Dictionary of Human Evolution and Biology

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Plesiadapis Gervais, 1877

Best known mammal of the family Plesiadapidae from the late Paleocene and early Eocene of Europe and the Rocky Mountain region of North America; contains from 13 to 15 species. This animal, previously considered if not a basal primate then closely related to whatever gave rise to the primate line, provides a model for what primate evolutionary biologists believe the niche of the earliest primates would have been; it may have evolved from the earlier Pronothodectes. Plesiadapis species were arboreal quadrupeds with short, but stout, legs, long claws, and a bushy tail (the impression of which was preserved in limestone). Dental formula uncertain: 2.0.3.3 or 1.0.2-3.3; the number of lower premolars reduced over time; some species (e.g. P. anceps) may have retained canines; the dentition is suggestive of adaptations for plant eating; the dental formula precludes any Plesiadapis species as an ancestor for any of the earliest known primates of the Eocene. Another unprimate trait is the development of the auditory bulla from entotympanic bone rather than from petrosal bone. Estimated body mass for the Plesiadapis species ranged between 300 and 1750 g.

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