Meeting Abstract
Morphological divergence in the forelimbs is often associated with functional habits exhibited by the Xenarthra as a clade, ranging from arboreal-suspension in sloths to terrestrial-digging in armadillos. We hypothesized that quantitative differences in hindlimb form also will be predictive of the lifestyles observed among xenarthrans. A total of 27 functional indices were calculated from 42 measurements of bone length, width, and depth from a sample of N=83 skeletal specimens (total: 19 species). All raw data were initially log-transformed to account for allometry. Index data were evaluated using Principal Component Analysis (PCA) and corrected with phylogenetic PCA to determine the osteological correlates among extant taxa, and were subsequently used to predict substrate preference and substrate use by discriminant function analysis. PCA on index data clearly separated sloths from armadillos in morphospace based on gracility versus robustness, respectively, of hindlimb skeletal elements, whereas these characteristics were intermediate in anteaters. With the exception of hip moment index (HMI) and tibial tuberosity index (TTI) being associated with generalized traits in mammals, separation patterns were largely similar after accounting for phylogenetic relatedness among taxa. The predicted memberships for substrate preferences and uses for each species almost invariably corresponded with their observed lifestyles, with several indices relating to knee articulation stability and ankle/limb mechanical advantage as the significant discriminating features. Overall, our assessments expand interpretations of limb form and functional habits exhibited among xenarthrans, and potentially identify several conserved traits related to fossorialty as well as morphological trade-offs between digging and climbing.
