Reptiles are air-breathing vertebrates that first adapted to life on land. They are classified as belonging to the class Reptilia, which includes over 10,000 species ranging from snakes and lizards to crocodiles and turtles. Reptiles are divided into three main groups based on skull structure: anapsids having a single opening; parapsids having one opening; and diapsids having two openings. Diapsids are the most diverse and include dinosaurs, pterosaurs, as well as orders like squamates, crocodilians, turtles, and the sole living tuatara species.

1. CLASS - REPTILIA
Dr. G. D. HANDE

2. Reptilia
These were the first class of organisms to adapt to life on land.
They are believed to have evolved from the amphibians
millions of years ago.
There are about 10000 different species of reptiles on earth.
They are cold-blooded animals belonging to the phylum
Chordata of Animal kingdom.
The skull of the reptiles is modified that gives the reptiles an
efficient and powerful jaw action. The modification also
makes the skull light.

3. Reptiles are air-breathing vertebrates covered
in special skin made up of scales, bony plates,
or a combination of both. They include crocodiles,
snakes, lizards, turtles, and tortoises.
Today, animals belonging to class reptilian range in size
from tiny geckos to huge saltwater crocodiles that
measure more than 19 feet in length.
There are approximately 10,700 extant reptile species.

4. Characteristics of Reptilia
Following are the important characteristics of the animals
belonging to Class Reptilia:
These are creeping and burrowing terrestrial animals with scales
on their body.
They are cold-blooded animals found in most of the warmer
regions of the world.
Their skin is dry, and rough, without any glands.
The body is divided into head, neck, trunk, and tail.
Few of these shed the scales on their skin as skin cast.
The respiration takes place with the help of the lungs.
The skull is monocondylic.

5. They have two pairs of pentadactyl limbs, each bearing
claws. Snakes are an exception.
The heart is 3 chambered. However, crocodiles have a 4-
chambered heart.
The nervous system comprises of 12 pairs of cranial nerves.
The lateral line system is absent in reptiles.
 Except for snakes, all the reptiles have well-developed ears.
 They possess a typical cloaca.
 Reptiles are ureotelic, uricotelic, and ammonotelic.
Fertilization is internal.
They exhibit a meroblastic segmentation.
They are oviparous and the eggs are very yolky.
Eg., Snakes, Turtles, Lizards, Crocodiles

6. Classification of Reptilia
The class Reptilia is differentiated into following major
sub-classes:
 Anapsida
Parapsida
Diapsida
The reptile groups also show a diversity of morphologies.
Some groups, such as most lizards and all crocodiles, possess
strongly developed limbs, whereas other groups, such as the
worm lizards and snakes, are limbless.
Reptilian body flexibility ranges from the highly flexible
forms found in snakes to the inflexible bodies of turtles. In
addition, the tails of most turtles tend to be short, especially
when compared with the long heavy tails of crocodiles.

8. Anapsida
The dermal bones form a complete roof over the skull
with no temporal fossae.
These are sub-divided into Cotylosauria and Chelonia.
Modern chelonians are classified according to the method
of retracting the head in the shell.
Turtles, tortoises, and terrapins belong to this group.
No temporal skull openings; body in bony shell; no teeth in
living members; oviparous.
Anapsid reptiles are characterized by a primitive skull with
no temporal openings. Turtles are the only living
representatives and belong to one order.
Thus, when we refer to chelonians, we refer to turtles,
tortoises, and terrapins as a group.

10. Parapsida
These reptiles possess one temporal fossa present high up on
the skull.
Protosaurs, Nothosaurs, Placodonts showed this type of skull.
The two largest groups among these were- Ichthyosaurs and
Plesiosaurus.
These became extinct at the end of the Cretaceous period
when several other reptiles including dinosaurs died.
A subclass of reptiles in which the skull has two dorsal
temporal openings adjoining the parietals and which includes
the ichthyosaurs and related extinct forms and sometimes the
lizards and snakes.

11. This group includes extinct forms.
Those forms lived from cretaceous period.
Their skull shows one pair of temporal vacuities.

12. Diapsida
The name Diapsida means "two arches", and diapsids
are traditionally classified based on their two ancestral
skull openings (temporal fenestrae) posteriorly above
and below the eye. This arrangement allows for the
attachment of larger, stronger jaw muscles, and
enables the jaw to open more widely.
There are two temporal vacuities in the skull.
They are diverse of all reptiles.
The dinosaurs and pterosaurs are included in this group.
These are divided into two major groups- Archosauria and
Lepidosauria.
Eg., Chameleon

13. These Reptiles skull shows two temporal vacuities.
Modification of typical diapsid condition is common among
these members.
This subclass is divided into two super orders Lëpidosauria
and Archosauria.

14. Order Examples
Order Squamata Lizards, Snakes
Order Testudines
Turtles, Tortoises,
Terrapins
Order Crocodilia Crocodiles, Alligators
Order Sphenodontia Tuataras
Groups of Reptiles
The class Reptilia is further divided into different groups
known as orders:

15. The Vertebrae procoelous and the rib articulates
with the backbone by a single head.
The lower jaw hinges upon a movable quadrate.
Order Squamata
Squamata is the largest order of reptiles, comprising
lizards, snakes, and amphisbaenians (worm lizards),
which are collectively known as squamates or scaled
reptiles.
Squamata (scaled reptiles) is the most diverse order of
extant reptiles, comprised of the lizards and snakes and
characterized a flexible jaw structure (movable quadrate
bones) and having scales or shields rather than shells or
secondary palates.

17. These reptiles are easily recognized by the presence
of a dorsal bony carapace and a ventral bony
plastron, with the limb girdles located inside the ribs.
All living forms lack teeth, have internal fertilization,
and lay shelled amniotic eggs.
Order Testudines
Tortoises have more rounded and domed shells where
turtles have thinner, more water-dynamic shells.
One major key difference is that tortoises spend most
of their time on land and turtles are adapted for life
spent in water. Tortoises have club-like forelegs and
'elephantine' hind legs.

18. Order Crocodilia
Crocodile, (order Crocodylia, or Crocodilia), any of
23 species of generally large, ponderous, amphibious
animals of lizard-like appearance and carnivorous habit
belonging to the reptile order Crocodylia. Crocodiles
have powerful jaws with many conical teeth and short
legs with clawed webbed toes.

20. Order Sphenodontia
Sphenodontia includes only one living genus that has just
two living species, both tuataras (Sphenodon).
The tuatara is a sphenodont that is found only in New
Zealand.
The two species of tuatara are the only surviving members
of the sphenodontians, who lived around 200 million
years ago.
Their teeth are extensions of their jaw bones, rather than
individual teeth sitting in bony sockets.
They are able to hear, although no external ear or eardrum
is present, and they have a number of unique features in their
skeleton, some of which are apparently retained from fish.