Athena Review Vol.2, no.3: Eosimias: Asian Roots for Anthropoids

Athena Review: Vol.2, no.3

Recent Finds in Archaeology: Asian Roots for Anthropoids

Further steps in identifying Eosimias

In previous decades, evidence for early anthropoids (the group including all living and extinct monkeys, apes, and humans) came predominantly from northern Africa. Notable finds included the Oligocene's Aegyptopithecus in Egypt's Fayum region dating about 36-25 million years ago. While many known phylogenetic links exist between Aegyptopithecus and an abundant range of later, Miocene, primates found in Africa and Asia, until recently there was little data on ties with the earlier primates of the Eocene era.

A few years ago in 1994-96, caves in central China revealed the first evidence of a 45-million- year-old primate named Eosimias or "Dawn Ape" by discoverers K.C. Beard of the Carnegie Institute and colleagues from the Beijing Institute of Verterbrate Paleontology and Paleoanthropology (AR 1,1). While preliminary findings of Eosimias were limited to a few tiny teeth and jaw fragments, it was enough for Beard and his IVPP colleagues to suggest a Middle to Late Eocene emergence in eastern Asia of the mosaic of traits leading from primitive to anthropoid physiology. This has been further supported by more recent evidence reported in the journal Nature of new findings in China of an Eosimias leg and foot bones, which are claimed to exhibit diagnostic anthropoid traits.

Fig.1: Skeletal anatomy of the left hindfoot of a moern tree shrew, Ptilocercus, with tarsal or ankle bones resembling Paleocene primate Plesiadapidae (after LeGros Clark 1971).]

More recently, fossil teeth and jaw fragments found in 1996-98 in Myanmar (Burma) in southeast Asia have provided further evidence that higher primates may have originated in Asia. The 40-million-year-old Bahinia pondaungensis, a tarsier-like tree-dweller and insect eater the size of today's smallest monkey, has been classified by Jean-Jacques Jaeger of France's Université Montpellier-II as an anthropoid.

The Bahinia remains consisted of two upper jaws and one lower jaw, each with several teeth. Strong similarities between the dentition of Bahinia and the somewhat earlier Eosimias from central China enabled Jaeger to identify Bahinia as an anthropoid. The prosimian-like Bahinia may show a connection between higher primates and the ancestors of modern tarsiers. With the Bahinia fossils were found those of the previously known Amphipithecus, which Jaeger believes to be a more anatomically advanced anthropoid. Jaeger proposes the primitive nature of both Bahinia and Eosimias shows a much earlier origin of anthropoids in Asia by 55-60 million years ago.

[Beard et al., Science 270, 10 Nov.1995; Bower, Science News 156, 16 Oct. 1999; Gebo et al., Nature 404, 16 March 2000; Le Gros Clark, W.E. 1971, The Antecedents of Man, Edinburgh.]

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