EVOLUTION OF LIZARDS AND SNAKES
Lizards arose from early reptiles about 200 million
years ago and are found on all the continents except Antarctica.
There are about 3,750 species of lizards, making them one of the
largest and most successful groups of reptiles. None of Australiaís
500 species are venomous.
LIZARDS AND SNAKES
Both snakes and lizards are classified in the same order, Squamata,
but lizards are separated into their own suborder, Sauria. Lizards
generally can be distinguished from snakes by the presence of two
pairs of legs suited for rapid locomotion, external ear openings
flush with the skin and moveable eyelids. But these convenient
external diagnostic features, while absent in snakes, are also absent
in some lizards. Lizards can be precisely separated from snakes,
however, on the basis of certain internal characteristics. All
lizards have at least a vestige of a pectoral girdle (skeletal supports
for the front limbs) and sternum (breastbone). The lizard's
ribs are never forked, as are one or two pairs in a snake. The
lizard's brain is not totally enclosed in a bony case but has a
small region at the front covered only by a membranous septum. The
lizard's kidneys are positioned symmetrically and to the rear.
What makes a Lizard a LIZARD sub-order Lacertilia,
and not a SNAKE sub-order Ophidia?
1. Most lizards have short bodies and
four limbs, snakes never have front limbs.
2. The two
halves of the lower jaw are united, unlike a snakes which are joined
3. Lizards have a flat fleshy tongue, except
for goannas which have a snake like forked tongue.
lizards have an external ear opening, snakes donít have any sign
of an external ear.
5. Many lizards have movable eyelids,
snakes do not.
Lizards belong to the scientific sub-order
Lacertilia, a division of the reptile class Reptilia.
Lacertilia is divided up into different families.
lizards belong to the following five families: -
are usually small velvety lizards up to 10 cm long which live under
bark, logs, rocks or in burrows or litter. Their main characteristics
are bulging eyes with oval shaped vertical pupils for night vision,
teeth on the side of the bone that supports them, skin without overlapping
scales and tails which they can shed.
are the largest group of lizards in Australia. Their skin is usually
smooth and shiny. Most have 5 toes on each of their four legs, as
do other lizards. Most Skinks are ground dwellers, have immovable
eyelids and can shed their tail.
are powerfully built with strong limbs, a pointed wedge-shaped head
and a long muscular tail. The shin of goannas is tough and
leathery and the scales do not overlap. Their teeth are long and
backward-curving in order to grab their prey securely.
have dull rough scales which lie side by side and well suited to
desert conditions. As with goannas, they are unable to regenerate
the tail once it is broken. The eyes are small with prominent eyelids,
while the tongue is broad and short.
Lizards have rudimentary limbs if any and a fleshy tongue. They
are long and thin and burrow under soft earth and debris. Being
of plain colours and nocturnal Legless Lizards are rarely seen.
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