A pantodont (Mammalia) from the latest Puercan North American Land Mammal Age (earliest Paleocene) of the Western Interior, USA

Abstract

Discovery of an Alcidedorbignya-like isolated upper molar in an early Paleocene (latest Puercan, Puercan 3, North American Land Mammal Age) local fauna found in the Tullock Member of the Fort Union Formation in northeastern Montana has been cited in the paleontological literature. This fossil is described, and a new genus and species, Crustulus fontanus, are established. They add to the taxonomic diversity of Puercan 3 local faunas in the North America Western Interior. The tooth’s morphology including a deep ectoflexus, nearly parallel preparacrista and postmetacrista, and expansion of the postcingulum, suggests evolution to accommodate increased herbivory. The appearance of C. fontanus with no clearly related taxa in older Puercan or Lancian (latest Cretaceous) local faunas of the currently sampled areas of the Western Interior indicates it probably was yet another post-Cretaceous/Paleogene boundary immigrant into this region. The few characters preserved in the single upper molar strongly suggest but do not conclusively indicate phylogenetic affinities with pantodonts. Perhaps C. fontanus was a member of yet another lineage stemming from the common ancestry of pantodonts and tillodonts. It is the oldest record of this complex group in North America.

http://www.zoobank.org/urn:lsid:zoobank.org:act:3643EA78-9A1A-4A2A-BFAF-4C2B6355B834

Keywords:

• Pantodonta
• early Paleocene
• Puercan
• Tullock
• Montana

Acknowledgements

I thank Gregg Gunnell, Jerry Hooker, and David Polly for the opportunity to contribute to this volume honoring Percy Butler, a long-time friend and mentor. In my experience, Percy always enjoyed a good puzzle and here is one. I wish I had his thoughts and insights on the nature and affinities of Crustulus fontanus. Thanks for their efforts in field and laboratory work are due to the late Harley Garbani and many students and staff of the University of California Museum of Paleontology. Lester and Robert Engdahl gave us access to the Biscuit Springs locality and supported our field work. The Bureau of Land Management provided the necessary permits for our field work, thank you. The scientific illustrations of UCMP 136524 (Figure 2) are the work of Kathy Sanders and were formatted by Gabriel-Paul Santos. The photographic image of the tooth (Figure 3) was taken by David Strauss. I greatly appreciate their contributions to this study. Also, I am indebted to Wang Yuan-qing, Christian de Muizon, Patricia Holroyd, Brian Rankin, and Gregory Wilson for exchanges of information and/or discussions through the course of development of the research reported here. Gregg Gunnell, Jerry Hooker, and Christian de Muizon provided very helpful reviews of the initial manuscript. This is University of California Museum of Paleontology contribution number 2079.