A new species of the archaic primateZanycterisfrom the late Paleocene of western Colorado and the phylogenetic position of the family Picrodontidae

Benjamin John Burger

doi:10.7717/peerj.191

Abstract

A new species of an archaic primate (Pleisadapiformes) is described based on a maxilla containing the first and second upper molars from the Fort Union Formation, Atwell Gulch Member in northwestern Colorado. The preserved teeth show the unusual dental characteristics of members of the rare and poorly documented Picrodontidae family, including an elongated centrocrista and wide occlusal surface. The new species is placed within the genus Zanycteris (represented by a single specimen from southern Colorado). This placement is based on similarities in regard to the parastyle, curvilinear centrocrista, and wider anterior stylar shelf on the upper molars. However, the new species differs from the only known species of Zanycteris in exhibiting an upper first molar that is 30% larger in area, while retaining a similarly sized upper second molar. Phylogenetic analysis supports the separation of the Picrodontidae family from the Paromomyidae, while still recognizing picrodontids position within Pleisadapiformes. The unusual dental features of the upper molars likely functioned in life as an enhanced shearing surface between the centrocrista and cristid obliqua crests for a specialized diet of fruit. A similar arrangement is found in the living bat Ariteus (Jamaican fig-eating bat), which feeds on fleshy fruit. The new species showcases the rapid diversification of archaic primates shortly after the extinction of the dinosaurs during the Paleocene, and the unusual dental anatomy of picrodontids to exploit new dietary specializations.

Highlights

The family Picrodontidae consists of rare fossil mammals known only in the late Paleocene (Torrejonian and Tiffanian North American Land Mammal Ages (NALMA)) of North America
This paper reports on the occurrence of a new species of Zanycteris discovered in the late Paleocene (Tiffanian) deposits of the Fort Union Formation, Atwell Gulch Member in northwestern Colorado, and discusses the phylogenetic relationship of picrodontids among various groups of archaic primates living in North America during the Paleocene
The members of the Picrodontidae are exceptional in the development of a dentition that maximizes the shear forces along the long contact between the centrocrista on the upper molar and the cristid obliqua that spans much of the length of the elongated talonid basin of the lower molar (Szalay, 1968)

Summary

Introduction

The family Picrodontidae consists of rare fossil mammals known only in the late Paleocene (Torrejonian and Tiffanian North American Land Mammal Ages (NALMA)) of North America. There is a close resemblance between Zanycteris and some of the fruit-eating bats of the New World, such as the living genus Ariteus (Jamaican fig-eating bat). This morphological similarity is exhibited in the upper first molar which is broadly shaped and greatly expanded. How to cite this article Burger (2013), A new species of the archaic primate Zanycteris from the late Paleocene of western Colorado and the phylogenetic position of the family Picrodontidae. More recently studies have positioned the enigmatic Picrodontidae as aberrant members of archaic primates (Szalay, 1968). Researchers have viewed picrodontids as stemming from a Purgatorius-like ancestor (Tomida, 1982), a Palaechthon-like ancestor (Szalay, 1968) or more derived members of the Paromomyoidea (Szalay, 1968; Silcox, 2001; Silcox & Gunnell, 2008)

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