Anatomical and histological analysis of an undescribed cervical skin fold structure in spotted turtles (Clemmys gutatta)

Turtles evolved over 230 million years ago during the Triassic period, and are a group of ectothermic reptiles that can be found everywhere in the world except Antarctica. There are approximately 350 species of extant turtles with a wide variety of anatomic and physiologic differences, ranging from sea turtles with large and slender flippers adapted for propulsion during swimming, to snapping turtles that have extremely flexible necks for quickly catching prey. In this study, we provide the first description of an anatomical structure arising from the cervical (neck) skin of spotted turtles (Clemmys gutatta). Based on other species evaluated in this study, the structure appears to be unique to spotted turtles. While the function is currently unknown, it is suspected to serve a protective role for the head and neck of the turtle much like the hinged shell of some other chelonians. This structure may provide clues to the evolution between a turtle that has an unhinged shell such as a yellow-bellied slider (Trachemys scripta) and a turtle that has a hinged shell such as an eastern box turtle (Terrapene carolina carolina), utilized for evading predation or danger. By describing this structure, both grossly and microscopically, we can make inferences about its possible function. The proposed name for this structure is the clemmysian fold.