Abstract

The relationships of the extinct mammalian family Apatemyidae are poorly resolved. Three new, well-preserved crania of Labidolemur kayi from the late Paleocene (Clarkforkian) and early Eocene (Wasatchian) of North America are described in part using ultra high resolution X-ray computed tomography data. These specimens permit the first descriptions of critical components of apatemyid cranial anatomy, such as the composition of the tympanic roof, and the pathways of the internal carotid artery and facial nerve. Results from cladistic analyses of morphological data for known apatemyids and a broad sample of eutherians suggest that apatemyids are basal members of Euarchontoglires, with weak support for a sister-group relationship with Glires. Although apatemyids are sufficiently different from other mammals to be placed in their own order, Apatotheria, it is clear that they are likely to be important for understanding primitive characteristics of Euarchontoglires and Boreoeutheria.