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

Abstract

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 endothermy^2,3. Whether this ability to maintain a body temperature higher than the ambient is due to endogenous endothermy or thermal inertia remains unclear^4,5. The skeleton of Dermochelys remains extensively cartilaginous even in adult animals^6,7, 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).