A
scute or
scutum (
Latin scutum, plural
scuta "
shield") is a bony external plate or scale, as on the shell of a
turtle, the skin of
crocodilians, or the feet of some
birds.
Scutes are similar to scales and serve the same function. Unlike the scales of fish and snakes, which are formed from the epidermis, scutes are formed in the lower vascular layer of the skin and the epidermal element is only the top surface. Forming in the living dermis, the scutes produce a horny outer layer, that is superficially similar to that of scales. Scutes will usually not overlap as snake scales (but see the pangolin). The outer keratin layer is shed piecemeal, and not in one continuous layer of skin as seen in snakes or lizards. The dermal base may contain bone and produce dermal armour. Scutes with a bony base are properly called osteoderms. 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 sturgeons.
The turtles carapace is a massive scute structure, formed by a series of distinct scutes with a bony base that have grown together to form the shell. The individual scutes are termed nuchal scute, neural or vertebral or central scutes, marginal scutes, and pygal or supracaudal scute. Those in the plastron are the epiplastron, entoplastron, hyoplastron, and hypoplastron. The horny surface of the scutes are shed individually, usually over a few days.
