The forelimb of early Miocene Sloths (Mammalia, Xenarthra, Tardigrada): morphometry and functional implications.

TOLEDO, NESTOR; BARGO, MARÍA SUSANA; CASSINI, GUILLERMO HERNÁN; VIZCAÍNO, SERGIO FABIÁN

Punta del Este -Uruguay

Congreso; 9th International Congress of Vertebrate Morphology; 2010

Universidad de La República - International Society of Vetebrate Morphologyst

The early Miocene sloths are represented by a diversity of small to medium sized forms ranging from 40 to 100 kg. Their forelimbs bones differ in shape from those of their closest living relatives (of approximately 10 kg), Bradypus and Choloepus. Such difference in shape could be related to differences in the biological role of the limb, including locomotion. In order to detect putative patterns related to locomotion, 32 linear measurements were defined and taken on the forelimb bones. The sample was composed of 7 complete specimens of fossil sloths (Hapalops and Eucholaeops) and 126 specimens of living mammals (marsupials, xenarthrans, pangolins, rodents, primates, and carnivorans), including either arboreal or terrestrial and digging taxa. Principal Components Analyses were performed on logarithms of original measurements. The first three PCs accounted for 90.3 % of the cumulative variability. PC1 roughly represented body size, while negative values of PC2 represented mechanical improvement for digging habits, such as a long olecranon process. Positive values of PC3 represented variables that could be related to prehension capability, such as a wide distal humerus (among others). Fossil sloths were clearly separated from living ones, sharing a common morphospace with anteaters and other good diggers. Conversely, living sloths shared a morphospace with primates. These results suggest that fossil sloths have a different locomotor pattern than extant ones, probably more similar to vermilinguans and pangolins, including  putative good digging capabilities and/or semiarboreal habits. Substrate use seems to be interfering in the analysis of locomotion pattern based on forelimb morphology.