A New Species of Gomphos (Glires, Mammalia) from the Eocene of the Erlian Basin, Nei Mongol, China

Brian P Kraatz,Xijun Ni,Daniel L Gebo,Jin Meng,K Christopher Beard,Yuanqing Wang

doi:10.1206/673.1

Abstract

Dental and postcranial specimens of Gomphos shevyrevae, sp. nov., from the lower part of the Irdin Manha Formation at the Huheboerhe locality, Erlian Basin, Nei Mongol (Inner Mongolia), are described. The new species differs from G. elkema and G. ellae in having more robust teeth with inflated cusps and stronger lophs and a calcaneus with extra articulation for the astragalus and navicular. The new species is stratigraphically well constrained and probably represents the youngest known species of the genus, extending its geological record into the Middle Eocene. It also shows that mimotonids coexisted for millions of years as a side branch of duplicidentates with the earliest stem lagomorphs, including Dawsonolagus.

Highlights

Glires consists of two modern groups: rodents and lagomorphs
The age of G. ellae is poorly constrained, but this species probably dates to the late Early Eocene (Kraatz et al, 2009), younger than G. elkema
The m3 differs from ml and m2 in having a longer talonid and a more pronounced hypoconulid. Compared to those of G. elkema and G. ellae, the talonid of G. shevyrevae is relatively shorter and the hypoconulid is reduced; it does not form a projection at the posterior end of the tooth

Summary

INTRODUCTION

Glires consists of two modern groups: rodents and lagomorphs. the monophyly of Glires has been a matter of debate, recent morphological and molecular evidence strongly supports the recognition of Glires as a clade (Meng and Wyss, 2001; Huchon et al, 2002; Meng et al, 2003; Douzery and Huchon, 2004; Asher et al, 2005; Bininda-Emonds et al., 2007). Duplicidentata is defined as all members of Glires sharing a more recent common ancestor with Lagomorpha than with Rodentia (Meng and Wyss, 2005). Gomphos has been shown to be a late-branching mimotonid and the sister group of Lagomorpha based on morphological evidence (Meng et al, 2003, 2004; Asher et al, 2005). The initial species identification was based on a fragmen¬ tary lower jaw, which was first named by Shevyreva (Shevyreva et al, 1975) and rede¬ scribed by Zhegallo and Shevyreva (1976) and by Dashzeveg and Russell (1988) This specimen was from members II and III of the Gashato (Khashat) Formation at the Ulan-Nur Basin (Dashzeveg, 1988). The age of G. ellae is poorly constrained, but this species probably dates to the late Early Eocene (Kraatz et al, 2009), younger than G. elkema

MATERIALS AND METHODS

DISCUSSION