Soft Plastra of Adult Male Sea Turtles: An Apparent Secondary Sexual Characteristic

Wibbels, Thane; Owens, David; Rostal, David

In contrast to many turtle species, chelonid sea turtles do not exhibit sexual size dimorphism (Carr 1952; Pritchard 1979). However, chelonid sea turtles do have several sexual dimorphisms (Carr 1952; Pritchard 1979) that appear to facilitate successful mating. Adult males have long prehensile tails with a heavy terminal nail in contrast to adult females whose tails barely reach the rear margin of the carapace. The claws on the front flippers of adult males are longer and more strongly curved than those of adult females. Additionally, the posterior portion of the carapace of adult females is commonly more rounded than that of adult males. Collectively, these morphological characteristics enhance a male's ability to successfully mount a female. These secondary sexual characteristics also provide a means by which investigators can sex adult chelonid turtles and thus, are of importance to population studies. We have observed what we suspect is an additional secondary sexual characteristic in chelonid sea turtles. Figure 1 a shows the plastron of an adult male loggerhead, Caretta caretta, captured in the Cape Canaveral ship channel during April of 1983. The scutes on the medial portion of the plastron are relatively soft, lacking the hard cornified layer and exposing relatively soft and leathery epidermal tissue. These soft areas do not appear to be skin separating the scutes, such as that seen in musk turtles, Sternotherus spp. Rather, these areas appear to be scutes which lack a cornified surface.

Soft Plastra of Adult Male Sea Turtles: An Apparent Secondary Sexual Characteristic

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