The fossil record of primates is sparse, and many gaps remain in our knowledge. One gap relates to the divergence within the catarrhines — the ancestors of hominoids (apes and humans) and Old World monkeys. The discovery of a previously unknown catarrhine in Saudi Arabia, dated to 29–28 million years ago, helps to fill in some details. This specimen shows very few catarrhine specializations, suggesting that the divergence between Old World monkeys and hominoids must have occurred after this date.
This fossil cranium of a new stem catarrhine from western Saudi Arabia allows palaeontologists to place a more accurate date than previously possible on the divergence of cercopithecoids (Old World monkeys) and hominoids (apes and humans) within Old World higher primates (Catarrhini). The new specimen dates to the mid-Oligocene, around 29 million to 28 million years ago, and has no crown catarrhine specializations other than the presence of a tubular ectotympanic, suggesting that the divergence of Old World monkeys and hominoids happened after that date. The cover shows the anterior view of the cranium, which has its lateral incisors, canines and broad molars in situ. The size of the cranium indicates a medium-sized primate, between 15 and 20 kilograms in body mass. Photo credit: Daniel Erickson/Bonnie Miljour, University of Michigan.
It is widely understood that Hominoidea (apes and humans) and Cercopithecoidea (Old World monkeys) have a common ancestry as Catarrhini deeply rooted in Afro-Arabia1, 2, 3, 4. The oldest stem Catarrhini in the fossil record are Propliopithecoidea, known from the late Eocene to early Oligocene epochs (roughly 35–30 Myr ago) of Egypt, Oman and possibly Angola5, 6, 7, 8,9, 10. Genome-based estimates for divergence of hominoids and cercopithecoids range into the early Oligocene11; however, the mid-to-late Oligocene interval from 30 to 23 Myr ago has yielded little fossil evidence documenting the morphology of the last common ancestor of hominoids and cercopithecoids, the timing of their divergence, or the relationship of early stem and crown catarrhines. Here we describe the partial cranium of a new medium-sized (about 15–20 kg) fossil catarrhine, Saadanius hijazensis, dated to 29–28 Myr ago. Comparative anatomy and cladistic analysis shows that Saadanius is an advanced stem catarrhine close to the base of the hominoid–cercopithecoid clade. Saadanius is important for assessing competing hypotheses about the ancestral morphotype for crown catarrhines1, 12, 13, 14, early catarrhine phylogeny12, 15 and the age of hominoid–cercopithecoid divergence11. Saadanius has a tubular ectotympanic but lacks synapomorphies of either group of crown Catarrhini, and we infer that the hominoid–cercopithecoid split happened later, between 29–28 and 24 Myr ago.
Nature 466, 360–364 (15 July 2010) doi:10.1038/nature09094 Received 15 February 2010 Accepted 16 April 2010
Museum of Paleontology, University of Michigan, 1109 Geddes Avenue, Ann Arbor, Michigan 48109, USA
Iyad S. Zalmout, William J. Sanders, Laura M. MacLatchy, Gregg F. Gunnell, Jeffrey A. Wilson & Philip D. Gingerich
Department of Geological Sciences, University of Michigan, 2534 C. C. Little Building, 1100 North University Avenue, Ann Arbor, Michigan 48109, USA
Iyad S. Zalmout, Jeffrey A. Wilson & Philip D. Gingerich
Department of Anthropology, University of Michigan, 1085 South University Avenue, Ann Arbor, Michigan 48109, USA
William J. Sanders, Laura M. MacLatchy & Philip D. Gingerich
Saudi Geological Survey, Paleontology Unit, PO Box 54141, Jeddah, 21514, Saudi Arabia
Yahya A. Al-Mufarreh, Mohammad A. Ali, Abdul-Azziz H. Nasser, Abdu M. Al-Masari, Salih A. Al-Sobhi,
Ayman O. Nadhra & Adel H. Matari
Contributions
I.S.Z., Y.A.A., M.A.A., A.H.N., A.M.A., S.A.A., A.O.N., A.H.M. and J.A.W. undertook the palaeontological survey, fossil collection and field geology. W.J.S. prepared the fossils. G.F.G., L.M.M. and W.J.S. performed the comparative study and phylogenetic analysis of catarrhine primates. L.M.M. and P.D.G. coordinated the micro-CT scanning. G.F.G. and W.J.S. made comparative studies of the non-primate mammalian fauna and identified the taxa. All authors contributed to the manuscript.
Competing financial interests
The authors declare no competing financial interests.
Corresponding authors
Correspondence to:
Iyad S. Zalmout (zalmouti@umich.edu) or
William J. Sanders (wsanders@umich.edu) or
Philip D. Gingerich (gingeric@umich.edu)
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