LANDRY, S.O.: Bipedal Upright Stance in Ground Sloths.

Measurements in dinosaurs of the estimated height of the heart from the ground suggest that this distance never exceeds about two meters, no matter what the size of the animal. This generalization appears to hold good for all terrrestrial animals. An apparent exception are the giant ground sloths, of which the largest is Megatherium with a weight of approximately five tons (4 tonnes.) The animal is mounted as standing on its hind legs, with bent knees, and its weight partly supported by the tail, a position that would raise its heart considerably above two meters Since this weight is about that of a male African elephant, it seems unlikely that it could assume this position, and even less likely that it could walk bipedally, since this would mean that part of the time, the whole 5 ton load would fall on one bent limb. This would require an unrealisticaly large quadriceps femoris and ventral tail muscle . Three is no basis for the common assumption thatMegatherium browsed off of the tops of trees. It has been argued that circus elephants assume at least a semi-upright, bent-legged position for short periods of time, but these are female, Indian elephants (light weight as elephants go) and anecdotally it is reported that they sometimes break their legs performing this feat. Aramayo (2001) reports trackways of Megatherium that are bipedal. However, there are places along the trackway where the imprint of the manus is also seen, suggesting that the animal was stoooped over so that its thorax was relatively close to the gound during walking, which was done wih straight legs.