New cranial material of Notharctus (Mammalia, Primates, Notharctidae) from the Sheep Pass Formation, Elderberry Canyon, Nevada, with implications for incisor morphology and paleogeography of notharctine primates

ABSTRACT

A new specimen, referred to the notharctid primate Notharctus tenebrosus, is described from the middle Eocene of eastern Nevada. The material consists of the upper and lower jaws with most tooth loci represented, including rare representation of relatively unworn upper incisors. The completeness of the specimen permits a restoration of the spatial relationships of the anterior teeth, demonstrating that there was a small zone of interproximal contact between the upper central incisors. The relatively unworn upper incisors also indicate a unique cropping mechanism in notharctids not seen before in the group. The orientation of the cropping edges on the upper central incisors changed progressively with tooth wear, implying a shift in function and/or food properties over the course of dental senescence. The provenience of the specimen highlights the wide geographic distribution of this extinct primate species.

ACKNOWLEDGMENTS

For assisting R.J.E. in uncovering and collecting blocks of fossiliferous limestone from the Nevada site during several expeditions, we thank D. Chaney, F. Grady, J. Flynn, and A. Lewis. The time-consuming and tedious process of preparing the specimens from limestone matrix in dilute formic acid was carried out principally by D. Chaney and F. Grady. We thank D. Boyer, J. Thostenson, C. Crawford, H. Kristjanson, and E. St Clair for help with μCT scanning of the specimen (sponsored by NSF BCS 1304045 to D. Boyer and E. St Clair). Scans of comparative material were kindly provided by D. Boyer and are available through morphosource.org (sponsored by NSF BCS 1552848 to D. Boyer, 1440742 to D. Boyer and G. Gunnell, and 1440558 to J. Bloch). J.M.G.P. thanks the Smithsonian National Museum of Natural History (especially N. Pyenson) for the opportunity to borrow the specimen described here and for the chance to make comparisons with other notharctids in the collection. We thank E. St Clair and K. Rose for thoughtful discussion of the significance of this specimen and of notharctids in general. We thank reviewers L. Marivaux and A. Le Cabec as well as the editorial staff of the journal for their assistance in improving the manuscript.