The anatomy and systematic position of the early Miocene proconsulid from Meswa Bridge, Kenya Terry Harrison a, * , Peter Andrews b a Center for the Study of Human Origins, Department of Anthropology, New York University, New York, NY 10003, USA b Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK article info Article history: Received 26 June 2008 Accepted 22 February 2009 Keywords: Proconsul meswae Fossil apes East Africa Muhoroni Agglomerates Dentition Phylogeny abstract A small collection of fossil catarrhines was recovered from the early Miocene locality of Meswa Bridge in western Kenya between 1978 and 1980. The associated fauna from Meswa Bridge indicates an age older than 20 Ma. Much of the material has been briefly described previously, and its taxonomic status considered. The material can be assigned to a minimum of four individuals, all of which are infants or juveniles. Although the specimens were shown to belong to a distinct species of Proconsul, the taxon was not named, primarily because many of the specimens belonged to immature individuals. Nevertheless, the combined morphological features of the deciduous and permanent teeth allow the diagnosis of a new species of Proconsul, which is formally named here as P. meswae. It is a large-sized species, similar in dental size to P. nyanzae. The main features distinguishing it from all other previously named species of Proconsul are: incisors and deciduous incisors relatively low crowned; upper deciduous canines relatively higher crowned and more robust; molars and deciduous premolars relatively broader and higher crowned, with a more pronounced degree of buccolingual flare and better developed cingula; size differential between molars not as marked; dP 4 with a longer mesial fovea and smaller hypoconulid and distal fovea; P 4 relatively broader, with a better developed buccal cingulum; lower molars less rectan- gular with a longer mesial fovea, smaller distal fovea, more restricted talonid basin, and a tendency for a smaller hypoconulid; dP 4 and upper molars with strongly buccolingually splayed roots; mandibular corpus in infants relatively deeper and more slender; maxilla with a well developed canine jugum and fossa. The broader and more flared molars with better developed cingula indicate that the Meswa Bridge species is more primitive than other species of Proconsul. The inference that it is a stem member of the Proconsul clade is consistent with the estimated age of the material. Ó 2009 Elsevier Ltd. All rights reserved. Introduction Excavations at the early Miocene locality of Meswa Bridge in western Kenya between 1978 and 1980 yielded a small collection of cranio-dental specimens of a large catarrhine primate (Table 1). Faunal and stratigraphic correlations indicate an age of older than 20 Ma, making it one of the oldest localities in East Africa with fossil catarrhines. Andrews et al. (1981) briefly described the material, and concluded that the specimens could all be referred to a single species of Proconsul. Although Andrews et al. (1981) recognized the distinctiveness of the material compared with all other named species of Proconsul, they deferred naming a new species because most of the specimens from Meswa Bridge were from infants and juveniles. Since few immature individuals of other species of Proconsul are known, any attempt to differentiate a new species based solely on comparisons of the deciduous dentition could prove problematic. However, there are sufficient examples of the permanent dentition from Meswa Bridge, which, when used in conjunction with the deciduous teeth, provide an adequate basis to justify the diagnosis of a new species. The aim of this paper, therefore, is to present a detailed description of the specimens from Meswa Bridge (including several specimens that were not included in the original study by Andrews et al. ([1981]), and to compare the material with the currently recognized species of Proconsul. Based on these comparisons, we show that the Meswa Bridge specimens are distinctive enough to be recognized as a new species of Proconsul, P. meswae. Although the relationships between the different species of Proconsul have not yet been fully resolved, it is possible to infer, based on a number of primitive features in the dentition, that P. meswae is the primitive sister taxon of the other species of Proconsul. This is consistent with it being the oldest known species of Proconsul. * Corresponding author. E-mail address: terry.harrison@nyu.edu (T. Harrison). Contents lists available at ScienceDirect Journal of Human Evolution journal homepage: www.elsevier.com/locate/jhevol 0047-2484/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jhevol.2009.02.005 Journal of Human Evolution 56 (2009) 479–496