Diversity of reptiles

Reptiles range in body form from crocodilians to squa-mates, tuatara, and turtles. This diversity borders on trivial, however, in comparison with the range of forms and lifestyles that existed during the Jurassic and Cretaceous periods. This point can be further appreciated by considering locomotion

Parson's chameleon (Calumma parsonii parsonii) has a prehensile tail as long as its body length that can be used for climbing, grasping, or perching. At rest or during sleep the tail is coiled, as shown here. The specialized feet are divided into two bundles of fused toes, consisting of three on the outside and two on the inside of the rear feet. This is reversed on the front feet, giving them the ability to grasp, perch, and climb, and facilitates their largely arboreal existence. They are also able to use their highly dextrous feet to remove shed skin and put food into or take objects out of their mouths. (Photo by Ardith Abate. Reproduced by permission.)

Parson's chameleon (Calumma parsonii parsonii) has a prehensile tail as long as its body length that can be used for climbing, grasping, or perching. At rest or during sleep the tail is coiled, as shown here. The specialized feet are divided into two bundles of fused toes, consisting of three on the outside and two on the inside of the rear feet. This is reversed on the front feet, giving them the ability to grasp, perch, and climb, and facilitates their largely arboreal existence. They are also able to use their highly dextrous feet to remove shed skin and put food into or take objects out of their mouths. (Photo by Ardith Abate. Reproduced by permission.)

among lizards with well-developed legs. Although some species are capable of quick movement, the gait of all lizards is basically the same as that of salamanders. The legs extend from the sides and must support the body through right angles, greatly limiting body mass and speed. Within the context of these constraints, lizards do quite well, but their locomotion remains relatively primitive. Truly advanced locomotion, with the legs directly under the body, occurs among mammals, but this pattern of limb suspension evolved in dinosaurs and was clearly a part of their long period of success. All extant reptiles are ectotherms, deriving their body heat from radiation, conduction, or convection, whereas mammals and birds are endotherms, producing body heat by energy-consuming metabolic activity. Thus we see the primitive condition in the reptiles and the advanced condition in the birds and mammals. There is now good reason to believe that at least some dinosaurs were endotherms. Accordingly, it is important to keep in mind that the diversity of extant reptiles is but a fraction of the diversity exhibited by this class of vertebrates during earlier phases of its natural history.

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