Chondro-osseous morphology of Dermochelys coriacea, a marine reptile with mammalian skeletal features

The marine leatherback turtle, Dermochelys coriacea (Testudines, Dermochelyidae), is the largest known extant reptile, reaching weights >680 kg. It has a cosmopolitan oceanic distribution, nesting in tropical climates but migrating widely into colder temperate and boreal waters1. Recent studies have shown that the leatherback has certain well developed thermoregulatory adaptations: vascular counter-current heat exchangers in the flippers, thick subcutaneous insulation beneath its leathery shell and effective inertial homoiothermy, if not endothermy2,3. Whether this ability to maintain a body temperature higher than the ambient is due to endogenous endothermy or thermal inertia remains unclear4,5. The skeleton of Dermochelys remains extensively cartilaginous even in adult animals6,7, which has been attributed to neoteny secondary to its highly pelagic habitat, based on the assumption that its skeleton resembled that of typical embryonic turtles8. However, up to now there have been no studies of the internal architecture of the leatherback appendicular skeleton. We report here that the chondro-osseous morphology of Dermochelys is unlike that of any other known extant turtle or reptile but is more similar to that of marine mammals, notably Cetacea (whales) and Sirenia (manatees).