Classes of Reptilia

• Reptiles are considered a separate class of animal because they share the characteristics of scaly skin, air breathing, egg laying and cold-bloodedness. The class of Reptilia, or reptiles, is divided into four "orders" of reptilian animals. What creatures should be included in the class is debated among scientists; modern birds descended from a reptilian ancestor, but in the prevailing system of classification are considered their own class. As more is discovered about the natural world, other rearrangements in the classification system are made. For example, snakes used to be divided into several different orders of reptiles but are now classified within the same order.

Crocodilia

• The order of crocodilia includes crocodiles, alligators and other species less familiar to Americans, such as gharials, which are found in India. There are currently 23 species of animals within this group. All crocodilians are similar in their body shape. crocodilians have heads that are held horizontally in front of their bodies and four legs that stick out from their sides. Crocodilians are also known for their heavy armor of scales and their heavy tails, and have advanced hearing, smell and sight. Crocodilians walk in a way that is different from other reptiles and is more like the gait of mammals. Also like mammals and birds, crocodilians have a a four-chambered heart. Crocodilians are found in tropical climates in North America, South America, Africa, Australia and Asia. Members of the crocodilian order live mostly in water but lay their eggs on dry land.

Sphendontia

• The Tuatara of New Zealand is the only living creature within the sphendontia order of reptiles. This order used to be very diverse, dating back 100 million years, but all other animals in this group are now extinct. The Tuatara looks like an iguana lizard because of the spikes on the head and neck and the thick tail. Tuataras live within seabird colonies in New Zealand. These animals are nocturnal predators, hunting for arthropods, small lizards, amphibians and baby seabirds. Tuataras have a long life span compared to other similar reptiles. Most Tuataras live 50 to 80 years, which is a very long life for a reptile. The Tuatara has been listed as endangered for over 100 years. It is currently described as being in a vulnerable state.

Squamata

• The order of squamata includes all Earth's lizards and snakes. This is the largest order of reptiles, with nearly 8,000 species. These animals live in all parts of the world except very cold places. Most animals within this group are not able to hear very well and smell with an organ on the roofs of their mouths. Squamata are divided into two suborders. The lacertilia suborder consists of lizards. They are distinguished by their ability to regrow parts of their tails and their eyelids. Chameleons, iguanas, and geckoes are part of the Lacertilia suborder. The serpentes suborder consists of snakes. Snakes are distinguished by their lack of eyelids and their deafness. They make up for this with sensitivity to vibrations, which helps them hunt for their prey. Cobras, constrictors, and pythons are of the order of serpentes.

Testudines

• The order of testudines includes all turtles and tortoises, encompassing about 300 species in all. This group dates back to the Triassic period, about 250 to 200 million years ago. Fossils suggest that the turtles from the Triassic period are very similar to the turtles of today. The shell of testudines distinguishes them from all other animals. This shell is a modified ribcage and cannot be taken off. Turtles are classified within the order as having either a side neck or a hidden neck. Turtles with a side neck can pull their head in sideways into the shell. Turtles with a hidden neck can draw their head straight back into their shell.