Reptile Biology

What are reptiles?

They are ectotherms (often referred to as cold-blooded). This means that reptiles do not hold their body temperature constant like mammals, but their internal temperature depends upon that of the surrounding environment. The exception is some large sea turtles which have some ability to regulate their body temperature metabolically. It is believed that some dinosaurs may also have been warm-blooded.

Reptiles have complex, shelled eggs similar to a bird's, which are laid on land. In some species, especially those in cooler climates, the female retains the eggs inside (ovoviviparity) or has a primitive placenta which feeds the embryos directly (viviparity). In these cases the young are born directly rather than being laid as eggs.

Unlike bird eggs, the shells of reptile eggs are often soft and leathery. In many species the eggs are laid in moist soil. They absorb some water and may enlarge in size after being laid.

Unlike amphibians, all reptiles have internal fertilization of the eggs by the male.

How many kinds of reptiles are there?

There are four major groups or Orders of living reptiles. Two of these are found in Canada, the turtles (Testudines) and the lizards and snakes (Squamata). The crocodiles (Crocodylia) which include alligators are confined to tropical and subtropical areas. The final Order of living reptiles are the Rhynchocephalia represented by a single species, the Tuatara (Sphenodon punctatus). These are restricted to small islands off the coast of New Zealand.

There are also several groups of reptiles which are now extinct. The most famous of these are the dinosaurs. Although extinct their descendents are still with us and are among the most well known group of animals around -- the birds. Another less well known group of early reptiles, the Synapsida, gave rise to the mammals -- and you and I.