In this article we will discuss about:- 1. General Characteristics of Class Reptilia 2. Classifications of Living Reptiles 3. Extinct Groups 4. Embryonic Membrane 5. Features.
General Characteristics of Class Reptilia:
Some of the general characters of class Reptilia are listed below:
1. Reptiles are the creeping and burrowing cold blooded vertebrates bearing epidermal scales. They are ectothermic (cold-blooded) and are found mostly in the warmer parts of the world. They are few in colder parts. They are mostly terrestrial animals. There are about 6,000 living species of reptiles in the world.
2. Skin is dry, rough and without glands, bearing epidermal scales or scutes.
3. Snakes and lizards shed their scales as skin cast.
4. They do not respire by means of gills. Respiration always takes place through lungs. Ribs help to expand and contract the body cavity, making the lung respiration more efficient than in amphibian.
5. Skull is monocondylic, i.e., with single occipital condyle.
6. Except in snakes, there are two pairs of pentadactyl limbs, each with 5 digits bearing claws— tetrapodus pentadactyl type.
7. Heart consists of two auricles and a partially divided ventricle. In crocodilians, heart is four chambered (two auricles and two ventricles). Renal portal system is less developed. RBCs are nucleated.
8. Kidneys are metanephric. Urinary bladder may be present. Crocodiles are ammonotelic. Turtles and alligators are ureotelic. Lizards and snakes are uricotelic.
9. Twelve pairs of cranial nerves are present.
10. Each ear consists of three parts; external, middle and internal. Snakes do not possess ears.
11. The lateral line system is altogether absent.
12. Tortoises feed almost entirely on vegetation. Some turtles are flesh eaters. All other reptiles are carnivorous/insectivorous.
13. A typical cloaca is present.
14. They are mostly oviparous. Reptiles lay macrolecithal eggs (= polylecithal eggs). Some forms are ovoviviparous or viviparous. Embryonic membranes (chorion, amnion, allantois and yolk sac) are formed during development.
Classifications of Living Reptiles:
Living Reptiles are divided in to following Subclass:
Skull has a solid bony roof, no temporal vacuities. It includes only single living order chelonia e.g., Che lone (turtle), Testudo (Tortoise), Trionyx (Terrapin)—soft shelled turtle of Indian rivers. Sub class
Skull has two temporal vacuities. It includes three living orders.
Order 1. Rhynchocephalia e.g., Sphenodon (Tuatara)—a living fossil.
Order 2. Squamata It includes two suborders:
(i) Suborder Lacertilia (Sauria) e.g., Lizards, such as Chameleon (Tree lizard), Calotes (Garden lizard), Hemidactylus (wall lizard),
(ii) Suborder Ophidia e.g., snakes, such as Naja (Cobra), Bungarus (Krait), Vipera (Viper).
Order 3. Crocodilia e. g., Crocodilus (Crocodile), Alligator, Gavialis (“Gharial”). They have
(i) the codont teeth,
(ii) Lungs in pleural cavities,
(iii) a muscular diaphragm, analogous to that of mammals and
(iv) 4-chambered heart.
Extinct Groups of Class Reptilia:
Following extinct groups of class reptilia are important to mention here.
They were most primitive reptiles and closest to early amphibians. They were without temporal fossae in the skull, e.g., Seymouria.
They were fish-like and had single fossa in the skull e.g. Ichthyosaurus. ’
They had diapsid skulls. Some were bipedal and gave rise to birds. A group of Archosauria also gave rise to dinosaurs, e.g., Brontosaurus.
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.
Embryonic Membranes of Reptilia:
During development, in reptiles, birds and mammals, embryo forms four membranes called embryonic membranes. These are chorion, amnion, allantois and yolk sac. Due to their occurrence, reptiles, birds and mammals are called amniotes. Fishes and amphibians do not have these membranes, hence they are called an amniotes.
Features of Reptilia:
Four features make reptiles true land animals:
(i) Internal fertilization,
(ii) The amnion (embryonic membrane) encloses the embryo and provides it with a watery environment during development, therefore, embryo does not need watery environment
(iii) Shell around egg to check desiccation, and
(iv) Horny scales on body of reptiles check loss of water.