Reptiles: Origin, History and Classification

In this article we will discuss about Reptiles:- 1. Definition and Origin of Reptiles 2. History of Reptiles 3. Characteristic Features 4. Classification.

Definition and Origin of Reptiles:

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.

Origin:

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, ’56, ’66), Colbert (1951, ’62, ’65), Coin and Coin (1962), Eric Worrel (1963), Bellairs (1970), L. M. Kianber (1972), Bellairs and Attridge (1975), Carl Gans (1969-’79), 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).

8. No lateral line organs.

B. Internal Characters:

(a) Soft Parts:

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.

(b) Hard Parts:

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.

C. Embryology:

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.

3. Meroblastic cleavage.

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.

D. Physiology:

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.

Examples:

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).

Order 2. Mesosauria:

(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.

Example: Mesosaurus.

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.

6. The tail is short.

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.

The aortae are:

(i) Pulmonary arch

(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:

(i) Gastric artery,

(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.

Remarks:

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).

Habitat:

They are found in terrestrial, aquatic (ponds, lakes, marshes, reservoirs, estuaries and rivers) and marine environments.

Diet:

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.

Longevity:

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.

Speed:

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.

Intelligence:

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.

Courtship:

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.

Carapace:

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.

Plastron:

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.

Example:

Pelomedusa.

Family 2. Chelyidae (Snake necked turtles) of South America, Australia and New Zealand.

Head and neck not completely retractile under the shell.

Example:

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):

Tail short.

Family 2. Platysternidae (Fresh water forms of Southern Asia).

Head large and tail long; hooked mandible.

Example:

Platysternum.

Family 3. Chelydridae (Snapping turtles) of North and Central America.

Head and neck large, cannot be withdrawn under shell; long tails; upper jaw hooked.

Examples:

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.

Example:

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.

Example:

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.

Example:

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.

Examples:

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.

Example:

Leather back turtle (Dermo­chelys coriacea, Fig. 8.51 G)

Family 9. Carettochelyidae:

Limbs paddle-shaped; shell soft.

Sea Turtles in India:

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.

Turtle Conservation:

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.

Example:

Araeoscelis.

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.

Examples:

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.

Examples:

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.

Example: Youngina.

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’.

A. External Features:

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.

3. It weighs about 1 kg.

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).

B. Hard Parts:

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.

These are:

(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.

C. Soft parts:

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.

About the species:

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.

Geographical distribution:

Present:

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.

Past:

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.

The similarities are:

(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,

(2) Immovable quadrate,

(3) Abdominal ribs and uncinate pro­cess,

(4) Ectepicondylar and entepicondylar foramina in the humerus and

(5) 10 bones in the carpus.

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.

With Dinosaurs:

(a) Similarities:

(1) Skull is of diapsid type and the quadrate is fixed.

(2) Presence of unci­nate process and abdominal ribs.

(b) Dissimilarities:

(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.

Remarks:

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.

B. With Crocodilia:

(a) Similarities:

Both in Sphenodon and Crocodilia:

(1) The quadrate is immovable.

(2) Pro-atlas is present.

(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.

(b) Dissimilarities:

(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.

C. With Chelonia:

(a) Similarities:

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.

(5) Pecten is absent.

(b) Dissimilarities:

(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.

Remarks:

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.

D. With Lacertilia:

(a) Similarities

In both Sphenodon and Lacertilia:

(1) General body plan is identical.

(2) Some Geckos amongst the Lacertilia pos­sess amphicoelous vertebrae.

(3) Pro-atlas is present.

(4) Caudal vertebrae are separated by septum.

(5) Remnant of notochord is present between the vertebrae.

(6) Ribs are single- headed.

(7) Chevron bones are present.

(8) Parietal organs are found.

(9) Cloacal glands are present.

(10) Oviducts open dorsally.

(b) Dissimilarities:

(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.

Remarks:

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.

E. With Amphibia:

(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.

Remarks:

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:

1. Gunther (1867):

Sphenodon is the sole representative of an order of modern Reptilia, called Rhyncho­cephalia which equals in rank to other living orders.

2. Gadow (1901):

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.

3. Newman (1939):

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.

4. Weichert (1958):

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.

5. Young (1981):

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.

10. The brain is small.

11. Organ of Jacobson is well-developed.

12. Distribution is cosmopolitan.

The Order squamata have 3 Suborders:

(i) Lacertilia

(ii) Ophidia and

(iii) Amphisbaenia.

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.

4. Tympanum is distinct.

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.

Example: Corytophanes.

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.

Example: Crotaphytus.

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]:

Example:

Tropidurus.

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.

Examples:

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]:

Examples:

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.

Examples:

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.

Examples:

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.

Examples:

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.

Example:

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.

Example:

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.

Examples:

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.

Reproduction:

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.

Food:

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.

Longevity:

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.

Number:

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.

Examples:

Indian Rock Python (Python molurus), Red Sand Boa (Eryx johni), Boa (Boa con­strictor).

Geographical distribution:

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.

Example:

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.

Examples:

Common Indian worm snake (Typhlina bramina); Beaked Indian blind snake (Typhlops acutus).

Geographical distribution:

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.

Geographical distribution:

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.

Examples:

Ocellate Uropeltid (Uropeltis ocellatus); Travancore Shield-tail (Rhinophis travancorius).

Geographical distribution:

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.

Example :

Xenopeltis unicolor.

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.

Examples:

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).

Geographical distribution:

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.

Examples:

Indian egg eater snake (Elachistodon westermanni), African Egg-Eater (Dasypeltis).

Geographical distribution:

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.

Examples:

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.

Geographical distribution:

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.

Example:

Sea snake (Hydrophis caerulescens); Hook nosed sea snake (Enhydrina schistosa).

Geographical distribution:

Tropical seas.

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.

Example:

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).

Geographical distribution:

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.

Distribution:

Worm lizards are confined to mainly South America, Mexico, West India, South Western United States, Africa and Southern Europe.

Examples:

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).

Examples:

Euparkeria, Orninthosuchus, Phystosaurus.

Order 2. Crocodilia or Loricata (Tri.—Rec.) [L. crocodilus = a crocodile; L. loricatus = clad in mail.] 21 species:

Crocodilian Evolution:

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.

Characteristic Features:

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.

Origin:

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.

Habitats:

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.

Geographical distribution:

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.

Species:

The living crocodilians represent 7 genera and 21 species.

Sex determination:

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).

Reproduction:

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

(iii) Gavialidae (ghariais).

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.

Examples:

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.

Examples:

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.

Examples:

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.

v) The limbs were short.

Examples:

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.

Examples:

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.

Indian Species:

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);

(ii) Dasia (1 species);

(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);

(x) Chalcides (1 species);

(xi) Barkudia (1 species).

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.

Extinct:

A taxon is regarded as “extinct” when there is no doubt that its last member has died.

Example:

Indian cheetah.

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.

Critically Endangered:

A taxon is “Critically Endangered” when it is facing an extremely high risk of extinctirl in the wild in the immediate future.

Example:

Dancing deer or Brow-antlered deer of Manipur.

Endangered:

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.

Vulnerable:

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.

Rare:

Taxa with small populations in the world that are not at present endangered or vulnera­ble, but are at risk.

Lower 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.

Example:

Black buck (Antilope cervicapra).

Threatened:

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.

Out of danger:

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.

Indeterminate:

Taxa that are doubtful to be placed in one of the first three categories but for which insufficient information is currently available.

Data deficient:

A taxon is “Data Deficient” when there is inadequate information to make direct or indi­rect assessment for its risk of extinction, e.g., seven spotted cockroach.