Scutes are the individual plates forming the outer layer of a turtle’s shell. Made of keratin, similar to human fingernails, scutes serve as a protective covering. They overlay the bony shell plates, adding defense against predators and impacts. This arrangement enhances the shell’s strength.
Understanding Turtle Scutes
A turtle’s shell consists of two primary parts: the domed upper section known as the carapace and the flatter underside called the plastron. Each of these sections is covered by a distinct set of scutes, arranged in specific patterns. The scutes themselves do not directly correspond to the underlying bone structure, creating staggered seams that enhance the shell’s integrity.
The carapace features scutes arranged in a consistent pattern, including five vertebral scutes along the midline and four pairs of costal scutes flanking them. Encircling the rim are 12 pairs of marginal scutes, forming a border. A single nuchal scute is often at the front edge, behind the neck, and some species may have a supracaudal scute at the very rear.
The plastron, or belly shell, is covered by a symmetrical arrangement of 12 scutes. These are present in six pairs, named for their location on the underside: gular, humeral, pectoral, abdominal, femoral, and anal scutes. These plastral scutes protect the turtle’s soft underbelly and internal organs. The seams between these scutes can sometimes estimate a turtle’s age, as new growth rings may form annually.
Factors Influencing Scute Number
While a common pattern of scute arrangement exists, the exact number can vary among different turtle species. For instance, some sea turtle species like the Kemp’s ridley have five pairs of costal scutes instead of four. Other species might exhibit variations in the number of marginal scutes or the presence of an additional intergular scute on the plastron, common in pleurodiran turtles. These species-specific differences are often used for identification.
Deviations from the typical scute count, known as anomalies, can occur within a species. These include supernumerary scutes (extra scutes) or fused scutes (where two or more merge). Such variations are often linked to genetic factors, influencing scute pattern development.
Environmental influences during embryonic development can contribute to scute anomalies. Factors such as incubation temperature and humidity can impact scute formation, leading to variations in their number or arrangement. For example, high incubation temperatures have been observed to increase the frequency of supernumerary scutes in some species. While some anomalies might not significantly affect a turtle’s survival, they highlight the interplay between genetics and environment in shaping these protective structures.