Macrauchenia patachonica Owen, 1838: Limb bones morphology, locomotory biomechanics, and paleobiological inferences

Abstract

Macrauchenia patachonica Owen, 1838 was among the last and largest litopterns, an extinct order of South American native ungulates. Macrauchenia patachonica had anatomical peculiarities as extremely retracted nasals, enlarged cervical vertebrae, and limb bones proportions without good living analogs that lead to asking about its paleobiology. To quantitatively assess the strange combination of limb bone features in M. patachonica, we constructed an indicator of differences in anatomical adaptations for efficient running between forelimb and hind limb (IDFH). We also made a multivariate analysis using data on osteological ratios of living mammals and two other litopterns. We discuss several biomechanical and paleobiological implications of the striking differences between hind limb and forelimb design in M. patachonica. Our main suggestion is that M. patachonica, during fast locomotion, probably used a posture with the neck in a horizontal position.