Anais do I Simpósio Brasileiro de Morfologia Comparada de Vertebrados

Sloths constitute a successful radiation of South American mammals, with posterior dispersal to Central and North Americas, including the Caribbean Islands. Representatives of the group are known from the Late Eocene to the present, but almost all species are currently extinct. Most of the taxonomic diversity of sloths is included in two major clades, Megatherioidea and Mylodontoidea. However, the patterns of morphological disparity for those clades remain understudied, and are investigated here.
We calculated a distance matrix using a cladistic morphological dataset with 429 characters for 38 megatherioid and 28 mylodontoid sloths. The distance matrix was ordinated with a Principal Coordinates Analysis to produce bivariate plots. We applied three disparity metrics, each for a different aspect of data distribution in morphospace - volume (Sum of Variances), density (Average Nearest Neighbour Distances), and displacement (Average Displacement). To assess significance for differences in disparity, data was submitted to 1000 bootstrap pseudoreplications and evaluated with a Wilcoxon Rank-Sum Test.
Our results show that the separation of Megatherioidea and Mylodontoidea in morphospace was mostly represented by PCoA1. In this axis, we also observed that Choloepus occupy an intermediate position between the two groups, but closer to the megatherioids. Megatherioidea and Mylodontoidea present significantly different patterns of morphospace occupancy, except for the density metric. The volume occupied by Megatherioidea is greater, whereas Mylodontoidea shows a greater displacement relative to the morphospace centroid. Further studies should be conducted to elucidate if those patterns of disparity can be associated with historical and/or ecological factors.