Know Your Primate: Notharctus

Infraorder: Lemuriformes
Family: Adapidae
Subfamily: Notharctinae
Genera: Notharctus
Species: N. robinsoni, N. tenebrosus, N. pugnax, and N. robustior
Notharctus is an Eocene genera of primates found only in North America. Notharctus forms a single evolving lineage with the earlier Cantius and Pelycodus, consequently it can be hard to tell where Cantius leaves off and Notharctus begins.

Notharctus is similar in overall morphology to later lemuriformes such as Indri and Lemur. They have long hindlimbs and short forelimbs – indicating they were clingers and leapers. They have opposable thumbs and opposable big toes. Cranially, they have a fused mandibular symphysis – a trait that is used to divide Cantius from Notharctus – a small braincase, rather large sagittal and nuchal crests (with the temporal lines converging on the sagittal crest posterior to the coronal suture), a free tympanic ring and relatively small orbits (indicating a diurnal lifestyle). There are a number of fairly complete skeletons, unfortunately I have not been able to find pictures of them. Here is a good picture of the skull of N. tenebrosus
(picture from here
You can find four interesting articles on Notharctus here
You should also check out the Primate Fossil Database maintained by the University of Texas at Austin Anthropology Department. It is a phenomenal resource!