The teeth of reptiles are also less specialized in function than are mammalian teeth. Instead, they have upper and lower horny plates that serve to bite off chunks of food. (They are neither flat-crowned nor used to grind food.) Turtles, except for the earliest extinct species, lack teeth. Some species have conical teeth at the front of the jaws and cuspid teeth toward the rear, but the latter are not comparable to the molars of mammals in either form or function. Lizards have conical or bladelike bicuspid or tricuspid teeth. However, only one row of teeth is present on the lower jaw. Snakes and many extinct reptilian groups have teeth on the palatal bones (vomer, palatine, pterygoid) and on the bones of the upper jaw (premaxilla, maxilla).
Crocodiles among the living forms and dinosaurs among the extinct forms have but a single upper and a single lower tooth row. The principal differences between species lie in the number, length, and position of the teeth. Venomous snakes have one or several hollow or grooved fangs, but they have the same shape as most snake teeth. Instead, the entire tooth row is usually made up of long conical teeth. A dentition that divides groups of teeth into distinctive bladelike incisors, tusklike canines, and flat-crowned molars occurs in mammals but does not occur in reptiles. The dentition of most reptiles shows little specialization in a given row of teeth. An almost complete transition between these two very different arrangements is known from fossils of early synapsids (order Therapsida). In contrast, the lower jaw of a mammal is made up of a single bone, the dentary the articular and quadrate have become part of the chain of little bones in the middle ear. Behind the dentary a small bone, the articular, forms a joint with the quadrate bone near the rear of the skull. Reptiles have a number of bones in the lower jaw, only one of which, the dentary, bears teeth. The skulls of modern reptiles are also sharply set off from those of mammals in many ways, but the clearest differences occur in the lower jaw and adjacent regions. Reptiles lack an otic notch (an indentation at the rear of the skull) and several small bones at the rear of the skull roof. In addition to differences in openings on the side of the skull and in general shape and size, the most significant variations in reptilian skulls are those affecting movements within the skull.Īs a group, reptilian skulls differ from those of early amphibians. The skulls of the several subclasses and orders vary in the ways mentioned below. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.
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