Anterior Dentition of Notharctus and the Adapid-Anthropoid Hypothesis

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Abstract
We describe the morphology of the first complete incisor-canine complex for Notharctus tenebrosus. Gregory’s classic description, based on heavily reconstructed and fragmentary material, needs to be amended to include the following points: I1 occludes simultaneously with I1–2; I2 is essentially nonocclusal and staggered behind I1; RI1 and LI1 do not contact interstitially but are separated by a small median diastema; I1 bears a prominent mesial prong. These five features are distinctly lemuriform in appearance: in general Notharctus is phenetically most similar to the pattern found in some lemurids and indriids. We consider an abstraction of the common plesiadapiform-omomyid anterior dental configuration as the primitive primate character state and argue that the adapid (sensu lato) morphology is derived. We further suggest that this predominantly Eocene group is the sister taxon of modern lemuriforms. The incisor-canine morphology of Adapts and Leptadapis is autopomorphic and less suggestive of the primitive pretoothcomb strepsirhine dentition than the notharctine pattern appears to be. While the morphologically simple lower incisors of notharctines are truly similar to those of anthropoids, the preponderance of anatomical differences within the incisor-canine complex leads us to conclude that these similarities were convergently evolved in adapids and the higher primates. The least refuted hypothesis of anthropoid origins, and the one which appears to make most phenetic as well as cladistic sense, acknowledges the monophyly of the Haplorhini and the likelihood that anthropoids are descendants of an early tarsiiform stock.