Dictionary of Human Evolution and Biology

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Problematic fossil taxon known mainly from dentition and jaws that historically was included as either an infraorder or suborder among the primates by some and, more recently, placed outside the order Primates by others. As an order it contains ten families. This group is considered a wastebasket taxon by most researchers and contains more taxonomic diversity than that found among the living primates. Nevertheless, this group is considered by many workers to contain the best candidates for the primate progenitor, although it may also contain the ancestors of bats, tree shrews, and colugos. Plesiadapiforms were the most common mammals in many of the known Paleocene faunas, especially in North America. The primitive dental formula is, but later members show reduced dentition and many members developed specialized dentition. The primitive dental formula precludes the plesiadapiforms as ancestors of the earliest prosimians, which have four premolars; another unprimate-like characteristic is that the auditory bulla does not appear to be derived from the petrosal region of the temporal bone.

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