RISKIN, D.K.*; HERMANSON, J.W.; Cornell University; Cornell University: Independent evolution of quadrupedal locomotion: �Front-wheel drive� in the bounding gait of vampire bats

Most of the >1,000 species of bats are poor walkers, with the exception of a few disparate taxa that crawl well, such as the vampire bats. The fossil record does not indicate whether vampire bats have secondarily evolved walking, or whether they retained it throughout their evolution as bats. Here, we present kinematic data which suggest that vampires lost, and subsequently regained the ability to crawl well. Using a high-speed camera (250 Hz) and a variable-speed treadmill, we observed two symmetric gaits used by Common Vampire Bats (Desmodus rotundus). At speeds of 0.12 to 0.28 m�s^-1, D. rotundus used a walking gait, and at speeds of 0.56 to 1.14 m�s^-1 used a bounding one. At intermediate speeds both gaits were used (n=61). The walking gait was similar to that used by other terrestrial vertebrates, but with the duty factor of the forelimbs (mean 73%) greater than that of the hindlimbs (62%) (P<0.0001, n=26), the result of longer forearms compared with hindlimbs. In the bounding gait, whereby a bat repeatedly landed on its hindlimbs, rocked forward to the forelimbs, lifted the legs, and pushed off the ground with the carpus and pollex, the duty cycle of the forelimbs (63%) was again greater than that of the hindlimbs (41%) (P<0.0001, n=20). This footfall pattern matches that described for other bounding mammals, but with the roles of the fore- and hindlimbs reversed. We hypothesize that the selective pressures which favoured the evolution of bounding in other mammals favoured its evolution in a poorly crawling vampire ancestor, and that the role of force production for a bound— accomplished by the hindlimbs in most mammals— was taken up by the wings, which in bats are elongated and possess relatively more muscle mass than the legs.