INTRODUCTION

Oxyaenidae is one of the families included in the diphyletic order "Creodonta", with the Hyaenodontidae. Oxyaenidae represent the largest specialized carnivorous mammals from the Early and Middle Eocene, whereas Mesonychidae represent the largest non-specialized carnivorous mammals. They were distinctly larger and possessed a more specialized shearing dentition than the hyaenodontids. Four subfamilies are known: Tytthaeninae, the most primitive group; Ambloctoninae (= Palaeonictinae) characterized by a reduced M₂ and broad premolars; Oxyaeninae characterized by a large and bladelike M₂; and the hypercarnivorous Machaeroidinae characterized by a very bladelike M₂ and long upper canines protected by a ventral flange at the front of the jaw (Gunnell 1998). However, the placement of Machaeroidinae is presently uncertain, because they may belong to Oxyaenidae or to Hyaenodontidae. The group appeared in North America during the Late Paleocene (Gingerich 1980). Its diversification occurred mainly on this continent. It disappeared from North America during the Middle Eocene. Oxyaenidae appeared in Europe right after the Paleocene/Eocene transition (Smith and Smith 2001), and they disappeared rapidly there. Only oxyaenines and paleonictines are known in Europe. The Oxyaenidae are poorly known in Europe because they are rare and represented by very poor material (Rich 1971; Gunnell and Gingerich 1991).

The fossil locality of Le Quesnoy (Oise, Early Eocene, MP7) is located in the Paris Basin (Nel et al. 1999). This fossiliferous locality, located near Houdancourt (Creil area) (Figure 1), is one of the richest known for the Early Eocene of Europe. It provides information concerning the environment, the flora and the arthropod and vertebrate fauna and is important for the understanding of the mammalian fauna of the earliest Eocene in Europe. Nel et al. (1999) have already identified 24 species of mammals representing 20 families. The mammalian fauna appears well diversified and is similar to the Dormaal assemblage. The faunas share some taxa (e.g., Teilhardina aff. belgica, Landenodon sp., Paschatherium sp.), but differences do exist. The large species are better represented in Le Quesnoy, which is less biased taphonomically.

Thanks to this locality, our knowledge of the earliest Oxyaenidae is greatly increased. Nearly complete dentitions of oxyaenids are known from Le Quesnoy, allowing a new look at the fossils of Oxyaenidae previously discovered in Europe (Van Valen 1965; Rich 1971; Hooker 1998) and to a discussion of the evolution of this group in Europe.

Abbreviations

AMNH: American Museum of Natural History, New York

ARP: Argiles à lignites du Soissonnais, collection of the MNHN

BMNH: British Museum of Natural History, London

IRSNB M: Mammals, collection of types and figured specimens of the IRSNB

IRSNB: Institut Royal des Sciences Naturelles de Belgique, Bruxelles

MNHN: Muséum National d'Histoire Naturelle, Paris

QNY1 and QNY2: Le Quesnoy, collections of the MNHN

UM: University of Michigan, Ann Arbor

UCMP: University of California, Museum of Paleontology, Berkeley

YPM-PU: Princeton collection at Yale Peabody Museum, New Haven
M: mean, and OR: observed range; L: Length and W: Width

R: right; L: left