Limb posture and gait in Numidotherium koholense, a primitive proboscidean from the Eocene of Algeria

The tapir-sized late Early Eocene proboscidean, Numidotherium koholense , is the oldest known member of the mammalian order to which the living elephants belong. Morphology of the limb skeleton is reviewed and newly discovered elements are described, with emphasis placed on features considered to have a bearing on limb posture and locomotion. Structure of the shoulder joint and the fact that the antebrachium is fused in a supinated position, indicates that forelimb posture would have been of the abducted or semi-sprawling type. The carpus, while exhibiting the typically proboscidean serial arrangement of carpals (no contact between unciform and lunar), also possesses a free os centrale. The presence of an os centrale and entepicondylar foramen in the humerus are unexpected eutherian plesiomorphies. The structure of the hip joint indicates an abducted hindlimb posture. In both the fore- and hindlimb, mechanisms exist at the major joints to cope with the complicated flexion-extension paths typical of a semi-sprawling gait. Both the carpus and tarsus are indicative of a plantigrade stance. This, in concert with an abducted limb posture, indicates that the gait in numidotheres contrasts markedly with the sub-unguligrade, parasagittal gait of elephantiform proboscideans. The recent suggestion that Proboscidea have their origins in a cursorially adapted phenacodontid-like stock receives no support from this analysis.