New Mexico Geological Society Annual Spring Meeting
April 13, 2018

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The Beginning of the Age of Mammals in New Mexico: New Insights on the Rise of Placentalia Based on a Preliminary Comprehensive Phylogeny

Thomas E. Williamson1, Stephen L. Brusatte2, Jan E. Janecka3, Sarah L. Shelley4, Michelle Spaulding5 and John R. Wible4

1New Mexico Museum of Natural History and Science, 1801 Mountain Road, NW, Albuquerque, NM, 87121,
2University of Edinburgh, School of GeoSciences, Edinburgh, Scotland, United Kingdom
3Duquesne University, Department of Biological Sciences, Pittsburgh, PA
4Carnegie Museum of Natural History, Pittsburgh, PA
5Purdue University, Northwest, Department of Biology, Westville, IN

The Cenozoic radiation of mammals was a profound moment in vertebrate evolution, however, many aspects of this radiation remain poorly understood, largely because phylogenetic and macroevolutionary studies have ignored mammals from the Paleocene. In order to address this deficit, we are building a comprehensive higher-level phylogeny using anatomical and genetic data of a large number of mammalian taxa (both extinct and extant). This phylogeny will include an unprecedented number of Paleocene taxa, including many enigmatic forms that have formerly been relegated to “wastebasket” groups.

This project will incorporate a wealth of fossil specimens that have been collected from the Paleocene Nacimiento Formation of the San Juan Basin, northwestern New Mexico. The Nacimiento Formation contains the longest and most complete record of mammalian succession through the early Paleocene. Moreover, many extraordinary specimens have been amassed from these deposits, especially over the last 2-3 decades, through focused collecting efforts by the New Mexico Museum of Natural History and Science. These fossils are being studied using a variety of new techniques, including high-resolution CT scanning, that are revealing new details of the anatomy and functional morphology, that are bringing new insights into the biology and evolution of these archaic animals.

Preliminary results of our comprehensive phylogeny of Paleocene mammals build upon previous large datasets, including most Paleocene lineages – (262 taxa [58 extant and 204 extinct]) scored for over 2,000 morphological characters. Molecular data from the extant taxa, over 35,000 base pairs from 26 nuclear genes will ultimately also be included. These results are based on use of maximum parsimony, but later analyses will also use maximum likelihood and Bayesian methodology. Our preliminary results find that most Paleocene taxa are found to be stem members of major extant clades (e.g., Primates, Afrotheria, Laurasiatheria, Carnivoramorpha, Euungulata). When coupled with high-resolution geochronological record being developed from the Nacimiento Formation record, our analyses show that many major mammalian clades originated very early in the Paleogene.


Paleocene, Paleogene, mammals, phylogeny, Nacimiento, San Juan Basin

pp. 79

2018 New Mexico Geological Society Annual Spring Meeting
April 13, 2018, Macey Center, New Mexico Tech campus, Socorro, NM