Abstract:
Horse limbs are modified in a distinctive manner. This includes reduction in digits, extension of distal elements with accompanying long tendons, and specific changes in the organization and attachment of the limb musculature. Various functional aspects of this morphology can be evaluated, but interpretation of the suite of characters is dependent to an unfortunate degree on the model being evaluated. Up to now, these modifications have largely been evaluated in the context of speed performance in running, with the expectation that the motivation for the changes in evolution are determined by the risk of predation. Paleontological evidence, however, suggests that these modifications occurred well before pursuit predators existed, leaving the meaning for the equid modifications ambiguous. In this seminar I evaluate the context of the evolution of the horse lineage and identify an alternate pressure that may be responsible for the modifications seen: the exploitation of widely distributed food resources. In this context it is economical transport at a reasonable speed that allows access to the resource and the limb morphology of the horse is evaluated for this role. Analogy is made to several other unrelated species that appear to have acquired parallel functional modifications when faced with the same environmental opportunity, e.g. camels, kangaroos and ostriches. The modifications of the horse limb are evaluated with changes in the dentition that are likely indicative of the digestive strategy of the animal.