Dictionary of Human Evolution and Biology

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Family of archaic fossil mammals belonging to the order Plesiadapiformes. Vernacular microsysopid. Known from the late Paleocene to late Eocene of North America and Europe; nine genera of forms ranging from 20g to almost 3 kg. Considered to be closely related to the Palaechthonidae and some authors include that family within the Microsyopidae. Dental formula, maxilla:; mandibular dental formula variable; family characterized by a caniniform upper incisor and lanceolate lower central incisors. The dentition resembles that of other plesiadapiforms and the cranial arterial system resembles that of extant primates, but the structure of the ear (e.g. nonpetrosal auditory bulla) is insectivore-like and some authors think that this group should be included in order Insectivora. Diverse group in which diet ranged from insectivory to plant material.