Cladogenesis and replacement in the fossil record of Microsyopidae (?Primates) from the southern Bighorn Basin, Wyoming.

The early Eocene of the southern Bighorn Basin, Wyoming, is notable for its nearly continuous record of mammalian fossils. Microsyopinae (?Primates) is one of several lineages that shows evidence of evolutionary change associated with an interval referred to as Biohorizon A. is replaced by a larger species, , during the biohorizon interval in what is likely an immigration/emigration or immigration/local extinction event. The latter is then superseded by after the end of the Biohorizon A interval. Although this pattern has been understood for some time, denser sampling has led to the identification of a specimen intermediate in morphology between and , located stratigraphically as the latter is appearing. Because specimens of have been recovered approximately 60 m above the appearance of , it is clear that did not suffer pseudoextinction. Instead, evidence suggests that branched off from a population of , but the latter species persisted. This represents possible evidence of cladogenesis, which has rarely been directly documented in the fossil record. The improved understanding of both evolutionary transitions with better sampling highlights the problem of interpreting gaps in the fossil record as punctuations.