|Reptiles (traditional classification)|
Order Crocodilia (Crocodilians)|
Order Rhynchocephalia (Tuataras)
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
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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http://tolweb.org/tree?group=Synapsida&contgroup=Amniota see also: