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INTRODUCTION
Plesiadapid cranial material has been previously described as sharing a number of
features with crania of the Carpolestidae, the proposed sister taxon of the Plesiadapidae
(Bloch and Silcox, 2006; Bloch et al., 2007). However, these taxa also exhibit a number
of cranial morphological differences. Some of these differences appear to be the result of
plesiadapid autapomorphies, while others appear to reflect carpolestid autapomorphies.
Features currently thought to be shared by and to reflect a close relationship
between plesiadapids, carpolestids, and in some cases (features 1-2 below) anatomically
modern primates (see Chapter 1: Fig. 1.1) (= Euprimates: Hoffstetter, 1977), include the
following: (1) a petrosally derived tympanic bulla, (2) a posterior carotid foramen with a
posteromedial position, (3) a separate foramen rotundum and superior orbital fissure, (4)
orbital contact between the maxilla and frontal bones in the orbital cavity and (5) a nasal
bone that becomes mediolaterally narrow at its caudal extent where it contacts the frontal
bone (Bloch and Silcox, 2006; Bloch et al., 2007). On the other hand, some major cranial
features of plesadapids that currently appear to separate them from the Carpolestidae
include the following: (1) premaxillae that contact the frontal bones, (2) an external
auditory meatus that is expanded into a tube-like form and (3) an internal carotid artery
with non-functional stapedial, promontorial and main stem branches.
If the cladistic hypothesis that plesiadapids and carpolestids are sister taxa is
correct, basal plesiadapids may lack some of the autapomorphies separating more derived
members of the group from the Carpolestidae. Furthermore, basal plesiadapids should
retain synapomorphies apparently shared by carpolestids and more derived plesiadapids.
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