One extinct relative of primates that lived in North America about 60 million years ago is called Plesiadapis cookei. Dental characteristics of P. cookei were compared to those of other primate species in the article "Evidence of Dietary Differentiation among Late Paleocene-Early Eocene Plesiadapids" (American Journal of Physical Anthropology, Vol. 142, No. 2, pp. 194-210) by D. Boyer et al. The following table gives the dentary depth, in millimeters, for a sample of molars from the skulls of 18 P. cookei specimens.

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18.12 19.48 19.36 15.94 15.83 19.70 5.76 17.00 13.96 16.55 15.70 17.83 13.25 16.12 18.13 14.02 14.04 16.20