12.18: Reptile Classification

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With so many possible colors, how would a chameleon be classified?

Chameleons are a distinctive and highly specialized type of lizard. They are distinguished partly by their parrot-like feet, their separately mobile and stereoscopic eyes, their very long, highly modified, and rapidly extrudable tongues, crests or horns on their distinctively shaped heads, and the ability of some to change color. But there are approximately 160 species of chameleons. So how are they classified?

Classification of Reptiles

There are more than 8,200 living species of reptiles, with the majority being snakes or lizards. They are commonly placed in four different orders. The four orders are described in Table below.

Order	Characteristics	Example
Crocodilia: crocodiles, alligators, caimans, gharials	They have four sprawling legs that can be used to gallop; they replace their teeth throughout life; they have strong jaws and a powerful bite; they have a more advanced brain and greater intelligence than other reptiles; they have a four-chambered heart.	caiman
Sphenodontia: tuataras	They are the least specialized of all living reptiles; their brain is very similar to the amphibian brain; they have a three-chambered heart, but it is more primitive than the heart of other reptiles.	tuatara
Squamata: lizards, snakes	Lizards: most have four legs for running or climbing, and they can also swim; many change color when threatened; they have a three-chamberedheart. Snakes: they do not have legs, although they evolved from a tetrapod ancestor; they have a very flexible jaw for swallowing large prey whole; some inject poison into their prey through fangs; they have a three-chambered heart.	lizard
Testudines:turtles, tortoises, terrapins	They have four legs for walking; they have a hard shell covering most of their body; they have a three-chambered heart.	terrapin

Summary

There are more than 8,200 living species of reptiles, and they are placed in four orders: Crocodilia, which includes crocodiles and alligators; Sphenodontia, or tuataras; Squamata, which includes lizards and snakes; and Testudines, such as turtles and tortoises.

Review

Compare and contrast crocodilians with other orders of reptiles.