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These scales, which on the surface are composed of horny (keratinized) epidermis, may have bony plates underlying them; these plates are called osteoderms. Lizard scales may differ strongly in form on different parts of the lizard and are often of use in taxonomy to differentiate species (or higher taxa, such as families).
Most snakes have extra broad scales on the belly, each scale covering the belly from side to side. The scales of all reptiles have an epidermal component (what one sees on the surface), but many reptiles, such as crocodilians and turtles, have osteoderms underlying the epidermal scale.
The ocular scale proper is a transparent scale covering the eye which is called the spectacle, brille or eyecap. [9] [23] The circumorbital scales towards the snout or the front are called preocular scales, those towards the rear are called postocular scales, and those towards the upper or dorsal side are called supraocular scales.
Reptiles, including snakes, possess extensive keratinization of the epidermis in the form of epidermal scales. [10] A snake's epidermis is composed of four layers. The outer layer of a snake's skin is shed periodically, and is therefore a temporary layer, and is highly keratinized.
Exposed parts of reptiles are protected by scales or scutes, sometimes with a bony base , forming armor. In lepidosaurs, such as lizards and snakes, the whole skin is covered in overlapping epidermal scales. Such scales were once thought to be typical of the class Reptilia as a whole, but are now known to occur only in lepidosaurs.
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 [citation needed]. Forming in the living dermis, the scutes produce a horny outer layer that is
Dating from around 289 million years ago, it is the oldest known sample of a preserved epidermis, which is the outside layer of skin on terrestrial reptiles, birds and mammals. The epidermis ...
The ratio of scale size to osteoderm size and their organization vary by species. [7] The majority of species have a one to one ratio of scales to osteoderms, with little correlation between the layout. [3] In the girdle-tailed lizards, for example, the scales and osteoderms are of the same size and shape and are organized alongside each other.