The early ontogeny of carapace armoring in hawksbill sea turtles ( Eretmochelys imbricata ), with comparisons to its close relatives (Loggerhead, Caretta caretta ; Kemp's ridley, Lepidochelys kempii )

In this study, we compare and contrast armoring strategies during early ontogeny among three related species of marine turtles: the hawksbill, a species that diverged about 29 mya from the loggerhead and Kemp's ridley, which diverged from one another about 16 mya. Our purpose was to determine whether there was a correlation between divergence time and the evolution of unique morphological armoring specializations among these species. To find out, we completed a more detailed analysis of shell morphology for all of the species that revealed the following patterns. First, each species has evolved a somewhat different armoring strategy, suggesting that shell morphological evolution is surprisingly flexible. Second, hawksbills possess armoring features that are unique among all marine turtle species, suggesting a correlation between divergence through time and divergence in morphology. However, hawksbills also frequent coral reefs and selection pressures promoting their survival in those habitats may also have shaped their unique morphology. In contrast, loggerhead and Kemp's ridley turtles share similar armoring features that differ primarily in when during ontogeny they appear and in their degree of expression. Third, the armoring adaptations shown generally by juvenile marine turtles resemble those found among marine fishes of comparable size, probably because both small turtles and fishes are exposed to similar predators that promote evolutionarily similar adaptations.