Taxonomy of Proconsul: an issue of species numbers or sexual dimorphism?

© 2015 Hugh WeaverI have investigated the alpha taxonomy of Miocene primate genus Proconsul by performing measurements on photographs of fossil dental material obtained from museum sources. My aim was to assess levels of variation, and thereby evidence for sympatric species, by comparing results with those obtained from sex-matched samples of extant hominoids. The holotype of the initial species described, Proconsul africanus, came from a mainland site in western Kenya. Additional examples of the genus were obtained subsequently from adjacent sites and from islands within Lake Victoria. By 1951, three species of progressively-increasing size were recognised, seemingly present at both island and mainland localities. However, subsequent investigations questioned whether, instead of two sympatric species at a particular site, particularly Rusinga Island, size disparities noted reflected the presence of a single sexually dimorphic species. I addressed this debate by comparing results of measurements of 144 Proconsul specimens with those from sex-matched samples comprising 50 specimens each of four extant primate genera: Pan, Gorilla, Pongo and Hylobates/Symphalangus. The protocol consisted of measuring occlusal views of adult molars to obtain linear measurements and cusp areas. By selecting samples on a 1:1 sex-matched basis for extant groups, and matching these against those for Proconsul, I minimised the potential that variations within the Proconsul material reflected sexual dimorphism within one species. I have investigated the situation relevant to each of two clusters of primate fossil sites, respectively on Rusinga and Mfangano Islands (Area 1) and at mainland sites around Koru (Area 2). The study has addressed a null hypothesis: that at each Area, only one Proconsul species was present from the relevant time-horizon. Analyses confirmed that levels of variation within Proconsul, at each of Areas 1 and 2, outweighed those within extant hominoids. More than one species of Proconsul existed contemporaneously at each cluster of Miocene fossil sites