What are reptiles?
Reptiles form a Class of Vertebrates (other Classes include fish,
amphibians, birds and mammals) with over 6,600 species worldwide.
Reptiles can be distinguished from other animals because of their
scaly skin and, except for snakes, true claws. There are a few
other characteristics which all living reptiles share:
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
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
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 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
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.