BERTRAM, J E A; HERMANSON, J W; Univ. of Calgary, Calgary; Cornell Univ., Ithaca: Transport and transitions on arid grasslands: equine function

It has recently been observed that the standard adaptive explanation for many of the striking morphological features of horses do not necessarily stand up to close scrutiny. Elongate distal limbs with unguligrade stance and reduced digits have often been interpreted within the context of high running speeds associated with successful predator avoidance in open habitats. This is problematic when it is observed that swift pursuit predators did not exist in the environments inhabited by ancestral horses when the lineage began displaying these limb modifications. If not to allow high speed running using a galloping gait, what is the function of these limb modifications? We evaluate the modern equine limb musculoskeletal system within the context of an alternative interpretation of this animal�s functional capability; that of long distance economical travel. Features of the limb skeletal organization and muscular architecture are evaluated via their functional role in locomotion. The relationship between the specific adaptive features and the mechanics involved with the walk, trot and galloping gaits are evaluated. In vivo measurements of muscle function are combined with whole body metabolic cost to generate an alternative view of what the modifications that characterize the horse lineage can accomplish. Supported by NSF IBN 9819985.