DIVING DISEASE IN MARINE REPTILES FROM THE CRETACEOUS TO THE PRESENT

Recognition of diving disease in mosasaurs, ichthyosaurs, plesiosaurs and turtles was based upon identification of avascular necrosis. The devitalized bone typically becomes necrotic (and lucent to x-rays), secondary to loss of vascular supply. Resultant loss of mechanical integrity makes the surface susceptible to compression stresses across joints. The resultant damaged bone can no longer resist the normal stresses across the joint and partly collapses, producing a visible subsidence zone. Vertebrae and proximal portions of humeri and femora and cross-sections of vertebrae of marine reptiles were examined in the major collections of North America, Europe and the Middle East. Avascular necrosis was invariably present in Platycarpus, Tylosaur, Mosasaurus, Plioplatecarpus, Prognathodon, Hainosaurus and Antarctic mosasaur, and invariably absent from Clidastes, Ectenosaurus, Globidens, Halisaurus and Kolposaurus. Frequency was indistinguishable among Ophthalmosaurus, Ichthyosaurus, Temnodontosaurus and Platypterygius, but significantly greater than in Leptonectes, while Stenopterygius was spared. The frequency was indistinguishable among Pliosauridae and Plesiosauridae, with exception of absence in Cryptoclididae. No phyletic trend was evident, as avascular necrosis was seen in some of the earliest plesiosaurs, as well as the last (Elasmosauridae). Avascular necrosis was present in 8 families of marine/aquatic turtles from the Cretaceous to Recent. Desmatochelyidae, Toxochelyidae, Protostegidae and Pleurosternidae were especially afflicted in the Cretaceous. Subsequent reduction in frequency of avascular necrosis in the early Eocene was followed by near disappearance, subsequent to the Oligocene. Contemporary representation is limited to its extremely infrequent occurrence in Cheloniidae (Lepidochelys), Chelydridae (Chelydra and Macroclemys) and Kinosternidae (Kinosternon). The occurrence of avascular necrosis segregates according to diving habits. It is uniformly present in supposed deep divers and uniformly absent in the shallow habitat group, thus providing a window to ancient behavior and to time course of development of mechanisms designed to protect from this disease.