Locomotion in the Fossil Vulture Teratornis

Abstract

Various parts of the skeleton of the large Pleistocene vulture, Teratornis merriami, have been found in deposits in the southern United States, from California to Florida, and in Mexico. Nowhere are the remains as numerous or as well preserved as in the asphalt deposits of Rancho La Brea in southern California. It was this abundance and preservation of entire bones that made possible this study of its locomotor apparatus. I am grateful to the Los Angeles County Museum, Los Angeles, California, for the use of its facilities and specimens. Teratornist merriami has been placed in a family distinct from, and yet closely related to, the family Cathartidae, the New World vultures. Many of the bony parts, the synsacrum, tibiotarsus, tarsometatarsus, coracoid, ulna and metacarpus are typically cathartid with little except size to distinguish them from the Recent condors, Vultur gryphus and Gymnogyps californianus. The skull and sternum are not cathartid in character although there are points of resemblance. The humerus has several peculiarities not found in the New World vultures. The gross similarities of certain wing elements of the tertatorn to those in the cathartids have led to the suggestion that Teratornis was similar in its flight pattern, that is, that it was chiefly a soaring bird. There are few specific features to uphold this contention. It is known that Gymnogyps californianus, the California Condor, on level ground must run or hop for several yards to gain enough momentum to lift its weight into the air. It also needs to flap several times as it leaves the ground. If Teratornis had a similar type of wing, its run for the takeoff must have been even longer because of its greater weight. However, we find that its wing was shorter in relation to its body weight (Table 1), and its legs were much shorter than in Gymnogyps (Table 9). Its leg bones are more delicate distally. With such poor adaptations for running, a long run for the takeoff would have been an arduous, if not impossible, task. It seems likely that Teratornis was able to leave the ground by use of its wings more easily than can the present California Condor. Miller (The Birds of Rancho La Brea, Publ. 349, Carnegie Inst., Washington, 1925) has wondered how Teratornis with its weak legs, soaring wings and great weight took off from a level surface. Such a combination of characters and terrain would seem to make the takeoff almost impossible. One possibility is that Teratornis lived exclusively in areas of cliffs and slopes where easy travel downhill would be sufficient to gain speed for soaring flight; this appears unlikely. I think it more probable that Teratornis rose from the ground by vigorous flapping of its wings. The body weight of the teratorn compared with that of any other flying bird must have been enormous. An attempt to get a gross estimate was made by determining the areas of the sternum and synsacrum in Haliaeetus and 725