossicles or cartilages are absent in the eyes of snakes.
10. Snakes are progressed through the lateral undulations of the body. The zigzag movement is highly affected by the addi­tional intervertebral articulations known as Zygantra and Zygosphenes. Vipers and some boas can move by muscular move­ments of the ventral scales. The slipping during the movement is prevented by the enlarged transverse ventral scales.
11. Transpalatine or ectopterygoid (the bone connecting maxilla and pterygoid) is pre­sent.
Male and female snakes copulate like other vertebrates. Major snakes are oviparous, some are viviparous (e.g., viper and sea snakes). Oviparous female lays between 6 and 20 or more eggs.
Viviparous female snakes give birth to between 6 and 20 young ones. Parental care phenomenon is negligible. A very few snakes (e.g., Cobra, King cobra, Kraits, Pythons) remain near their eggs and guard them against intruders. A female king cobra (Ophiophagus hannah) can make nest of leaves.
All snakes are carnivorous and eat live prey. The larger snakes capture rats while smaller ones feed on mice, smaller birds, lizards even frogs. Snakes eat insects. Certain snakes have been adapted in feeding snails and slugs. One snake of Africa (Dasypeltis scabes) and other in India (Elachiston wester-manni) are egg eaters.
Some snakes like the Krait (Bungarus sp.) and the king cobra (Ophiophagus hannah) feed exclusively on other snakes. Pythons capture larger mammals and swallow small pigs and deer whole.
Generally the life span of snakes ranges from 10 to 20 years. In some cases they can live as long as 30 years. The life span is known only from the zoo record or personal captivity.
About 2750 species of snakes are found in warmer regions of the world. Nearly 244 species of snakes have been recorded from India of which only 52 are poisonous. Out of 2750 known types of snakes, less than 200 are dangerous to human beings.
The Suborder Ophidia include the follow­ing families:
1. Family Boidae [Non-poisonous Boas and Pythons]:
Stout body short tail vestigial hind limbs in front of the vent. Arboreal and amphibious in habit.
Indian Rock Python (Python molurus), Red Sand Boa (Eryx johni), Boa (Boa con­strictor).
Worldwide except New Zealand.
2. Family llysiidae (Anilidae) [Non-poiso­nous ilysia (Anilius)]:
Head small, tail short and blunt scales small, smooth and irridescent hind limbs appear as spines at the sides of the vent.
Anililus (Southern America and South East Asia).
3. Family Typhlopidae [Non-poisonous Boas or worm snakes]:
Small worm-like blunt head and tail, over­lapping smooth shiny scales teeth on only maxillary bones some burrowers.
Common Indian worm snake (Typhlina bramina) Beaked Indian blind snake (Typhlops acutus).
Tropical and subtropical in both hemispheres.
4. Family Leptotyphlopidae [Non-poiso­nous allied to family Typhlopidae]:
Teeth only on lower jaw vestiges of pelvic bones present burrowers. Example: Leptotyphlops blanfordi.
S. E. Asia, Africa, North and South America and West Indies.
5. Family Uropeltidae [Non-poisonous Shield Tails or Rough Tails]
Stout body, short tail, ending obtusely, and covered with scales. Burrowing forms. No ves­tiges of limbs.
Ocellate Uropeltid (Uropeltis ocellatus) Travancore Shield-tail (Rhinophis travancorius).
Southern part of India and Sri Lanka.
6. Family Xenopeltidae [Non-poisonous Sunbeam Snake]:
Body cylindrical long tail overlapping irridesent abdominal scales burrowers. Sole representative in South-east Asia.
7. Family Colubridae [Most of the living snakes]:
It is divided into two groups:
(i) Aglypha – including the non-poisonous forms and
(ii) Ophisthoglypha – including the poisonous forms].
Medium-sized snakes, tail cylindrical and pointed. Opisthoglyphs are moderately poi­sonous and possess one or more pairs of grooved fangs at the rear end of the maxilla.
Aglypha – All teeth solid. Rat snake (Ptyas mucosus). During breeding season, the sexual dimorphism is seen in the rat snake (Ptyas mucosus). Males are longer than females and spiny structures are also present around the hemipanis. Opisthoglypha – Common wolf sake (Lycodon aulicus) Flying snake (Chrysopelea ornata) African Boomslang (Dispholidus).
Worldwide except New Zealand.
8. Family Dasypeltidae [Non-poisonous Egg-eating snakes]:
Olive colouration, black and yellow spots on its back. The eggs can crush with tooth-like processes of the neck vertebrae.
Indian egg eater snake (Elachistodon westermanni), African Egg-Eater (Dasypeltis).
North Bengal and Bihar, Africa.
9. Family Elapidae [Highly venomous Cobras, Kraits, Mambas, Australian Black and Tiger snakes, Death-Adder, Coral Snakes etc.]:
Tail cylindrical and tapered tubular fangs at the front of the maxilla.
Cobra (Naja) Kraits (Bungarus) African Black Mamba (Dendroaspis angustipis) Australian Tiger Snake (Notechis scutatus) Australian Death Adder (Acanthophis antarcticus), etc.
The most venomous land snake is ‘Tiger Snake’ (Notechis scutatus) found in Kangaroo. Island (South Australia), whose average venome yield is sufficient to kill 300 sheep.
Most of the part of the world except northern Eurasia and northern part of U.S.A.
10. Family Hydrophidae [Venomous Sea snakes]:
Tail compressed and rudder-like except homalaspines, natricines and acrochordials whose tails are similar to those of land snakes.
Sea snake (Hydrophis caerulescens) Hook nosed sea snake (Enhydrina schistosa).
11. Family Viperidae [Venomous vipers, Pit vipers, Rattle snakes etc.]:
Triangular head small scales on head tail cylindrical canalized fangs in front of the maxillary bone.
Puff-Adder (Bitis arietans of Africa Horned viper (Cerastes cornutus, North Eastern Africa).
Russell’s viper (Vipera russelli, India, Sri Lanka, Myanmar and Thailand) Fer-de-Lance (Bothrops lanceolatus, South America) Common Rattle Snake (Crotalus horridus, U.S.A.) and Saw-scaled viper (Echis carinatus, India).
Major portion of the world except Madagascar and Australia.
Suborder 3. Amphisbaenia [Gk. amphi, both + baino, to go] About 140 species:
(i) Most of the species of the worm lizards are limbless (except chirotes).
(ii) Worm-like body with soft skin possessing numerous rings which are divided into little squares.
(iii) The eyes and ears are completely con­cealed beneath the skin.
(iv) The tail is very short.
(v) The skull is compact and highly ossified which helps them to lead the fossorial life.
(vi) Teeth either acrodont or pleurodont.
(vii) They crawl easily both forward and back­ward with slightly vertical waves – hence the name ‘both ways’.
(viii) Food includes earthworms, insects and spiders.
Worm lizards are confined to mainly South America, Mexico, West India, South Western United States, Africa and Southern Europe.
Amphisbaena fuliginosa (South America and West Indies), Blanus (Mediterra­nean region).
Subclass 5. Archosauria [Ruling reptiles]:
(i) Skull was of diapsid type and lacked inter-parietal and parietal foramina.
(ii) Palatal teeth were lost in some forms. Some forms were toothless.
(iii) The lower jaw was with vacuities between dentary and angular.
(iv) In some forms bipedality (two footed locomotion) was more marked and the girdles were modified accordingly.
Order 1. Thecodontia (Tri.) [Socketed teeth]:
They were present during Triassic period. Members belonging to the suborder Pseudosuchia under this order were small in size.
(i) They were carnivorous in nature.
(ii) The teeth were sharp and were lodged in sockets along the jaw edges.
(iii) The hind legs were long and indicated the dawn of bipedality. The members of the other suborder Phytosauria were aquatic.
(iv) The skull was elongated.
(v) Array of holding and stabbing teeth were present on the jaws.
(vi) The external nares were situated high above the skull level.
It is considered that all later archosaurs have evolved from thecodonts e.g., dinosaurs, birds and others (Romer and Parsons, 1986 Kardong 2002).
Euparkeria, Orninthosuchus, Phystosaurus.
Order 2. Crocodilia or Loricata (Tri.—Rec.) [L. crocodilus = a crocodile L. loricatus = clad in mail.] 21 species:
The corocodilian evolution is believed to date back to a periH over 200 million years, i.e., between Permian and Triassic. The oldest crocodilian fossil is Proterochampsa barrionuevoi which has been discovered from Triassic beds of Western Argentina. Another fossil of uppermost Triassic, Protosuchus, has discovered from Arizona. These two fossils with others formed a group, called Protosuchia. The protosuchians were about 1.5 m in length.
The mesosuchians were evolved from the protosuchian ancestors and were represented by Teleosaurus and Steneosaurus. They lived in huge numbers from lower Jurassic to the end of Cretaceous. The nasal passage of the mesosuchians was completely separated from the mouth cavity.
During Cretaceous period, the advanced crocodilians, the Sebacosuchians and the Eusuchians, arose from the Mesosuchians. The sebacosuchians line of evolution was repre­sented by Sabacus and Baurusuchus. These animals were restricted to South America and soon became extinct. The eusuchian line of evolution represents three modern groups of Crocodiles — Crocodylidae, Alligatoridae and Gavialidae.
Among the major groups of reptiles, the Order Crocodilia includes the largest forms of living reptiles.
1. They are carnivorous and freshwater rep­tiles. They swim by the undulation of their powerful tail.
2. The limbs are not powerful as the tail and are used in carrying the body on land.
3. The forelimbs are shorter than the hind and have five digits in the forelimbs and four digits in the hind limbs. The digits of the forelimbs are webbed.
4. The body is elongated and the skin bears epidermal scales which are supported by dermal bones or scutes. The scales are supported by dermal plates osteoderms.
5. The tail is laterally compressed.
6. The cloacal aperture is longitudinal, i.e., elongated in the direction of the long axis of the body.
7. Males are provided with a single and median erectile copulatory organ.
8. A clitoris occurs in female.
9. The teeth are thecodont (advanced feature) and are borne on premaxillae, maxillae and dentaries.
10. The teeth contain persistent pulp.
11. The oesophagus can be distended to store food.
12. The stomach suggests a bird’s gizzard for the muscular walls are strong, and glan­dular pyloric end is twisted upward. Very often stones measuring about 2.5 cm in diameter are found inside stomach. The cavity of the mouth is bounded behind by two soft transverse membranes which meet when the animal draws the prey.
13. The nostrils are situated at the tip of the snout.
14. The external narial openings are opened by longitudinal dilator muscle and closed by a constrictor muscle. During submer­sion in water the external narial openings are closed. The muscle fibres comprising both these muscles are un-striated and are controlled by the sympathetic nervous system.
15. The internal nasal aperture is situated at the back of the mouth.
16. The lungs are invested by pleural sacs.
17. An incipient diaphragm (advanced fea­ture) is situated between thoracic and abdominal wall.
18. The heart (Fig. 8.59C) is four-chambered and the inter-ventricular septum is com­plete (advanced feature).
19. The roots of the left and right aortic arches are twisted and communicated by the foramen of Panizza (Fig. 8.59) through which an interchange of blood does not take place.
20. The crocodilians are ectothermic animals.
21. The brain is well-formed. The cerebellum shows the development of a median lobe (vermis) and two lateral lobes (flocculi).
22. The eyes are provided with pecten (advanced feature).
23. The nervous system and the sense organs show many avian features.
24. The auditory organs have a substantial lagena.
25. The tympanic membrane is sunk in a pit (advanced feature) and protected by two scaly movable flaps. These flaps are ope­rated by special muscle and shut the exter­nal auditory meatus when the crocodiles dive.
26. The eggs are laid in excavated burrows and need no incubation.
27. The skin glands are situated on the margin of lower jaw, round cloacal aperture and on dorsal scutes. Secretion of the glands smells like musk and becomes very strong during breeding season.
28. The skull is highly sculptured with persis­tent sutures (Fig. 8.60).
29. Inter-orbital septum with large alisphenoid is present.
30. Inter-orbital septum is well-developed.
31. Maxillae, palatine and pterygoids meet at the middle line of the roof of the skull and determine the position of posterior nares.
32. Transpaiatine bone is present.
33. The quadrate is large and immovable.
34. The inter-parietal foramen is absent.
35. Internal nasal aperture is single.
36. A bony secondary palate is present which is formed by the fusion of shelves grown out from the maxillae, palatines and ptery­goids (advanced feature).
37. Lower jaw is composed of a cartilaginous articular working on quadrate and five membrane bones.
38. The vertebral column is divisible into cer­vical, thoracic, lumbar, sacral and caudal regions.
39. Vertebrae are either amphicoelous or pro­coelous excepting the first two cervicals, sacrals and first caudal.
40. There is a pro-atlas in between skull and atlas.
41. The first caudal has convexity at both ends.
42. There are two sacral vertebrae.
43. The caudal vertebrae are provided with chevron bones.
44. The anterior thoracic vertebrae bear bifid and elongated transverse processes.
45. Sternal and abdominal ribs (gastralia) are present.
46. Sternal ribs have uncinate process. Most of the ribs are double-headed (advanced feature).
47. The pectoral girdle consists of dorsal scapulae and ventral coracoids.
48. The clavicles are absent.
49. The epicoracoids are thin strips between sternum and coracoid.
50. The episternum is feebly developed.
51. The coracoids are perforated.
52. The pelvic girdle consists of large ilia, pubes and ischia.
53. The epipubis is present and the symphysis is ischio-pubic in nature.
54. The pubes are small and do not participate in the formation of the acetabulum.
The common term “crocodile” comes from the Greek Krokodeilos meaning lizard. Crocodilians may have descended from some group of Triassic thecodonts, the stem group of all archosaurian reptiles and birds.
Crocodilians are amphibious vertebrates, spending mainly in water and a part on dry land. They live in rivers, lakes, ponds, artificial water tanks, marsh lands, swamps, brackish-waters and estuaries. On’ land they inhabit forests, wooded grasslands, grasslands, deserts and savannas.
They are the mainly inhabitants of tropics (except the American Alligator, Alligator mississippiensis, Chinese Alligator, A. sinensis and other five species of crocodilians), although a few live to the subtropical regions of the world.
The living crocodilians represent 7 genera and 21 species.
In reptiles, sex deter­mination is concerned with either genetic or environmental. Temperature-dependent sex- determination (TSD), a type of environmental sex determination, is related to many reptiles including turtles, lizards and crocodiles. All crocodilians incubate their eggs at tempe­ratures near about 30°C (86°F).
The embryos die if they are exposed to below 27°C (81 °F) and above 34°C (93°F) temperatures. In case of American Alligators and Caimans, high tem­peratures of 32°-34°C (90°-93°F) yield male, low temperatures of 28°-30°C (82°-86°F) pro­duce females. In Australian crocodile, females are produced both at high, 30°-34°C (86°-93°F) and low temperatures, 25°C, and males are produced at intermediate tempera­tures (31° – 33°C).
The mode of courtship before copulation is complex and most advanced type among reptiles. Both courtship and copulation take place in water. Sexual dimorphism in size occurs in most of crocodi­lians, in which males grow faster and attain maturity than females.
Male Indian Mugger (Crocodylus palustris) becomes mature in about 10 years old. Before courtship the jaw slap or head slap of the males attracts the female, and the female responds with her own jaw slap. In the month of January or February, the female initiates courtship by swimming around a male with head upraised.
The male also responds by snout rubbing cir­cling and submerging. Within 40 days after copulation the female chooses a bank site and digs a “L shaped hole” at night. She lays about 25-30 eggs in the hole but sometimes 46 eggs are known. After egg laying, the mother mug­ger guards the nest from any intruder for about two months.
Female Salt water crocodiles (C. porosus) of Indo-Pacific region lay eggs on mound nest. Clutches of eggs include 60-80. Females make nest only in winter season and parental care has been observed. Mound nest for egg laying is found in most of the crocodiles. Snout rubbing, mounting by both partners, circling are the signals of courtship in Gharials (Gavialis gangeticus).
Courtship starts in December and mating takes place in January and February. The females first indicate the willingness of mating by raising the snout upward. The females make nest on a high, steep sandy bank of rivers. The nest is 50 cm deep hole. The female deposits about 35-100 eggs in the hole at night.
Caimans and Alligators make mound nests by fresh vegetation soil and leaf litter. Visual signals and vocal communication use during courtship. Normally at the time of courtship the males lift their heads high and hold their tails vertically out of the water. Females American Alligator (Alligator mississippiensis) lay about 45 eggs. Para-natal care has been noticed.
Diet: By the structure of jaws and teeth, it appears that crocodilians are efficient preda­tors but most of the crocodiles are nocturnal hunters and spend at most of the day time by basking. So field observations during day do not reveal a large number of prey species. The variety of prey species is counted by the exa­mination of stomach contents.
The prey species is markedly different with the change of age, size and habitat. Diet of young crocodilians includes insects, small fishes, snails, crabs, shrimps, tadpoles and frogs. Food of sub adult and adult crocodilians consists of a bulk of fish (about 70%), crabs, terrapins and turtles, birds and small and large mammals.
With the change of the habitat, their food also changes. In the brackish-water and in the estuarine zone, the diet of the crocodilians includes mud or fiddler crabs, mud skippers, prawns, shrimps, insects, molluscs and a variety of fishes. Crocodilians of the swampy and freshwater system feed on tadpoles, frogs, snails and a variety of freshwater fishes.
The food of long snouted crocodilians such as Gharial (Gavialis gangeticus), False Gharial (Tomistoma schegeli), African Long Snouted Crocodile (Crocodylus cataphractus) etc. is mainly fish. Crabs, frogs, birds and small mammals are also reported. The Estuarine crocodile (C. porosus) of Indo-Pacific region subsists on cattle, buffaloes, crab-eating mon­keys, squirrels, goats, sheep wallabies and some birds.
Fish also forms a part of the diet. Diet of adult Mugger (C. palustris) includes frogs, snakes, fish, birds and small mammals. Among mammals, monkeys, sambars (Cervus unicolor) and gaur (Bos gaurus) are recorded. Large adult Nile Crocodile (C. niloticus) eats antelope, zebra, warthog, man and large domestic animals. Adult American Alligator
(Alligator mississippiensis) consumes turtles, snakes, fish, birds and small mammals. Very occasionally eating of man has been reported.
The Order Crocodilia is exemplified by crocodiles, alligators and ghariais. These three varieties are characterised by having individual characters which are shown in Table 35.
Order Crocodilia include 3 families, namely:
(i) Crocodylidae (e.g., crocodiles),
(ii) Alligatoridae (alligators and Caimans) and
Family 1. Crocodylidae:
The crocodiles include three genera: Crocodylus, Osteolaemus and Osteoblepharon. The genus Crocodylus is found in Africa to South China, Australia, New Guinea, Western Pacific and Southern United States to Venezuela. This genus is characterised by having nasal bones dividing the nasal aper­ture into two.
The genus, Osteolaemus, is found in Western Africa and is characterised by having undivided nasal aperture and the snout turned up in front. The genus, Osteoblepharon, is found in Congo having close similarities with Osteolaemus but the snout is not turned up.
Family 2. Alligatoridae:
The alligators are placed in two genera: Alligator and Caiman. The genus Alligator is widespread in southern parts of the United States and Southern China. The nasal bones divide the nasal aperture in this -genus. The other genus, Caiman, is found in tropical South America. The nasal aperture is undivided in this genus. The biggest alligator — Alligator mississippiensis is about 6 metres or 20 feet in length, but harmless.
Family 3. Gavialidae:
The ghariais are included under two genera: Gavialis and Tomistoma. The genus Gavialis is found in northern part of India and is characterised by having 27-29 teeth on each side of the upper jaw. The genus Tomistoma is abundant in Borneo and Sumatra, and differs from Gavialis by having 20-21 teeth on each side of the upper jaw.
The Indian gharial, Gavialis gangeticus has been recorded to exceed about 6 m in length. There is no accurate record as to the longe­vity of different forms. An American alligator has been recorded to have lived to the age of about 56 years.
Order 3. Saurischia (Tri.—Cre.) [Gk. Sauros = lizard ischion = hip or pelvis]:
(i) The members of this order were cha­racterised by having triradiate pelvic girdle.
(ii) Teeth were borne by the premaxillae.
Tyrannosaurus, Yaleosaurus, Gorgosaurus.
Order 4. Ornithischia (Tri.—Cre.) [Gk. Ornithos = bird ischion = pelvis]:
(i) The order Ornithischia included the ‘bird-like’ dinosaurs.
(ii) The members of this order possessed a ‘predentary’ bone in the mandible which supports the beak.
(iii) They were all herbivorous.
Iguanodon, Trachodon, Stegosaurus, Nodosaurus.
Order 5. Pterosauria (Pterodactyla) (Tri.— Cre.) [Gk. Pteron = wing sauros = lizard]:
(i) This order includes the fossil flying reptiles.
(ii) The bones were pneumatic like that of birds.
(iii) The forelimbs became converted into wings.
(iv) The fourth finger was greatly enlarged (‘wing finger’) to support the membra­nous wing.
(v) The fifth finger was lacking and the other fingers were small.
(vi) The sternum was keeled.
Pteranodon, Pterodactyl us, Rhamphorhynchus (Fig. 8.62).
Subclass 6. Synapsida (Carb.—Per.):
i) They are considered as mammal-like reptiles.
ii) The skull was provided with a single and lateral temporal vacuity lying below the post-orbital and squamosal.
iii) The supraoccipital was broad.
iv) The lower jaw was flat and the teeth were of heterodont type.
v) The shoulder girdles were with coracoids and pre-coracoids.
vi) The orders under the subclass are:
Order 1. Pelycosauria (Carb.—Per.) [Gk. Pelykos = an axe sauros = lizard]:
i) They existed between upper Carboni­ferous and lower Permian.
ii) The skull was with temporal vacuity.
iii) In some forms, like Dimetrodon, the neural spines were much elongated and formed a specialized structure, called a “sail” along the back that consist of an extensive flap of skin supported internally a row of elongated neural spines.
iv) Some forms were carnivorous but majo­rity were vegetarian.
Dimetrodon (Fig. 8.63), Edaphosaurus.
Order 2. Therapsida (Per.—Jur.) [Gk. Therion = mammal apsida = loop]:
i) They existed between middle Permian and lower Triassic.
ii) They constituted a very important group from the stand-point of evo­lution. According to Romer, they bridged the entire evolutionary gap between a primitive reptile and a mammal.
iii) In advanced therapsid reptiles the occipital condyle was double.
iv) The temporal opening in the skull was big.
v) The quadrate and quadratojugal were greatly reduced.
vi) In some forms, a secondary palate was present.
vii) The teeth were distinctly differentiated into the incisors, canines and molars.
viii) The group is regarded as the’ precursors to mammals.
Cynognathus (Fig. 8.64) Lycosaurus, Lystrosaurus (Fig. 8.65).
Phylogenetic history of Reptiles:
The reptiles underwent extensive adaptive radiation and exploited not only the diverse terrestrial modes of life, but also invaded water and the air. As a group the reptiles reigned on earth for about 125-150 million years. After their dominance they were eventually replaced by birds and mammals.
Just at the onset of Mesozoic era, five major reptilian groups were present. All these groups have evolved from the Cotylosaurian stem reptiles of Permian period. One of the groups, the thecodonts hold the ancestry of birds, crocodiles, lizards and snakes, pterosaurs and dinosaurs (comprising of ornithischia and saurischia).
A second repti­lian stock evolved into the modern turtles. The third and fourth groups gave origin to Ichthyosaurs and Plesiosaurs. The fifth reptil­ian stock, the therapsids, was the mammal like reptiles.
These mammal-like reptiles gave origin to the mammals. Fig. 8.66 relates the probable phylogenetic tree of different reptiles. The different reptilian varieties did not all flourish at the same time in the Mesozoic era. The Triassic period was domi­nated largely by the thecodonts and therap­sids.
True mammals were evolved in late Triassic period. The birds arose during Jurassic period when Ichthyosaurs were also abundant in the sea. The evolutionary trans­formation of one of the thecodont groups into birds is well-documented by the fossil bird, the Archaeopteryx. The flying reptiles, the Pterosaurs flourished in Cretaceous period when the dinosaurs as well as the plesiosaurs dominated the earth.
At the end of the Cretaceous period, virtually almost all the reptilian multitude became extinct. They are now represented by the lizards, snakes, tur­tles, crocodiles and Sphenodon. The causative agent of such large-scale extinct of reptiles is not fully explored. Climatic changes at the close of Mesozoic era have possibly played the decisive role as the rep­tiles as a group are exothermous animals.
As a result of the Laramide revolution towards the close of Cretaceous period the climates became colder. The advent of colder climates caused the destruction of tropical and subtro­pical vegetation thus disrupting the food chain. The destruction of the Mesozoic rep­tiles paved the way for the evolutionary expansion of the birds and mammals.
Research work on Indian herpetology:
The research work on Indian reptiles started to publish from the 19th century. Gray (1825-1875) published the works on turtles. Gunther’s “The Reptiles of British India” in 1864, “Blyth’s descriptive catalogue of the Reptiles of British India” in 1870 are considered valuable books to the herpetologists.
Anderson (1871-1872), Murray (1884-1887) and Stoliczka (1870-1873) published the works on lizards. Beddome (1863-1886) published the works on uropeltid snakes of South India and lizards of Western Chats.
Boulenger’s classic work “Fauna of British India — Reptilia and Batrachia” in 1890 set the course of modern ophiology. Annandale (1912-1915) produced a detailed work on fresh­water turtles. M. A. Smith’s (1933, 1935, 1943) volumes — The Fauna of British India including Ceylon and Burma consider the standard work on the subject.
Indian herpetologists like Mahendra (1953) on snakes, Ganapati and Rajyalakshmi (1953) on limbless skink (Barkudia insularis), Gharpurey (1962), Deoras (1965), Biswas and Acharjyo (1977, 1976), Daniel (1983), Das (1985) and Murthy (1986) have contributed much on rep­tiles.
5375 extant species have recorded from the surface of the world under 38 families of which Indian reptiles represent 462 species, which are included under 23 families. The first authentic faunal book on Indian reptiles is Boulenger’s Fauna of British India, Reptilia and Batrachia, pub­lished in 1890. The number in the list of species has increased more at present since the publi­cation of Boulenger’s Reptilia and Batrachia.
Order Chelonia is represented by 32 species which are included under five families. All the five species of sea turtles mentioned previously included under the families cheloniidae and Dermochelidae.
Family Emydidae (freshwater terrapins) contain 7 genera and 17 species. The genera are Batagur, Cyclemys, Heosemys, Geoclemys, Hardella, Kachuga and Melanochelys. Batagur includes a single species, Batagur baska which is found in the rivers and estuaries of Sundarbans (W. Bengal).
It is recognised by its large size and four claws in the forelimb instead of 5. Cyclemys is identified by hexagonal neural plates short sided behind and plastron united to the carapace by the ligamentous tissue. It contains 2 species.
Cyclemys dentata and C. mouhati, both occur in Assam. Heosemys includes a single species — H. silvatica. H. silvatica, a Kerala forest terrapin, is known from the dense forests of Cochin in Kerala. It is recognised by tricarinated, black coloured carapace and two-spotted, yellow coloured plas­tron.
It is a rare species. After the first record in 1911, rediscovery was done in 1982. Geoclemys also includes a single species, G. hamiltoni. C. hamiltoni, the spotted black terrapin, occurs in the Ganges and Indus river systems of Northern India. It is a rare species and recognised by black coloured carapace with yellow spots and radiating streaks.
Hardella includes a single species – Hardella thurgii. H thurgii, Brahminy terrapin, is found in the Ganges, the Brahmaputra and the Indus river systems. Its carapace somewhat flattened and dark brown or dark grey in colour. Plastron is yellow in colour with a large black patch. Digits are fully webbed.
Kachuga is identified by broad alveolar sur­faces of jaws with a median ridge. The forelimbs possess 5 claws. It contains 6 species. Kachuga smithi, Smith’s terrapin, is found in the lower parts of the Ganges in W. Bengal.
Carapace olive brown to pale brown and plastron black. K. tentoria, Deccan saw back terrapin, occurs in the Mahanadi, the Godavari and the Krishna river sys­tems. it is known by paler carapace, olive head and a red spot behind tympanum. K. tecta, Roofed terrapin, occurs in the Ganges, the Brahmaputra and the Indus river systems.
It is a small sized and has olive green coloured carapace with small back spots. K. dhongoka,’Dhongoka terrapin, is found in North India, specially in the eastward of Corbett National park.
It is a medium sized terrapin, with a rough texture and olive coloured carapace, and a black stripe runs along the mid back. K. kachuga, Sail terrapin, is found in the Gangetic system of U.P., Bihar and W. Bengal. It is the largest sized terrapin, known by brown or olive coloured carapace and yellow coloured plastron. The neck possesses seven reddish-brown lines.
K. sylhetensis, khasi hills terrapin, is known from the hill areas of Nagaland and Meghalaya. The species is identified by olive brown carapace and yellow coloured plastron. Head and legs are brown and longitudinal streaks on the neck region.
Melanochelys includes two species, M. trijuga and M. tricarinata. Melanochelys trijuga, Indian pond terrapin, has been recorded from W. Bengal, Bihar, Tamil Nadu, Kerala, Karnataka and Maharastra. It is the most common terrapin and is a resident of slow flowing or stagnant waters.
It is identified by dark brown or blackish carapace, yellow bordered plastron, flattened limbs, fully webbed digits and inwardly curved shell margin.
Family Trionychidae (freshwater or mud turtles) include three genera and six species. Lissemys punctata punctata, North Indian flap- shell turtle, is known by its oval-shaped carapace, short tail, and fully webbed digits. Yellow spots are on the carapace and head.
It is found in the Indo-Gangetic plain region. L. P. granosa is found in the south of the Ganges. It is distinguished from the above species by the absence of yellow spots. It is a resident of ponds, reservoirs and river systems.
Chitra indica, narrow necked soft shell turtle, is found in the Ganges and Indian river systems. It has long, narrow head and dorsolateral eyes, close to the proboscis. Black coloured head with light coloured streaks.
Trionyx gangeticus, the Ganges soft shell tur­tle, is found in the Ganges, and the Mahanadi river systems. It is dull olive or green above and gree­nish black streaked head. Youngs have intricate black reticulation and four distinct ocelli on the carapace.
Trionyx leithi, Deccan soft shell turtle, is found in the river of peninsular India. The cara­pace is olive green with lighter vermiculation’s. Longitudinal black coloured streaks run from nape to eyes.
Trionyx hurum, Peacock soft shell turtle, is found in the lower reaches of the Ganges and the Brahmaputra. It is identified by olive green coloured carapace and with black reticulations. Head is marbled with back lines and yellow spots. Well-marked ocelli are found on the carapace at young.
Emydidae (land tortoises) is known by four or five digits and pillar-like limbs. It includes two genera and four species. Geochelone elegans, Starred tortoise, is found in A. P., Tamil Nadu, and Karnataka and also in the hilly tracts of Udaipur, Rajasthan. It is identified by dome-shaped carapace with humps. Each hump has a radiating yellow streaks. Fore-limbs are flat­tened and hind limbs cylindrical.
Geochelone elongate, East Asian tortoise, is found in the hilly areas of east India. C. travancorica, Travancore tortoise, occurs in Kerala and Karnataka. G. elongata is identified by yellow coloured cavapace with black blotches.
Lizards are represented by 153 species and are included under 8 families. The families are Gekkonidae (Geckos), Agamidae (Agamids), Chamaeleonidae (Chameleons), Scincidae (Skinks), Lacertidae (Lacertids), Anguidae (Burmese glass snakes), Varanidae (Monitors) and Diabemidae.
Geckonidae include Eublepharis, Stenodactylus, Cyrtodactylus, Cnemaspis, Calodactylodes, Davidogecko, Hemidactylus, Cosymbotus, Cehyra, Hemiphyllodactylus, Gecko, Ptychozoon, Phelsuma, Teratolepis and Laphopholis. Geckonidae include 55 species of which House Gecko (Hemidactylus flaviviridis), Brook’s Gecko (Hemidactylus brooki), Rock Gecko (Hemidactylus maculatus), Tokay (Gecko gecko), Fat Tailed Gecko (Eublepharis macularius), Banded Rock Gecko (Cyrtodactylus dekkanensis), Gliding Gecko (Ptychozoon kuhli), Golden Gecko (Calodactylodes aureus) are well-known.
Agamidae is represented by 13 genera and 38 species. Common Garden hizard (Calotes versi­color, Fan Throated Lizard (Sitana ponticeriana), Flying lizard (Draco dussumieri), Spiny Tailed Lizard (Uromastix hardwickii) are well-known.
Chamaeleonidae is represented by a single specles-Chamaeleon zeylanicus which ranges throughout Southern India and extends up to eastern part of Orissa. It is known from Digha (W. Bengal) and Chandaneswar (Orissa) border. The local people of Orissa call them “Bahurupee Endua”.
Scincidae include more than 39 species under 12 genera.
The genera are:
(i) Mabuya (12 species, throughout India)
(iii) Sphenomorphus (2 species, throughout India)
(iv) Scincella (8 species, mountainous regions of the Himalaya and the Western Ghats, South India)
(v) Ablepharus (1 species, North West India)
(vi) Riopa (5 species, throughout India)
(vii) Ristella (4 species, Western Ghats, South India)
(viii) Eumeces (2 species, Kashmir)
(ix) Ophiomorus (1 species, Punjab and Gujarat)
Barkudia insularis, only Indian limbless bur­rowing skink, found in Barkuda Island of Chilka lake, Orissa and Waltair Coast of A.P. It is identi­fied by its elongated body and a dozen lines that run longitudinally on the back and sides,
(xii) Sepsophis (Single species).
Among skinks, Mabuya is more or less com­mon throughout India. Mabuya carinata, Common or Brahminy skink, is most common throughout Bengal. It is a more or less common denizen around our houses. It is identified by shiny, brown, olive or bronze above with longitudinal light band from behind the eye to the base of tail. Under sur­face is white or yellow. Darker spots often present on the dorsum. In Bengali it is called “Anjani”.
Lacertidae contain, 5 genera which include 9 species. The family is poorly represented in India. Takydromus (1 species) Acanthodactylus (1 species) Cabrita (2 species) Ophisops (3 species) Eremias (2 species). Among the above mentioned genera, Cabrita is found in the forests of South India and Ophisops is found both in North and South India.
Anguidae is represented by a single species — Ophisaurus gracilis (Burmese glass snake). It has been recorded from Darjeeling and Khasi Hills (Eastern India). It has also recorded from Simla in Western Himalayas.
Varanidae is represented by 4 species. They are (i) Varanus bengalensis, common Indian Monitor (throughout India) (ii) Varanus flavescens, Yellow Monitor (Gangetic Plain from Punjab to Bengal) (iii) Varanus salvator, water Monitor (Bengal, Bengal) and Varanus griseus, Desert Monitor (North West India).
Dibamidae is represented by 3 species under the sole genus Dibamus. The only Indian worm lizard, D. novaeguinae, found in the Nicobar Islands and is a degenerate type of skink.
Indian serpents or snakes are represented by 235 species of which 50 are poisonous.
These species are included under 9 families, namely:
(i) Typhlopidae, Blind or work Snakes (14 species, throughout India),
(ii) Uropeltidae, Shield tails or Rough tails (33 species, South West India)
(iii) Boidae, Boas and Pythons (4 species, all over India)
(iv) Xenopeltidae, Sunbeam snakes (1 species, Andamans)
(v) Colubridae, Colubrids (130 species, throughout India)
(vi) Dasypeltidae, Egg eating snake (1 species, Northern Bengal and Bihar)
(vii) Elapidae Coral snakes, Cobras, Kraits (15 species, throughout India)
(viii) Hydrophidae, Sea snakes (20 species) and
(ix) Viperidae, Viper and Pit vipers (20 species).
Order Crocodilia include Crocodiles, ghadals, Caimans and alligators. Three Indian species belong to the order Crocodilia, namely, the estuarine crocodile, Crocodylus porosus, the Mugger or Marsh Crocodile, Crocodylus palustris and the Gharial, Gavialis gangeticus.
Estuarine or Salt water Crocodile, C. porosus, once enjoyed a vast area of distribution ranging from Vembanad lake in Kerala through the estuaries on the east Coast to the Sundarbans of West Bengal.
Now the species has depleted seriously due to hunting and loss of habi­tat. By 1974 it was known that they have become extinct from Kerala, Tamil Nadu and Andhra Pradesh. A few existed in the Brahmani – Baitarini deltaic area of Orissa, known as Bhitar kanika and also a few in the Sundarbans of W. Bengal.
Mugger or Marsh crocodile (C. palustris), the species was once common in the jheels, rivers, reservoirs, irrigation canals and. lakes. By 1974 it had become a rare species and seriously depleted in U.P., Bihar, M.P. and W. Bengal, and in South India (Tamil Nadu, Karnataka and Andhra Pradesh) the population had been hard hit, though not rare.
Gharial (Gavialis gangeticus) was abundant in the Ganges, the Mahanadi and the Brahmaputra river systems. By 1975 survey, it was known that the population on the Mahanadi River in Satkoshia Gorge was 5 and in the rivers of U.P., M.P., and Rajasthan revealed the numbers of about 35.
List of Rare and Endangered Species:
Indian reptilian fauna is represented by tortoises terrapins and turtles (Chelonia), lizards and snakes (Squamata), and crocodiles and gharials (Crocodilia). Reptilian species has become deple­ted for meat, egg, skin, shell, bones, fat and venom.
Endangered chelonians are the green turtle (Chelonia mydas agassizii), the leatherback turtle (Dermochelys coriacea schlegelii), the hawk bill tur­tle (Eretmochelys imbricata bissa), the olive ridley (Lepidochelys olivacea), and loggerhead turtle (Caretta caretta gigas).
They are found in both coasts of the subcontinent. Othr tortoies belonging to the families Emydidae and Trionychidae are box tortoise (Batagur baska), Indian tent turtle (Kachuga tecta tecta), North Indian flap-shell turtle (Lisemys punc­tata punctata), Ganges soft shelled turtle (Trionyx gangeticus) and peacock marked soft shelled turtle (Trionyx hurum).
All the monitor lizards are recognised as threatened species. They are the common Indian monitor (Varanus bengalensis), the water monitor (Varanus salvator), the yellow monitor (Varanus flavescens) and the desert monitor (Varanus griseus).
Among snakes Python molurus and Python reticulatus are recognised as endangered species. The Indian egg-eating snake (Elachistodon westermani) is a rare species found along the Himalayan foothills from Kumayun east to Arunachal Pradesh.
All the three Indian species under the order Crocodilia are endangered, i.e., the estuarine crocodile (Crocodylus porosus), the marsh crocodile (Crocodylus palustris) and the gharial (Gavialis gangeticus).
Different Categories of Rare Animal Species:
The International Union for conservation of Nature and Natural resources (IUCN) has recognised the following categories of rare animals.
A taxon is regarded as “extinct” when there is no doubt that its last member has died.
Extinct in the Wild:
A taxon is “Extinct in the Wild” when it is known only to survive in captivity, in cultiva­tion or as a natural population outside the past range. Example: some species of Partula snails.
A taxon is “Critically Endangered” when it is facing an extremely high risk of extinctirl in the wild in the immediate future.
Dancing deer or Brow-antlered deer of Manipur.
Taxa in danger of extinction and whose survival is unlikely if the causal factors contin­ue operating. Included are taxa whose numbers have reached to a critical level and they are deemed to be in immediate danger of extinc­tion.
Taxa likely to move into the endangered category in the near future if the causal factors continue operating. Included are taxa, of which most or all the populations are decreasing due to over- exploitation, habitat destruction or other envi­ronmental disturbances. Taxa with populations that have been seriously depleted and security is not yet assured.
Taxa with small populations in the world that are not at present endangered or vulnera­ble, but are at risk.
A taxon becomes a “Lower Risk” when it has been evaluated and does not qualify for any of the following categories, such as (i) Critical (ii) Endangered (iii) Vulnerable or data deficient.
Black buck (Antilope cervicapra).
Those species which are in one of the three categories, i.e., endangered, vulnerable or rare.
The information is not enough to say which of these three categories is appropriate in case of threatened species.
Taxa which were formerly included in one of the above categories, but now consider relatively secure due to effective conservation measures or the previous threat to their survival has been removed.
Taxa that are doubtful to be placed in one of the first three categories but for which insufficient information is currently available.
Class Reptilia - Reptiles
The Class Reptilia includes the snakes, lizards, crocodiles, and turtles of the world. There are almost 10,000 species of reptiles on the planet lumped into a single class known as Reptilia. They are then broken up into the following groups:
Notice how birds somehow fall into this phylogenetic tree. Even though most traditional models of classification will put birds in their own class, they should probably be listed in with the other reptiles because of their common ancestory.
What makes a reptile?
As a general rule, reptiles are egg-laying (oviparous). As with many other classifications, there are a few exceptions. A few snakes retain their eggs until hatching, and a few are viviparous. Reptiles breath air, unlike fish. They are also ectothermic (cold-blooded). Most also have skin covered in scales and/or scutes.
How to be a Herpetologist
So you want to be a herpetologist? That is an admirable choice, but you should have a strong desire to study reptiles and amphibians for the road to a career in herpetology is not an easy one — but it is an interesting one. Below is a description of how to become a herpetologist, originally written in 1985, but still very relevant today! In addition, here some some links to other helpful resources:
What is a Herpetologist and How Can I Become One? by Drs. Whitfield Gibbons and Michael Dorcas
Careers in Herpetology
In reality, herpetology is a sub-field of biology. Jobs in biology traditionally fall into four areas: college and university employment, government work (including state and federal), medical related work, and zoological park or museum staff. More recently, industrial and medical biotechnology have emerged as areas with new and exciting opportunities for biological research. What all of these jobs have in common is training in a biological field. The herpetological emphasis is put there by the worker! For example, a person might be trained in ecology and do environmental impact studies for the government. If that person is also a herpetologist, reptiles and amphibians might be the animals studied to evaluate changes in the environment. A medical research with training in hematology might, if interested in herpetology, study blood of reptiles and amphibians. It is rare to find a job that considers someone to be a herpetologist first!
Years ago it was possible for individuals to study amphibians and reptiles on their own, perhaps by maintaining large collections of animals or by studying them in the wild, and learn enough to get a position at a zoo or museum as a herpetologist. Today, however, techniques for conducting nearly any biological study have become so sophisticated, and competition for jobs has become so intense, that a college degree is a necessity in order to pursue a career in herpetology. Often an advanced degree (masters or doctorate) in biology, anatomy, biochemistry, microbiology, physiology, or some related field is required for almost any specialized job. Many, if not most, herpetologists today are employed at colleges or universities and an advanced degree is usually a condition of employment at such institutions.
The specific training required for a career in herpetology varies according to one’s goals. In virtually all cases a bachelor of arts or a bachelor of science degree with a major in biology is required. Courses in inorganic chemistry, organic chemistry and biochemistry, calculus, physics and/or earth science should be taken. Statistics is now a necessary tool in biological studies and courses in this area are essential. A great deal of herpetological research is conducted in other countries and facility in one or more foreign languages allows one to follow such activities in other nations. As in other branches of science, computer literacy is indispensable and students should enroll in courses that provide training in computer use.
Any college that provides a strong background in the sciences, mathematics and English also provides the basis for a career in herpetology. But if you are seriously interested in pursuing herpetology as a career you might want to attend a college that also offers a course in herpetology (or at least in natural history or vertebrate zoology) and has one or more faculty members conducting herpetological research. “Leads” to such institutions can best be obtained by studying several recent issues of herpetological journals such as Journal of Herpetology, Herpetological Review, Copeia, or Herpetologica, and noting where some particularly interesting research (to you) is being conducted. You can then write to the institutions or authors and ask for further information about their programs. Another reason to look at herpetological journals, which may be found in college or natural history museum libraries, is to give you some idea of the broad scope of herpetological research and to help you narrow down your interest.
Following graduation from college with a bachelor’s degree in biology, you may want to seek employment immediately. However, opportunities for employment with only a bachelor’s degree are limited, both in terms of available positions and level of advancement. Nevertheless, many graduates obtain jobs in museums or zoos working with exhibits and live animals and dealing with the public. Others work in research laboratories assisting investigators with their projects such positions exist at larger colleges and in certain government agencies. Students with a broad interest in natural history may find jobs in local, state, or national parks (as park naturalists) or certain large companies as environmental specialists a knowledge of herpetology can be particularly useful in these positions. In addition, there are many fields — veterinary assistant, biomedical salesperson, biology teacher — where positions less herpetologically related are also available.
Students who continue their education through to the masters or doctorate degree usually find employment where they have greater freedom to pursue their own interests, the salary is higher, and the responsibilities are greater. Most individuals with a Ph.D. work at a college or university where they teach and conduct research in their own area of interest. Herpetological research is often conducted in the field, which involves the collection, marking or observation of organisms, or the analysis of environmental conditions associated with particular populations. However, other herpetologists have a strong interest in laboratory research and spend little time in the field. Studies in physiology, immunology, embryology, genetics, anatomy, and biochemistry are usually conducted in a laboratory, while research in ecology, behavior, population biology, systematics, reproductive biology, and biogeography involve significant amounts of field work. In all cases, however, data have to be analyzed, summarized, and eventually published in a scientific journal. The goal of herpetological research, as with other branches of biology, is to learn as much as possible about our special interest and to communicate this knowledge to others. Publication of this research in journals is how scientific knowledge is communicated and most employers look for people who have shown an ability to do research and also to publish it. Developing writing skills should therefore be considered a must in college.
The main thing is — if you want to be a herpetologist, try it! The study of animal biology can be a continuing interest and challenge for the rest of your life, and it will serve you well no matter what career you ultimately choose.
Herpetology as a Career was written in 1985 by a committee composed of:
Henri C. Seibert (Chairman)
Department of Zoological and
Athens, Ohio 45701, USA
Ralph W. Axtell (SSAR Pres., 1983)
Department of Biological Sciences
Southern Illinois University
Edwardsville, Illinois 62026, USA
Neil B. Ford
Department of Biology
University of Texas
Tyler, Texas 75701, USA
Martin J. Rosenberg
Department of Biology
Case Western Reserve University
Cleveland, Ohio 44106, USA
This page was initiated on 13 April 1998. Of course, we do not expect that it will answer all your questions, or that it will answer your questions completely. But it should provide many answers, and as always you are encouraged to contact us with additional questions.
Frequently Asked Questions (FAQ)
Where can I find schools that offer a degree that includes course work in herpetology?
There is a partial [and somewhat outdated] list at http://www.anapsid.org/univ.html that will get you started. But one of the best ways is to use a major search engine and plug in the words herpetology course. You can also add a state name, etc to refine your search. We are in the process of building a database, and will make it available when it gets to a useful size.
Do I absolutely need a graduate degree (Masters or PhD) to do research in herpetology?
To do herpetological research as a university faculty member or museum curator presently requires a PhD and usually a history of successful grant-writing. However, there are a fair number of persons doing high-quality, accepted research in herpetology who have no higher degree. They are scholars in every sense of the word who are self-taught, and who went out and collected animals, made careful observations, read a lot, and talked to others at professional meetings. One of the leading authorities on Mexican herpetology is a pharmaceuticals salesman in Louisiana. One of the leading authorities on Kansas (USA) herps, just now retired, never finished college. And, one of the world’s authorities on the breeding biology of pythons is a young fellow in Oklahoma (USA) who has managed to make a fine living out of breeding them commercially. But note that the emphasis of this section is jobs in herpetology doing good research does not guarantee a salary for it!
What kind of benefits does a herpetologist get? Do you get medical and dental benefits, and retirement?
These things depend upon your employer and are very variable.
What’s the best way for a high school (or younger) student to begin to prepare to investigate herpetology as a career?
It is important to begin to cultivate contacts through joining any State herpetological society or similar groups. Many have Web sites. Membership typically is a broad cross-section of society — persons with jobs in diverse fields, who share an interest in herpetology. Some members almost surely will be university faculty others may work in State non-game wildlife programs some will be students others will be interested hobbyists with no job-link to herpetology at all.
Also, you should, in high school, take a well-rounded set of courses (emphasizing sciences) that will qualify you for admittance to a good, 4-year college, in which you should major in what generally is called “organismic biology” or some synonym for that which distinguishes it from “cell and molecular.” Your GPA will be important competition can be fierce! I know of no undergraduate program that offers herpetology as a sole concentration it simply is too narrow a field, though at many schools a herpetology COURSE or two will be offered. A Bachelor’s of Science degree would be appropriate.
How can a person, who because of young age or lack of formal schooling, learn about reptile and amphibian behavior other than by reading books?
Don’t ignore reading as a source of knowledge! Books and scientific journals contain a wealth of information unavailable on the Web. Keeping herps as pets is an enjoyable way to observe habits and get to know species, but it has its own drawbacks in that care is constantly required, even when on vacation or off to college (some species live a LONG time!). It can be as useful (maybe more), if there is a nearby good-quality zoo, to volunteer some Summer time to help do cleaning or be a “gofer” in the reptile department. Do not expect to be allowed to work with live animals at once zoo policy or insurance regulations may in fact prohibit non-employees from so doing. But, one can learn a great deal this way, as well as expand one’s contacts. And, sometimes good-quality volunteer work can lead to a paying job. Volunteer work should be planned as a regular part of the week, so supervisors know they can depend upon a volunteer showing up, even if for a couple of hours MWF (or whatever all agree is useful). Volunteering to help a college faculty member with research interests can be a similarly good experience that allows a lot of learning as a benefit.
15.9: Classes of Reptiles - Biology
Reptiles are animals from the class Reptilia.
There are 4 orders of the class Reptilia:
- Chelonia – Turtles and Tortoises
- Crocodilia – Alligators, caimans, crocodiles, gavials
- Rhynchocephalia – tuatara
- Squamata – amphisbaenians, lizards, snakes
General Characteristics of Reptiles:
- Reptiles have a backbone. They are vertebrate animals just like mammals and birds.
- Reptiles are covered in dry scales made of keratin, the same protein that makes up mammal hair and bird feathers.
- Reptiles breathe air with lungs, the same as mammals and birds.
- Most reptiles lay eggs on land. Some reptiles give birth to live young.
- Most reptiles do not protect their eggs or young. Crocodilians, some snakes, and a few lizard species do protect their eggs and to some extent their young.
- Most reptiles are cold-blooded or ectothermic meaning, “outside temperature.” This means the animal’s internal temperature changes with the temperature of the environment. Mammals and birds are endothermic meaning their temperature is regulated from within their own body.
Chelonians – Turtles
There are over 300 different kinds of turtles. Sea turtles swim through the warm oceans of the world with giant flippers, tortoises lumber across the land with strong elephant like legs, and terrapins paddle with webbed feet in freshwater habitats.
A turtle’s ribs and backbone form its hard shell. Covered in skin and scales, a turtle’s shell is considered and endoskeleton, just like a human’s skeleton.
Sea turtles can hold their breath for over an hour by using the powers of their amazing heart. The heart blocks off blood to the lungs and allows the blood to travel to only parts of the body needing oxygen while under water!
The giant galapagos tortoise, aldabra tortoise, and african spurred tortoise can live to be over 170 years old!
Crocodilia – Crocodiles and family
With toothy smiles and big strong tails, crocodilians number over 20 different species including crocodiles, alligators, caimans, and gharials. Gharials have very long, narrow snouts studded with sharp teeth.
Crocodiles and alligators are a bit more difficult to tell apart. Alligators typically have broader snouts and straight rows of ridges down their backs. Crocodiles have narrower snouts and irregular rows of ridges on their back. When a crocodile’s mouth is closed, its fourth tooth on the lower jaw fits into a notch on the outside of the upper jaw.
There are only two different kinds of alligators the American alligator and the endangered Chinese alligator.
Crocodilians feed on insects, snails, shellfish, frogs, turtles, fish, mammals, and birds. Most crocodilian species are afraid of humans and will swim away when people are nearby. The large saltwater and Nile crocodiles are the exceptions – they have been known to attack humans.
Crocodilian eyes and nostrils are located on top of their head to allow them to see and breathe above the water’s surface. They are covered in bony armor to protect them from both their prey and predators. They are very well built to survive in their watery habitats.
We still have much to learn from crocodiles. We have found they are immune to some diseases, heal quickly, are intelligent, and are wonderful parents. Alligators even help other animals survive during droughts by digging water holes with their huge body. Sadly, many crocodilian species are endangered due to habitat loss and over-hunting for food and the skin trade.
It is interesting to note that crocodilians are more closely related to birds than lizards. The superficial resemblance of crocodilians to lizards is due to convergent evolution.
Rhynchocephalia – Tuatara
The tuatara is an unusual reptile unchanged since the days of the dinosaurs. Although they look much like lizards, tuataras have different skulls, teeth, and pelvic bones. Living only in New Zealand on a few protected islands, these reptiles prefer lower temperatures than other reptiles. Tuataras live for a long time, probably over 100 years!
Unfortunately, they are highly endangered due to habitat loss and introduced predators.
Squamates (Amphsbaenians, Lizards, & Snakes)
Scientists do not separate lizards and snakes or the strange amphisbaenians into groups, but classify them all in one order.
Amphisbaenians look a little like big worms, but like all reptiles, they have an internal skeleton made of bone and they are covered in dry scales. They are long and usually legless (although some have two front legs and no rear legs.) They are primarily fossorial, meaning they spend most of their lives underground.
Lizards are the most diverse group of reptiles. They come in a huge variety of colors, shapes, and sizes. Some lizards, such as the Komodo monitor (dragon), can grow over 10 feet long. Others, like the Jaragua lizard, are able to curl up on a dime.
A typical lizard has external ears, four legs, claws, eyes with eyelids, and tails. Scientists have found that lizards can see color, and some can even see in the ultraviolet wavelengths. Excellent eyesight allows the creatures to snatch bugs out of the air and to see spectacular mating displays.
A lizard’s sense of smell and taste is very acute. Monitor lizards even have a forked tongue like a snake to enhance their ability to smell.
Lizards have found remarkable ways to survive. Many are covered in spines, some can stick to trees, most are able to lose their tails and grow them back, others change colors, a few glide out of trees, and one species can even run across water!
Compare and Contrast: Snakes vs. Lizards
- All snakes are legless, but some lizards are legless too!
- All snakes have no ears, but some lizards lack ears as well.
- All snakes lack eyelids, but some lizards also lack eyelids.
- Snakes have forked tongues, but so do many lizards.
Confused yet? Don’t worry, from now on we will discuss snakes and lizards as separate groups. Whew! (and you were worried)
Snakes are one of the most misunderstood group of animals on our planet. Many people fear snakes because of the myths and falsehoods perpetuated by the media and our society. Learning about snakes is a great way to overcome fears about snakes.
Snakes are reptiles that have no legs, ears, or eyelids. Snakes are dry, not slimy, as their scales are made of keratin, the same protein human hair and fingernails are made of.
A snake’s forked tongue cannot sting or hurt you. A snake that is constantly flicking out it’s tongue is simply interested in its surroundings, kind of like the “sniffing’ of a dog. Chemicals in the snakes surroundings, or “scents patricles,” stick to the tongue as it waves it around. Then the scent laden tongue deposites these particles onto a tissue pad on the floor of the mouth and that tissue pad is then pressed to the roof of the mouth transferring particles to the vomeronasal organ (a small hole in the roof of the mouth) sending instant messages about what it detects to the brain.)
Remarkable heat sensing pits light up the night for some lucky snakes. Rattlesnakes, pit-vipers, copperheads, boas, and pythons are able to distinguish in vivid detail differences in temperature allowing them to navigate and catch prey in complete darkness.
All snakes are carnivores. To catch prey, a snake must either bite it with fangs and inject venom, or use its body to subdue the animal using strong muscles. Swallowing the food is a challenge for an animal with no arms or legs! Their jaws are not strong enough to chew their food. Tiny curved teeth hook on to the food item, and allow it to only go in one direction, down the throat!
A snake’s head may appear too small to swallow many food items. Snakes can open both their upper and lower jaws exceptionally wide. The lower jaw includes two jaw bones connected in the middle with a stretchy ligament, so the mouth can open wide sideways as well. One side of the jaw holds the prey while the other side of the jaw slides forward, walking the food further into their mouth.
The largest snakes in the world are the anaconda and reticulated python, both able to grow up to 30 feet long and weigh several hundred pounds.
Snakes benefit our us and our planet in many ways. Snake venoms are used to make medicine to treat cancer, heart disease and other illnesses. Snakes prey on rodents, insects and other agricultural pest species. Other species of animals, including eagles, rely on snakes as food sources. Snakes are natural and integral part of our world’s ecosystems. If you see a snake, just leave it alone.
This is all a matter of how we define terms, and which definitions are scientifically useful.
Traditionally (since Linnaean times), organisms were classified based on their outward similarities (phenetic systematics). As such, the traditional definition of reptile, which is the same as any common usage that I've heard, includes organisms like snakes, lizards, turtles and crocodiles but does not include birds. This is the class Reptilia. As evolutionary understanding increased, however, it was found that some reptiles, like crocodiles, are actually more closely related to birds than to other reptiles. This makes the common use of reptile a paraphyletic classification.
In modern phylogenetic systematics, organisms are classified in monophyletic groups, or clades, that include an ancestor and all of its decedents (ie it is based on evolutionary relationships). Thus the class Reptilia, since it is paraphyletic, is essentially meaningless in this system. In order to have consistent nomenclature, you could either say that birds are reptiles (a new, cladistic meaning of the term, but which contradicts traditional/common usage) or come up with a new name that includes all traditional reptiles and birds. Taxonomists taking the latter approach use the term Sauropsida for this clade. Sauropsida does not have a taxonomic rank like class because such ranks are useless in cladistics (and actually quite arbitrary even in the traditional system).
So, to specifically address your question:
In phenetics, both Reptilia and Amphibia have the taxonomic rank of class.
In phylogenetics, what we commonly consider reptiles and birds are grouped in a single clade that can be called Sauropsida or Reptilia (re-defined to include the clade Aves) depending on who you ask or which paper you read. Amphibia form a clade.
Perhaps the most important take-away message is that taxonomy is largely un-standardized.
The accredited reptile courses that we offer will give students who own reptiles or who have a general interest in this fascinating species a better understanding of their origins and biology and of the care and welfare issues that affect reptiles kept in captivity. Careers working with reptiles are varied and include working in zoos, safari parks, education, veterinary, conservation and for animal charities dealing with the rescue, care and re-homing of many different types of reptiles. The 2 module reptile certificate courses take an average of 2 months to complete. Students will gain a good understanding of how to improve the quality of life of reptiles in captivity by providing the right care including adequate housing and environmental enrichment to reduce boredom, stress and behavioural problems.
Reptiles are becoming one of the most common exotics kept in captivity as pets. Unfortunately an increasing number are being handed into rescue centres in a poor condition through lack of proper care. Some jobs working with reptiles involve working in pet shops that sell reptiles. There is strong feeling from many animal rescue centres, who have to handle difficult situations with the ever-increasing tide of unwanted animals, that whilst pet shops may be the best places to buy supplies such as equipment and pet food, they are unfortunately frequently responsible for people making impulsive decisions about getting a pet and increasingly reptiles are being sold by some pet shops as ‘easy to care for’ pets. There are many sad stories of reptiles being bred purely for profit and sold to pet shops where they can be and frequently are, bought on impulse by anyone. Reptiles require specialised care and are prone to severe health problems if they are not cared for properly. Apart from the suffering endured, a sick animal can cause problems for the pet shop owner who has to deal with angry and upset customers as well as pay for the animal to be treated.
Reptiles & Amphibians Science Projects
One practical way to see for yourself how an amphibian and reptile differ is to compare the anatomy of two species, such as a frog and a snake. Although you can observe the external anatomy on live ones at a pet store or in the wild, it’s hard to discover anything about their insides without doing a dissection.
Even if you don’t want to dissect a snake (or a turtle, for another interesting reptile specimen), you might find the following description of a snake’s anatomy helpful. You can compare it to our online frog dissection guide, with pictures and detailed instructions. (You can also find virtual frog dissections online, instead of doing your own.) This is an ideal project for junior high and high school students who are studying animal classification.
Click this link for a printable snake dissection diagram with labeled parts (.pdf). Use this as a guide for locating organs.
- Inspect the external anatomy of the snake. Why do you think the scales on the specimen’s back (dorsal side) are different than the scales on its belly (ventral side)? The ventral scales correspond to the number of ribs that the snake has and allow greater flexibility of movement.
- Make a long incision down the center of the ventral surface, from the cloacal opening to the throat. Carefully pull back the skin and pin it down on either side, cutting the membrane layer underneath as necessary. Once the snake is opened, observe how it looks inside. Then slice the membrane away until it separates from the organs. (This membrane holds the organs securely in place in the living snake.) This is the longest part of the dissection process, but go slowly and cut carefully.
- Identify the major organs listed below. The heart, stomach, gallbladder, liver, and large and small intestine will probably be the easiest to find. These are listed in order roughly from head to tail.
Trachea: A dark-colored tube in throat that brings air to the lung.Heart: Located just below trachea. It is a three-chambered like a frog heart.
Right lung: Most snakes have only one functioning lung, a long narrow sac starting near the heart. Look for it between the liver and stomach. The specimen might also have another, smaller lung.
Liver: A long, thin orangish-colored organ on the left side (as you look at it).
Stomach: A long sac that connects to the esophagus in the throat and small intestine lower down. Is your specimen’s stomach empty or full? If full, you might want to check out the contents to discover what the snake was eating.
Gallbladder & pancreas: The gallbladder is small and round, usually greenish-colored from the bile for digestion stored in it. You might have to remove some of the yellow fat bodies to see it. (A healthy snake will have many fat bodies.) The pancreas looks just like an extension of the intestine, right next to the stomach.
Small & large intestine: The small intestine starts right below the stomach and forms many coils.
Gonads: These might look similar to the intestine, but are not connected to it. Male snakes are identifiable by testes inside and hemipenes at the cloacal opening. Females have a pair of ovaries and might have eggs. (If both the frog and snake specimens have eggs, be sure to compare them!)
Kidneys: These are located near the end of the large intestine they should be similar in color to the intestine, but if you look closely you’ll see that they are a different kind of tissue.
Print out this diagram and fill in the labels yourself to test your knowledge of snake anatomy:
See our other free dissection guides with photos and printable PDFs. Click here
Comparing Frogs & Snakes
How do you tell the difference between a reptile and an amphibian? To help your young children understand the similarities and differences between reptiles and amphibians, make a chart. For older elementary and junior high kids, let them create charts listing differences between different kinds of reptiles or amphibians (e.g., how is a frog different from a salamander?).
Since reptiles and amphibians can be hard to observe in the wild, take a field trip to a zoo or pet store. You might call ahead to see if your kids will be allowed to handle any of the animals. Before you go, ask younger kids what they think a snake feels like. What about a frog? A turtle? Will a frog or a snake feel more ‘slimy’? After the visit, discuss the experience. Encourage older kids to investigate feeding habits, make sketches, observe how the animal moves, etc.
If you are handling frogs in the wild, be sure that you have wet hands or hold the animal with a plastic bag. Your bare hands can quickly cause the frog’s skin to dry out. After touching any amphibian or reptile, be sure to wash your hands well with soap and water!
To find out more about frogs, do research on one of these topics: what kinds of frogs live in your area? Can you find more than one species of tadpole locally? If so, compare them. What do local frogs eat? How would the mosquito population be affected if there were few or no frogs in a swampy region? Pick a frog or frog characteristic that is interesting to you, and see what you can find out about it. Look for close-up frog pictures in a magazine like National Geographic or on a website.
To see for yourself how an amphibian and reptile differ, compare the external anatomy of two species such as a frog and a snake. You can observe the external anatomy of live ones at a pet store. Or do an online image search: try ‘bufo’ (part of the scientific name for some frog species), ‘bullfrog,’ ‘poison dart frog,’ ‘tree frog,’ ‘garter snake,’ ‘elipidae’ (the main family of poisonous snakes), ‘colubridae’ (the family with common snakes), and ‘boidae’ (constrictors).
Want to really dig in? Try a frog dissection! Dissections are a great way to see an animal’s internal anatomy up close, and we provide a variety of frog specimens to explore and learn from:
This is just an overview of some features of frogs and snakes – there’s a lot more to learn about them!
- Skin: How does the skin of a frog look (and feel) compared to a snake or other reptile? One is typically smooth and moist, one is dry and scaly. Frogs can exchange oxygen and carbon dioxide through their skin. They have mucous glands that secrete a waterproof coating to keep their skin moist and slippery. Snakes have a tough coating of scales made of keratin, the same protein that forms your hair and fingernails. Each species either has smooth scales or rougher keeled ones, with a unique pattern of scales and coloring. They also have long horizontal scales on their belly that help them move across surfaces.Both frogs and snakes (as well as other reptiles) molt, or shed their skin. Frogs change their skin about once a week! Although all reptiles shed their skin as they grow, snakes lose their skin in a whole piece rather than pieces flaking off.
- Head & mouth: Sensory organs on frogs and snakes differ quite a lot. Frogs have bulging eyes that provide them a wide range of view. Snakes, on the other hand, generally have poor vision.
Frogs have a tympanic membrane that can detect sound waves in water or the air and transfer the sound to the inner ear. Snakes have no external ear openings, but they can pick up vibrations through their jaw bones, which transfer to their internal ear bones.
Frog tongues are broad and specially attached so they can be thrust out and catch insects. Snake tongues are narrow and forked, to ‘taste’ chemical particles in the air.