What Makes Turtles Different from Other Reptiles?
Turtles are indeed reptiles and highly successful ones at that. Turtles are categorized under the class Reptilia, and are further classified under the order Testuidines, which includes turtles and tortoises. Although turtles and other reptiles share many features, some characteristics of the Testudines set them apart.
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Feeding
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The head of a turtle has a long flexible neck that allows the turtle to withdraw the head into its shell for protection from predators. Unlike most other reptiles, turtles have a sharp beak that they use to eat. They do not have teeth. The beak is lined with sharp ridges and they cannot stick out their tongue out to catch prey.
Epidermis
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The epidermis of most turtles contain modified cells that form hard scutes, or scales made of keratin. These scutes compose the shell of the turtle. This tough protein keratin, is the same protein found in the turtle's beak as well as human skin and nails. The upper half of the turtle's shell is called the carapace and the lower half is called the plastron. These two halves are joined by bridges. Other reptiles have an epidermal layer of scales, but they do not modify to form a shell.
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Respiration
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Turtles have lungs as other reptiles do. However, the shell of the turtle prevents them from fully expanding the chest cavity. Turtles have thus adapted other methods of respiration. Buccal pumping pulls air into the mouth and then into the lungs using the pharyngeal muscles on the floor of the throat. Another method used by some turtles is to expand the internal volume of the shell using muscles covering the carapace. This draws air into the lungs comparatively in the same manner as a diaphragm would. Under water, turtles rely on water pressure for exhalation and muscular activity for inhalation.
Skull
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Turtles are also different from other reptiles in skeletal features. Turtles are considered anapsids, meaning the skull does not have temporal openings (called the lateral temporal fenestrae). All other living reptiles are diapsids, with two pairs of temporal openings.
Misconceptions
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Turtles are reptiles--not amphibians. Reptiles have a body covering of horny epidermal scales. They have paired limbs, usually with five toes, ribs with a sternun, respiration by lungs and a three-chambered heart (crocodilians have a four-chambered heart). All reptiles are ectothermic or "cold-blooded," meaning they must regulate their body temperature by exchanging heat with their surroundings. Reptiles have separate sexes, and direct development of offspring in which the young look like miniature versions of the adults and there is no larval stage.
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- Photo Credit turtles image by Vladislav Gajic from Fotolia.com
