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.
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.
Limbs may or may not be present. If they have limbs, they are two pairs of pentadactyl limbs, each bearing claws. Snakes do not have limbs.
The heart is 3 chambered. However, crocodiles have a 4-chambered heart.
The nervous system comprises 12 pairs of cranial nerves.
Reptiles do not have external ear openings. Tympanum represents ear
They possess a typical cloaca.
Reptiles are generally uricotelic. They mostly excrete nitrogenous wastes as uric acid.
Fertilisation is internal.
They are oviparous and the eggs are very yolky. Development is direct.
E.g., Snakes, Turtles, Lizards, Crocodiles.
Classification of Reptilia
The class Reptilia is differentiated into three major sub-classes:
Anapsida
Parapsida
Diapsida
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.
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.
Diapsida
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., Crocodilus, Chameleon
Groups of Reptiles
The class Reptilia is further divided into different groups known as orders:
Order | Examples |
Order Squamata | Lizards, Snakes |
Order Testudines | Turtles, Tortoises, Terrapins |
Order Crocodilia | Crocodiles, Alligators |
Order Sphenodontia | Tuataras |
Extinct groups of class Reptilia
Ichthyopterygia
Lepidosauria
Archosauria
Synapsida
Ichthyopterygia
This group had one temporal fossa place high up on the skull.
The two largest groups belonging to this sub-class are Ichthyosaurs and Plesiosaurs.
Eg., Ichthyosaurus
Lepidosauria
These were all the lizard-like reptiles.
They had two temporal vacuities in the skull.
Eg., Youngina,
Archosauria
The skulls were diapsid.
Some were bipedal which gave rise to birds.
They also gave rise to dinosaurs.
Eg., Brontosaurus
Synapsida
They had one temporal fossa on the lower side of the skull.
These were the most dominant group of reptiles during the Permian period.
The surviving Lepidosaurs in the Mesozoic era gave rise to mammals. The rest were replaced by dinosaurs.
Eg., Plesiosaurus.
&
Win
0 Comments