Meeting Abstract
The Equidae belong to the Perissodactyla, which are also known as the odd-toed ungulates. During the Miocene, at least four different lineage within the Equidae reduced the number of functional digits on the forelimb to one, also referred to as monodactyly. The Equus lineage, including asses, donkeys, horses and zebras, is the only remaining lineage. This study is part of a larger project that will test hypothesis regarding monodactyly and the disappearance of the three extinct lineages. The aim of this cadaver study is to compare the instantaneous axis of rotation (IAR) of all forelimb joints between different monodactyl equids. The IAR can be used to describe the three-dimensional motion of two subsequent segments. Cadaver forelimbs of a przewalskii, a zebra, different horse breeds and several non-equids (including an alpaca, a lion and a tapir) were used to determine the IAR over the entire range of motion for all forelimb joints. Standardized cuts were made at the midlevel of each segment and bone pins attached with reflective marker triads were drilled into the forelimb bones. Each forelimb joint was manually moved independently through flexion-extension, abduction-adduction and internal-external rotation. The three-dimensional coordinates of the marker triads were recorded using an infra-red six camera system. With a customized MATLAB script, based on the software package KineMat, IAR properties were calculated over the entire range of motion. Within the monodactyl species, the different joints displayed different IAR behaviours, but for each joint the IAR properties were similar between the different monodactyl species. Comparable orientations and positions of the IAR suggest that different species can display similar movements between the different forelimb segments, and thus similar kinematics.
