what is a turtle scute

A scute is a bony external plate or scale overlaid with horn, found on the skin of some reptiles, birds, and mammals. In turtles, the entire carapace or upper shell is a structure of fused scutes. The scutes running down the center of the shell along the spine are called central scutes. The next rows of scutes on either side of the spine are called costal scutes, and the outer scutes are known as marginal scutes. The plastron or underside of the turtle’s shell is also made up of scutes. The individual scutes have specific names and are generally consistent across the various species of turtles. They are built similarly to scales and serve the same function. Unlike the scales of lizards 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 the pangolin is an exception. Each scute forms in a lower layer of the skin, the dermis, under the epidermis. It may contain bone at its base, in which case it is known as an osteoderm. The rest of the scute consists of a fibrous protein, also found in horns, known as keratin. Unlike snakes and lizards that shed their entire outer layer of skin, animals with these structures shed only the outer layer of keratin. When a turtle grows, the scutes shed or peel away, and the new scute that grows underneath is larger than the old scute. This process is similar to a snake shedding.