Reptilia General Characteristics, Classification and Examples | Free Biology Notes

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Reptilia General Characteristics

• They are basically terrestrial but some are aquatic
• Body is divided into 4 parts:- Head, neck, trunk and tail
• They are cold blooded animals or poikilotherm
• Limbs two pairs, five clawed digits in each limb (Some limbless)
• Skin dry, rough and non glandular. Endoskeleton is made up of epidermal scales or plates
• Alimentary canal terminates into cloaca
• Respiration only by lungs
• Heart is usually 3 chambered or partially four chambered (4 Chambered in crocodile)
• Brain developed, cranial nerves 12 pairs
• Ear in the form of tympanum
• Jacobson’s organ present in the roof of buccal cavity concerned with smell
• They are unisexual, oviparous, internal fertilisation.
• Development is direct. No metamorphosis and parental care found

Classification of Reptilia

The class Reptilia is differentiated into two major sub-classes: Anapsida and Diapsida

Subclass 1. 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.
• These are include only one order – Chelonia

Order – Chelonia

• Terrestrial, marine and fresh water animals
• Body covered in two shell plates:- Dorsal shell – carapace and Ventral shell – Plastron
• Limbs clawed, webbed and paddle like
• Jaws horny beak like and no teeth
• All three organs can be withdrawn in carapace
• Cloacal aperture helps in respiration (Cloacal respiration)
• E.g., Che lone (turtle), Testudo (Tortoise), Trionyx (Terrapin)

Subclass 2. 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 three orders – Rhynchocephalia, Squamata and Crocodilia

Order 1. Rhynchocephalia

• Most of the species of this order are found in form of fossils
• Only sphenodon punctatum species is live (found in new Zealand only)

Order 2. Squamata

Squamata It includes two suborders:- Lacertilia and Ophidia

Suborder (1) Lacertilia

• Limbs will developed
• Eyelids movable
• Nictitating membrane found in eye
• Tympanum present
• E.g., Lizards, such as Chameleon (Tree lizard), Calotes (Garden lizard), Hemidactylus (wall lizard)

Suborder (2) Ophidia

• Limbs are absent
• Eye lids immovable
• Nictitating membrane absent
• Tympanum absent
• E.g., snakes, such as Naja (Cobra), Bungarus (Krait), Vipera (Viper).

Order 3. Crocodilia

• Freshwater animals found on land and water
• 4 chambered heart present
• Largest modern reptiles
• Skin is covered by bony plates
• Snout long
• E. g., Crocodilus (Crocodile), Alligator, Gavialis (“Gharial”).

Extinct Groups of Class Reptilia:

Following extinct groups of class reptilia are important to mention here.

i. Cotylosauria:
They were most primitive reptiles and closest to early amphibians. They were without temporal fossae in the skull, e.g., Seymouria.

ii. Ichthyopterygia:
They were fish-like and had single fossa in the skull e.g. Ichthyosaurus. ’

iii. Archosauria:
They had diapsid skulls. Some were bipedal and gave rise to birds. A group of Archosauria also gave rise to dinosaurs, e.g., Brontosaurus.

iv. Synaptosauria:
The skull had a single temporal fossa on either side. They were mammal-like reptiles that later on gave rise to mammals, e.g. Plesiosaurus.