The following points highlight the nine most common lizards found in World. The lizards are: 1. Hemidactylus 2. Calotes 3. Draco 4. Iguana 5. Phrynosoma 6. Chamaeleon 7. Varanus 8. Heloderma 9. Ophisaurus.
Lizard # 1. Hemidactylus:
Hemidactylus (Fig. 24.4) is commonly known as wall lizard or house lizard. It is found in homes in India, Africa, Sri Lanka and China. Other genera are common all over the warmer countries. It is not a lover of sunshine. It is about 25 cm long, of pale-green colour. Head is broad and fiat, ear opening is vertical, tail is moderately long, scales are minute and smooth. It has a short, sticky, slightly notched tongue with which it feeds on insects at night.
The digits are dilated with a double series of ridged lamellae on the ventral side. They have sharp claws, which enable the lizard to walk on ceilings and smooth surfaces. The tail can break off at an unossified part of caudal vertebrea.
The broken part of the tail wriggles actively to distract a predator, while the lizard escapes. The tail regenerates, but the new tail is not exactly the same as the old one because the lost vertebrae are not regenerated. Hemidactylus is one of geckos which are the only Squamata which lay round hard-shelled eggs, in all others the eggs are leathery. Male has femoral pores on the thighs.
Lizard # 2. Calotes:
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Calotes versicolor is commonly called garden lizard or girgit. It is also known as blood sucker because of the red colour of the throat. It is found in India, China and Malaysia and is an arboreal insectivorous agamid, as also Uromastix. It is about 30 cm long and has coarse rough scales. The tail is very long and slender. There is a crest of sharp spines on the neck and back.
The Indian Calotes versicolor is known for its colour changes, the normal colour is olive-green but in courtship or threat the body becomes yellow, and the neck and sides of the head become red. Colour changes are due to temperature and environment. The colour is present in melanophores of the skin which are controlled by hormones of the pituitary.
It has no gular sac found on the neck in some species. It nods its head up and down. Body is covered with strongly keeled scales. The tail does not break. It lives on trees and is insectivorous and oviparous.
Lizard # 3. Draco:
Draco (Fig. 24.4) is commonly called flying dragon or flying lizard. The body is compressed dorso-ventrally, on the neck are three soft hooks. Teeth are acrodont. Five or six ribs on each side of the body are elongated and support a wide fan-shaped flap of skin between the fore and hind limbs.
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When ribs are raised, the skin is stretched to form wing-like parachutes which enable the lizard to glide downwards from branch to branch but does not fly. The hooks on the neck help in alighting on branches. Draco is arboreal and beautifully coloured like the flowers of trees in which it lives. It is insectivorous and is found in the Indo-Malayan peninsula. Draco volans is found in Sumatra, Java and Borneo. Draco dussumieri occurs in Chennai.
Lizard # 4. Iguana:
Iguana (Fig. 24.4) is a lizard of South and Central America and West Indies. It has a laterally compressed body and long tail. It is about 2 metre long. Along the dorsal side of the neck and body is a crest of long spines.
On the throat is present pendulous and expansible folds of skin which play a part in courtship and rivalry. Teeth are acrodont. It is both herbivorous and carnivorous. Another iguanid, Amblyrhynchus, of Galapagos Islands is the only living marine lizard, though it spends much time on the shore basking in the sun and feeding on weeds.
Lizard # 5. Phrynosoma:
Phrynosoma (Fig. 24.4) is commonly known as horned toad. It grows to a length of 7.5 cm. Body is much flattened and broadened and covered with larger and smaller strongly keeled scales. Dorsal crest is absent. The underparts are covered with small very regular keeled scales. The colour of the upper part is a mixture of yellow, grey, brown and black.
Head has five spikes on each side, one post-orbital, three temporal and one occipital. The sides of the lower jaw project in the shape of prominent ridges and are protected by a series of small spines. Both the sexes have a long row of pores on the under surface of thighs.
Tongue is short and flat. Teeth are pleurodont. Vertebrae are procoelous. Viviparous. Phrynosoma is found in Western half of the United States and Central America. Phrynosoma cornutum ranges from Illinois through Kansas and Texas to Northern Mexico.
Lizard # 6. Chamaeleon:
Chamaeleon (Fig. 24.4) is an arboreal lizard of Africa, Madagascar and Europe, one species is found in South India and Sri Lanka. The scales over the body are reduced to minute tubercles. There is a row of pointed scales along the body and tail. The head and body are compressed laterally, the tail is long and prehensile. On the head is a protruding helmet formed by squamosal and occipital bones. Eyes are large with eyelids fused together leaving a pinhole in the centre.
The eyes move separately but they are focussed for binocular vision when catching an insect. The tongue is long with a swollen anterior end. The tongue is sticky and used with great precision for catching insects. Locomotion is very slow. The digits of each limb are fused together in groups of three and two digits which are used for grasping twigs.
The sensory parts of nose and organ of Jacobson are reduced. Lungs are produced into air sacs which on being inflated increase the bulk of the animal. Between the skull and atlas is a median pro-atlas.
Chamaeleon calcaratus, found in South India and Sri Lanka, is 38 cm long and has much granulated skin. Chamaeleons have a remarkable power of colour change. The dermis contains melanophores which are controlled by the autonomic nervous system and not by hormones. But chamaeleons do not assume the colours of the environment.
Lizard # 7. Varanus:
Varanus (Fig. 24.4) is commonly known as monitor. It is a primitive lizard found in Africa, Asia, and Australia and has many species. The Indian Varanus is over 60 cm long and of brownish colour with darker spots in rows. The tail is long and compressed laterally. The entire animal is covered with fine granular scales.
Neck is longer than a long flattened head. It has a long forked snake-like tongue which darts out and in, and is a sensory organ. Teeth are pleurodont. It lives in burrows and on trees. It is carnivorous. It lays eggs in a nest in the ground. An African species is 2 metre long which eats eggs and young ones of crocodiles in the Nile. Varanus komodoensis of Komodo Is. of East Indies is a 4 metre long monster weighing over 80 kg. It is a savage and carnivorous lizard.
Lizard # 8. Heloderma:
Heloderma suspectum (Fig. 24.4) is commonly called gila monster or beaded lizard. It is a stout, about 60 cm long lizard with a short and thick tail which is a reservoir of fat as in most lizards. It is covered with bead-like scales and is brownish with large black and orange patches showing warning colouration. The limbs are well developed but it moves slowly with the body hardly raised from the ground.
It is also capable of swift movements. Heloderma is the only known poisonous lizard. Modified labial glands of the lower jaw form poison glands from which a duct leads on each side into a grooved tooth. Its venom affects the nerves causing paralysis. Its eyes are fixed. It feeds on eggs of small animals. It lays eggs in a nest in sandy soil. It is found in Mexico and arid parts of Arizona.
Lizard # 9. Ophisaurus:
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Ophisaurus (Fig. 24.4) is commonly called glass snake. It is found inhabiting in bushy localities or burrowing in the sand. Body and tail are very long and snake-like but the head is that of a typical lizard.
Tail is long and very brittle. The whole body is covered with bony plates underlying the imbricate scales. The limbs are, however, reduced to a pair of small cloacal spikes, partly concealed at the sides of the cloacal opening. Due to the reduced limbs it is also known as “limbless lizard”. Eyes with movable eyelids. Ear opening is also present.
Tongue composed of two distinct portions, of which the anterior is thin emarginate, extensile and retractile into the posterior thicker portion. Teeth are pleurodont and solid. Pectoral and pelvic girdles are present. Vertebrae are procoelous.
Presence of longitudinal fold of skin on the lateral sides of the body. Oviparous. Carnivorous, feed chiefly on snails, insects, worms, mice and small lizards. Ophisaurm is found in North America, South Russia, Asia Minor and Morocco. Ophisaurus gracilis is found in the Eastern Himalayas and Myanmar.