Meeting Abstract

102.3  Wednesday, Jan. 7  Developmental Evolution of the Anuran Sacrourostylic Region and its Locomotory Implications PUGENER, L. Analia; MAGLIA, Anne M.*; Missouri Univ. of Science and Technology, Rolla magliaa@mst.edu

In this talk, we discuss the developmental evolution of the sacrourostylic complex of frogs as it relates to locomotion. The sacrourostylic region is one of the most unusual specializations of the anuran skeleton, and seems to have appeared concomitant with the origin of the group and the move toward saltation. The ontogenetic pathway that forms the adult sacrum and urostyle subsequently evolved several times, apparently in association with varied locomotory modes. In some taxa, the hypochord does not extend anteriorly beyond Postsacral Vertebra 1, whereas in others it extends anteriorly to the level of the sacrum. Thus, as the hypochord migrates dorsally during metamorphosis, it fuses to either Postsacral Vertebra 1 or to the sacrum. In the first case, the adult morphology consists of an articulating sacrum and urostyle, as is the case for jumping frogs such as Acris crepitans and Discoglossus sardus. In the second case, the adult morphology results in a fused sacrum and urostyle, which is characteristic of the burrowing Spea multiplicata and the aquatic Xenopus laevis. A moveable articulation (especially a bicondylar one) between the sacrum and urostyle constitutes the best joint for saltatorial locomotion, whereas a fusion of these elements increases stability for swimming and digging. Further rigidity in the sacrourostylic complex, which helps maintain a streamlined position during swimming, is achieved by fusion of additional vertebra(e) to the sacrum and urostyle (forming a synsacrum), as in Hymenochirus curtipes.