Meeting Abstract

57.6  Tuesday, Jan. 6  Evolutionary rates and patterns of artiodactyl limb reduction BORMET, A.K.*; MARCOT, J.D.; SEARS, K.E.; Univ. of Illinois; Univ. of Illinois; Univ. of Illinois bormet1@illinois.edu

Many clades of artiodactyls show evolutionary reductions in the number of distal elements of their limb skeleton, either through the fusion of two bones or the loss of bones entirely. This reduces the limbs distal weight and provides more stability among elements of the distal limb. It is, therefore, likely an adaptation to cursorial locomotion. Cenozoic environmental changes that led to the spread of open environments (e.g., savannas) might have provided an impetus for artiodactyl limb adaptation. To establish the historical pattern of artiodactyl limb reduction, we began by defining 31 characters of artiodactyl limbs that describe the reduction, fusion or loss of elements. We then determined the character states of a sample of living and extinct artiodactyl genera, and mapped these onto a composite phylogeny of artiodactyls to determine the timing of evolutionary changes. We then calculated the rate of evolution of these characters in each of thirty two-million-year-long intervals. There is a considerable peak in evolutionary rate around 38Ma, at the end of the Middle Eocene. Notably, this coincides perfectly with an observed peak in ungulate origination rate suggesting a possible relationship between the radiation of the major groups of living artiodactyls and the reduction of their limbs. The rate of limb evolution gradually declines throughout the Oligocene, but increase again around the Oligocene-Miocene boundary at 23Ma. Interestingly, this coincides with some recent estimates of the spread of grassland ecosystems in North America, suggesting a possible link between environmental change and artiodactyl limb evolution.