title: Palaeontological evidence for an Oligocene divergence between Old World monkeys and apes.
abstract: Apes and Old World monkeys are prominent components of modern African and Asian ecosystems, yet the earliest phases of their evolutionary history have remained largely undocumented. The absence of crown catarrhine fossils older than ∼20 million years (Myr) has stood in stark contrast to molecular divergence estimates of ∼25-30 Myr for the split between Cercopithecoidea (Old World monkeys) and Hominoidea (apes), implying long ghost lineages for both clades. Here we describe the oldest known fossil 'ape', represented by a partial mandible preserving dental features that place it with 'nyanzapithecine' stem hominoids. Additionally, we report the oldest stem member of the Old World monkey clade, represented by a lower third molar. Both specimens were recovered from a precisely dated 25.2-Myr-old stratum in the Rukwa Rift, a segment of the western branch of the East African Rift in Tanzania. These finds extend the fossil record of apes and Old World monkeys well into the Oligocene epoch of Africa, suggesting a possible link between diversification of crown catarrhines and changes in the African landscape brought about by previously unrecognized tectonic activity in the East African rift system.
authors.affiliation: Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio 45701, USA. stevensn@ohio.edu
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Stevens
authors.forename: Erik R
authors.initials: ER
authors.lastname: Seiffert
authors.forename: Patrick M
authors.initials: PM
authors.lastname: O'Connor
authors.forename: Eric M
authors.initials: EM
authors.lastname: Roberts
authors.forename: Mark D
authors.initials: MD
authors.lastname: Schmitz
authors.forename: Cornelia
authors.initials: C
authors.lastname: Krause
authors.forename: Eric
authors.initials: E
authors.lastname: Gorscak
authors.forename: Sifa
authors.initials: S
authors.lastname: Ngasala
authors.forename: Tobin L
authors.initials: TL
authors.lastname: Hieronymus
authors.forename: Joseph
authors.initials: J
authors.lastname: Temu
mesh_terms: D000818:Animals; D002520:Cercopithecidae / Q000033:anatomy & histology / Q000145:classification*; D005580:Fossils; D049690:History, Ancient; D015186:Hominidae / Q000033:anatomy & histology / Q000145:classification*; D008334:Mandible / Q000033:anatomy & histology; D010802:Phylogeny; D013636:Tanzania; D014070:Tooth / Q000033:anatomy & histology