The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


First known tarsals of the earliest primate Purgatorius

STEPHEN G. B. CHESTER1, JONATHAN I. BLOCH2 and WILLIAM A. CLEMENS3.

1Department of Anthropology, Yale University, 2Florida Museum of Natural History, University of Florida, 3University of California Museum of Paleontology, University of California, Berkeley

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Earliest Paleocene Purgatorius has traditionally been considered the most primitive known primate based on its age, dental morphology, and plesiomorphic lower dental formula (3.1.4.3). However, its primate (or even placental) affinities have been questioned based on results from recent phylogenetic analyses that suggest a relationship with primitive condylarths including contemporary Protungulatum. The fossil record of Purgatorius has been limited to isolated teeth and fragmentary dentitions, with little data relevant to hypotheses of relationships or primitive primate ecology. Isolated tarsals found in the same deposits as hundreds of dental specimens of Purgatorius from the earliest Paleocene (~65MYA) of the Garbani Channel fauna localities, Garfield County, Montana, are referred to Purgatorius based on size, abundance, diagnostic similarities to dentally-associated tarsals of euarchontans (generally) and plesiadapiforms (specifically). Purgatorius differs from Protungulatum in having astragali with a longer, narrower trochlea that extends distally onto the neck, confluent sustentacular and navicular facets, and a more pronounced medial side of the head; and calcanea with a more proximodistally aligned ectal facet, a helical sustentacular facet that extends distally onto the body, a circular and concave cuboid facet, and no fibular facet. These characteristics are consistent with a mobile ankle capable of pedal inversion to adjust to an uneven substrate in Purgatorius, whereas Protungulatum is better suited for a more level substrate. We suggest that tarsals of Purgatorius are most similar to those of micromomyid plesiadapiforms, reconstructed as arboreal based on fairly complete skeletons, and that Purgatorius lies near the ancestry of all primates within Euarchonta.

This study was funded by a National Science Foundation Dissertation Improvement Grant (SBE-1028505 to Eric Sargis and S.G.B.C.), a Leakey Foundation Research Grant (S.G.B.C.), and by the Doris O. and Samuel P. Welles Research Fund, University of California Museum of Paleontology.

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