Meeting Abstract
Caudal autotomy, the ability to shed the tail, is common among lizards as a defense mechanism to escape predation. This trait is a basal synapomorphy of Lepidosauria. About two-thirds of extant lizard families include species that retain the ability. Many can also regenerate the tail as a cartilaginous rod. The oldest known fossil evidence of tail regeneration in a squamate comes from a gekkonid specimen from the Late Jurassic Solnhofen deposits (150 Ma) in Germany. This specimen has a truncated tail and an impression of a rod, visible under UV light, where the tail is missing. No other fossil squamate material showing signs of tail regeneration has been previously described. Here I report the first documented evidence of tail regeneration in a derived fossil squamate, a glyptosaurine (Anguidae) lizard from the early middle Eocene Bridger Formation (49~46 Ma) in the Bridger Basin of southwestern Wyoming. The specimen includes a 1.5-cm segment of the tail with in situ imbricate osteoderms. Two rings of larger osteoderms surround the anterior half, and three rows of osteoderms that are 50% smaller surround the posterior half. Autotomized tails in extant anguid lizards also have smaller osteoderms on the regenerated portion of the tail, even when it has regrown to its full length. In the glyptosaurine specimen, the tail diameter past the breakage point is only 65% that of the original half. Extant lizards also exhibit an abrupt decrease in diameter between the original and the regenerating portions of the tail. Computed tomographic scans reveal a caudal vertebra preserved inside the osteoderms, with an intravertebral fracture plane. The scans also reveal a bony callus on the left medial wall of the osteoderms, indicating that the animal sustained an injury or infection as the tail regenerated.
