Carapace Scute Variations of the Olive Ridley Sea Turtle (Lepidochelys olivacea): Polymerization as an Evolutionary Trend

The carapace scute pattern is an important morphological feature of turtles that, along with the phylogenetic stability, has a high level of intraspecific variability. The olive ridley sea turtle (Lepidochelys olivacea; Cheloniidae) demonstrates extreme instability of pholidosis, and the aim of our study is to identify the range of the carapace scute variations in this species. We studied 655 L. olivacea hatchlings from nine natural clutches on the Southern coast of Sri Lanka and identified 120 different patterns of carapace scutes. The vertebral and pleural scutes were the most variable, ranging in number from four or five to ten. Five pairs of pleural scutes, a normal condition for some species of sea turtles, were found in only 11.9% of individuals. The hatchlings with six and seven scutes in the vertebral and pleural series were the most numerous. 13 pairs of marginal scutes were the stable norm in 92.7% of individuals. Newborn turtles with symmetrical scute patterns predominated (60.9%). Comparison of the pholidosis variability in hatchlings from different clutches revealed the presence of specific scute patterns. We assume that the clutch differences are more related to the genetic characteristics of the breeding turtles than to the influence of environmental factors. The unique variable pholidosis of L. olivacea demonstrates a trend toward scute polymerization, a rare phenomenon in turtle evolution.