Meeting Abstract
Anteaters, armadillos, and sloths each have distinctive body plans, yet they are all members of the basal superorder Xenarthra due in part to a number of shared anatomical characteristics about their skull and spine. Divergence in their morphology is associated with the functional habits they exhibit ranging from suspensory locomotion in sloths to fossorial scratch-digging in armadillos. We hypothesize that quantitative differences in hindlimb form will be predictive of the locomotor habits observed among xenarthrans and help to resolve the influences of morphology vs. phylogeny in their present classifications. Comparative analyses were performed on a sample of N=45 skeletal specimens comprising 14 species. A total of 24 functional indices were calculated from 45 raw linear measurements of bone length, width, and depth, and these metrics were evaluated using PCA to determine osteological correlates among extant taxa. Preliminary results show that the first two PCs accounted for 54% of the cumulative variance with the greatest separation of genera along PC1. In general, armadillos shared morphospace, and all have robust femora/tibiae, wide epiphyseal condyles, and a broad tibial tuberosity. These characteristics are intermediate in the anteaters, while sloths have longer, more gracile bones with reduced (or absent) bony protuberances. In addition, there was notable separation along PC2 between two-toed and three-toed sloths, where Bradypus is associated with positive values representing shorter limb length but longer hindfoot elements. Future analyses will: evaluate the influence of allometry and mass on the observed trends of post-cranial morphology, identify features that best predict substrate preference/use, and further resolve evolutionary relationships among xenarthrans.
