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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.
Scutes on an alligator foot A scute ( / s k j uː t / ⓘ ) or scutum ( Latin : scutum ; plural: scuta " shield ") is a bony external plate or scale overlaid with horn, as on the shell of a turtle , the skin of crocodilians , and the feet of birds .
Typically, a turtle has 38 scutes on the carapace and 16 on the plastron, giving them 54 in total. Carapace scutes are divided into "marginals" around the margin and "vertebrals" over the vertebral column, though the scute that overlays the neck is called the "cervical". "Pleurals" are present between the marginals and vertebrals. [20]
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]
Squamata and Rhynchocephalia form the subclass Lepidosauria, which is the sister group to the Archosauria, the clade that contains crocodiles and birds, and their extinct relatives. Fossils of rhynchocephalians first appear in the Early Triassic , meaning that the lineage leading to squamates must have also existed at the time.
[8] [9] The outer shell is composed of ossified dermal scutes covered by nonoverlapping, keratinized epidermal scales, which are connected by flexible bands of skin. This armor covers the back, sides, head, tail, and outside surfaces of the legs.
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 adult's oval carapace is almost as wide as it is long and is usually olive-gray in color. The carapace has five pairs of costal scutes. In each bridge adjoining the plastron to the carapace are four inframarginal scutes, each of which is perforated by a pore. The head has two pairs of prefrontal scales. These turtles change color as they ...