Dietary ecospace and the diversity of euprimates during the Early and Middle Eocene

This study examined adapoid and omomyoid euprimate dietary and body size diversity from the Eocene of North America and Europe. Estimates of body weights and shearing quotients calculated from lower molars were plotted on a coordinate graph as a representation of dietary niche space (dietary ecospace) occupied by extinct species. By computing the areas, average intertaxon distances, and average distances from the centroid of the resulting polygons, comparisons of Eocene euprimate dietary and body size diversity were made. Results indicate that euprimate dietary niche space expanded significantly in North America from the Early to Middle Eocene, and at all times during the Early and Middle Eocene, the niche space occupied by North American euprimates exceeded that of corresponding European euprimates. These results confirm that fossil euprimate diversity, as measured by diet and body size, significantly differed across biogeographic areas. There are many possible explanations as to why North American euprimates were significantly more diverse in terms of diet and body size than their European counterparts. The explanation advocated here as most responsible for the increased diversity during the Early and Middle Eocene relates to the existence and increased sampling of more ecologically diverse environments, such as basin margins in the western interior of North America. These diverse environments could have promoted biological processes that led to the generation of increased diversity in North America compared to the isolated island refugia of Western Europe during this time.