New Mexico Geological Society Annual Spring Meeting — Abstracts

The Puercan Land Mammal Age (Paleocene, earliest Danian; ~66-65 Ma) is the earliest North American faunal stage of the Cenozoic era, immediately after the end-Cretaceous (K-Pg) mass extinction event. It is typified by the adaptive radiation of eutherian mammals, including placentals, following the annihilation of the non-avian dinosaurs, which opened up numerous ecological niches. Unfortunately, the spatiotemporal scale of Puercan eutherian diversification remains elusive. Several authors have increased differentiation between “northern” and “southern” faunas in western North American, as was the case in vertebrate faunas below the K-Pg boundary; additionally, endemism is widely believed to have higher in the later Pu2 and Pu3 intervals compared to the earlier Pu1 interval. However, this is complicated by a number of Pu1 sites in a possible “transition zone” between northern and southern faunal provinces with many unusual endemics.

To resolve these issues, I gathered abundance data on all currently valid Puercan eutherian genera and species, based on a critical review of the published literature and of museum catalogs. Biogeographic and biostratigraphic trends within basins and intervals were tested using DCA, PCA, and NMDS analyses in R, as well as with agnes hierarchial dendrograms. Scatterplots of DCA and NMDS results – based on Bray-Curtis, Jaccard, and Kulczynski distance metrics – generally resolved Puercan eutherian localities along a north-south gradient, with “northern” sites from the Bighorn, Calgary, and Williston basins representing one endmember, “southern” sites from the Denver, Paradox and San Juan basins representing another, and sites from the Crazy Mountain, Great Divide, and Hanna basins representing the “transition zone” in between. These same scatterplots also demonstrate moderate distinction of the Pu1 interval from the combined Pu2/Pu3 intervals.

In agnes dendrograms based on Kulczynski distances, most sites were sorted into three well-supported clusters: a group of Pu1 “northern” sites, a group of Pu3 “northern” sites, and a group of Pu2/Pu3 “southern” sites. However, several Pu1/Pu2 northern and transition-zone sites (i.e. Alexander, Hiatt, Polecat Bench, MBHT Rav-W1) formed a fourth cluster more closely resembling the Pu2/Pu3 “southern” fauna. This supports the notion of increased faunal differentiation over the Puercan, as well as an early northward expansion of the Pu2/Pu3 southern faunal province at the expense of the Pu1 northern “disaster fauna”. Future studies will focus on the effect of site lithology and sampling techniques in these evaluations of Puercan eutherian biogeography and biostratigraphy.