The Potential Role of Osteoderms during Thermoregulation in the American Alligator

Osteoderms in crocodilians are known to function in mechanical protection, locomotor support, and acid-base regulation. With a rich vascular supply, osteoderms are also thought to play an active role in crocodilian thermoregulation, allowing the animal to absorb or dissipate heat faster than has non-ossified dermis. We tested this hypothesis by monitoring superficial and deep temperatures of juveniles of the American alligator (body mass 0.3-30 kg) during warming and cooling between 15 and 30°C. We recorded skin surface temperatures with an infrared camera, and core temperature with a cloacal thermocouple. We controlled for cutaneous perfusion by running the experiments first on live animals and then on their carcasses. We found, unsurprisingly, that animal size has a significant negative effect on rate of heat exchange. Further, warming (to 30°C) occurred significantly faster in live animals than carcasses, but differences in cooling (to 15°C) were not appreciable. Scales with osteoderms (in the cervical and dorsal regions) showed small (\u3c2°C) differences in temperature profile from neighbouring scales without dermal bone. These temperature differences were most pronounced at the start of each experiment, and disappeared with each experiment duration. Notably, these temperature differences were not consistent between anatomic regions within an animal, or between animals (i.e., scales with osteoderms sometimes showed higher, sometimes lower surface temperature). Importantly, these temperature differences were similar in carcasses. This suggests that heat exchange through the crocodilian skin is dependent more on thermal characteristics of individual scales, and their anatomic location, than on vascular perfusion of underlying tissue, with or without osteoderms