Morphology and locomotor adaptations of the bovid femur in relation to habitat

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Abstract
Extant bovids inhabit a wide diversity of environments that range from forest to savanna and display locomotor patterns that are habitat specific. I report here on an investigation of the linkage between these locomotor patterns and habitat based on a study of the morphology of the bovid femur. Femoral head shape, shaft dimensions, and knee structure are examined and support a statistically significant separation of the different morphological complexes present in bovids from forest, broken cover, and savanna habitats. Morphological differences are primarily related to locomotor patterns as reflected in the degree of cursoriality displayed by bovids in different habitats. Cursorial bovids from savanna environments have laterally expanded femoral heads that act to limit the degree of abduction and axial rotation at the hip, and elliptically shaped distal femora that increase the moment arm of the extensor muscles that cross the knee. Forest bovids have spherically shaped femoral heads. This morphology permits a much higher degree of abduction and axial rotation at the hip and appears to provide greater maneuverability in a vegetationally complex habitat. Bovids living in broken cover environments that fall between the extremes of closed canopy forest and savanna display an intermediate set of femoral characters. This approach to the relationship between habitat and locomotion offers a potentially powerful means with which to examine the interplay between structural form and function in bovid evolution.