There are over 6300 species belonging to the class Amphibia including frogs, toads, salamanders, newts and caecilians. Amphibians are cold-blooded (poikilothermic) animals whose skin is covered in a layer of mucus which helps to keep them moist. Most amphibians lay eggs in water and then go through metamorphosis from a juvenile water-breathing form, to an adult air-breathing form. Amphibians typically have four limbs, however, caecilians are legless.
Members of the Class Reptilia are characterized as air-breathing, egg-laying, cold-blooded (poikilothermic) animals whose skin is usually covered by scales. Comprised of more than 8200 species, the classification of reptiles is often the topic of debate among many modern taxonomists. Most scientists agree that the class Reptilia consists of four orders; Crocodilia (crocodiles and alligators), Spenodontia (tuataras), Squamata (snakes and lizards), and Testudines (turtles). However, some taxonomists believe these four orders should be re-classified and divided into distinct Classes. There is good evidence to support this separation but the debate continues.
Snakes and Lizards
All snakes and lizards belong to the Order Squamata. This large Order consists of approximately 6700 known species and are found on all continents except Antarctica. The squamates are a diverse group, ranging in size from the tiny dwarf gecko, measuring less than an inch in length, to the enormous 26 ft. anaconda. Most lizards possess limbs and external ears, these characteristics are not found in snakes.
The common name “turtle” refers to any member of the order Testudines. Turtles are generally characterized by their protective, bony shell, formed from a modified rib cage. The earliest known turtles date from 215 million years ago. Today, there are approximately 300 species of turtles, many of which are now endangered.
Crocodiles, Alligators & Gavials
There are 23 species of crocodilians found around the world. The smallest crocodilian species is the Cuvier’s Dwarf Caiman, rarely growing over 5 feet in length. The largest crocodilian is the Saltwater Crocodile, capable of growing to lengths of 18 to 20 feet. Crocodilians first appeared about 84 million years ago in the late Cretaceous Period and are the closest living relatives of modern birds.