Reptile

Reptiles (traditional classification)

Scientific classification

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Orders

Order Crocodilia (Crocodilians)
Order Rhynchocephalia (Tuataras)
Order Squamata
Suborder Sauria (Lizards)
Suborder Serpentes (Snakes)
Order Testudines (Turtles and their kin)

The reptiles are a group of vertebrate animals, today represented with four orders:

Order Testudines (turtles): approximately 300 species
Order Rhynchocephalia (tuataras from New Zealand): 2 species
Order Squamata (lizards and snakes): approximately 7,600 species
Order Crocodilia (crocodilians: crocodiles and alligators): 23 species

Reptiles are found on all continents except in Antarctica, although their main distribution comprises the tropics and subtropics. Reptiles don't have a constant body temperature. They are only able to a limited extend to actively regulate their body temperature, which is largely dependent on the environmental temperature. Most reptile species are carnivorous and egg-laying. Some species are ovoviviparous, and a few species are truly viviparous.

Classification of reptiles

Reptiles include all the amniotes except birds and mammals. Traditionally, they were grouped together in the class Reptilia, as biologists had observed common features among them. However, in recent years biologists have tendended to emphasize that groups should be monophyletic, i.e. include all descendants of a particular form. Since birds originated from a particular group of reptiles, members of that group (including Crocodilia) are closer related to them than to other reptiles. Similarly certain extinct forms are closer to mammals than to any extant reptiles. As such, the Reptilia are a paraphyletic group.

Newer systems abandon or alter the composition of the Reptilia. The synapsids, comprising mammals and their close relatives, are typically excluded. If the other amniotes are all closer related to each other than to the synapsids, as is currently expected, than they form a monophyletic group, which is called the Reptilia or Sauropsida. However, it should be noted that this group includes birds.

Evolution of the reptiles

Several thousand fossil species showing a clear smooth transition from the ancestors of reptiles to present-day reptiles exist.

In addition the transition from synapsid reptiles to mammals is one of the best detailed transitions, with in many cases the lineage being traced down to the genus level, from paleothyris to climolestes. One offshoot branch is still alive today (monotremata).

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Weblinks:
http://tolweb.org/tree?group=Synapsida&contgroup=Amniota

see also:
Reptilian humanoid