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Overlying the boney elements are a series of scutes, which are made of keratin and are a lot like horn or nail tissue. In the center of the carapace are five vertebral scutes and out from these are four pairs of costal scutes. Around the edge of the shell are 12 pairs of marginal scutes.
Dermal scutes are also found in the feet of birds and tails of some mammals, and are believed to be the primitive form of dermal armour in reptiles. The term is also used to describe the heavy armour of the armadillo and the extinct Glyptodon , and is occasionally used as an alternative to scales in describing snakes or certain fishes, such as ...
The "central scutes" extend over the dorsal mid line of the carapace from head to tail, with the "costal scutes" running along each side of the central scutes. The "marginal scutes" run along the outer sides of the shell, and the "nuchal scutes" are found in the area directly behind the turtle's head.
Typically, 11 or 12 pairs of marginal scutes rim the carapace. [8] Five vertebral scutes run down the carapace's midline, while five pairs of costal scutes border them. [21] The nuchal scute is located at the base of the head. [21] The carapace connects to the plastron by three pairs of inframarginal scutes forming the bridge of the shell. [21]
The scales and scutes of birds were thought to be homologous to those of reptiles, [4] but are now agreed to have evolved independently, being degenerate feathers. [ 5 ] [ 6 ] Carcharodontosaurid theropod dinosaur Concavenator , is known to have possessed these feather-derived tarsal scutes.
Snake scales may be modified to form fringes, as in the case of the eyelash bush viper, Atheris ceratophora, or rattles as in the case of the rattlesnakes of North America. [ 8 ] Certain primitive snakes such as boas , pythons and certain advanced snakes such as vipers have small scales arranged irregularly on the head.
The wood turtle usually grows to between 14 and 20 centimeters (5.5 and 7.9 in) in straight carapace length, [10] but may reach a maximum of 23.4 centimeters (9.2 in). [ 6 ] [ 8 ] It has a rough carapace that is a tan, grayish brown or brown in color, with a central ridge (called a keel) made up of a pyramidal pattern of ridges and grooves. [ 10 ]
The dorsal tergum, ventral sternum, and the lateral pleura form the hardened plates or sclerites of a typical body segment. In either case, in contrast to the carapace of a tortoise or the cranium of a vertebrate, the exoskeleton has little ability to grow or change its form once it has matured. Except in special cases, whenever the animal ...