Bighorn Basin, Wyoming

The Bighorn Basin of northern Wyoming is a geologist's paradise, with fossil-bearing sediments of nearly all ages from the Cambrian to the Oligocene. Older sediments are found along the margins of the basin and in the beautiful mountains that flank the basin (the Bighorns, Pryors, Beartooths, and Absarokas). Particularly important are the extensive exposures of Paleocene and Eocene age that cover the center of the basin, which are among the most fossiliferous continental beds of this age in the world.

For the last 25 years we have conducted field work during the summer in the seemingly inexhaustible early Eocene Willwood Formation in the southern Bighorn Basin (for many years in association with Tom Bown of the USGS). During that time we have established more than 1000 fossil localities from throughout the 700 meter-thick section that spans almost 3 million years(about 55.5 to 52.7 my ago). Our collection of more than 50,000 fossil mammals and other vertebrate fossils is catalogued at the Smithsonian Natural History Museum, though much of it is housed in the Center for FAE to facilitate study. Included are about 200 species of fossil mammals, including some of the largest available samples of the earliest primates, ungulates, carnivores, and rodents.

Research focuses on several aspects of these fossils: comparative and functional anatomy, tempo and mode of evolution, systematics and relationships, origins of mammalian orders, and faunal composition and turnover. Since many early Eocene mammals were long known only or primarily from their teeth, special effort has been directed toward finding and restoring their postcranial skeletons. Study of postcranial anatomy provides clues to locomotor and associated behaviors, as well as relationships. We have collected hundreds of partial skeletons, including the oldest known skeletons of primates, artiodactyls, and carnivores. The stratigraphic density and richness of our samples makes them particularly important for addressing questions of evolutionary patterns, rates, and processes. Our research on evolving lineages of mammals has adduced evidence that many groups evolved gradually through the early Eocene in the Bighorn Basin. Amy Chew's recent dissertation analyzed the stratigraphic distribution of mammal species in our section and statistically demonstrated the existence of two episodes of faunal turnover during the early Eocene. Our current focus is on faunal composition in the earliest Eocene (Wa-0) immediately following the major turnover event at the Paleocene-Eocene boundary. We are also concentrating efforts on a quarry located at the top of biohorizon A (one of the other episodes of faunal turnover), which is producing the first evidence of the micro-mammal fauna during that episode. Some pertinent publications resulting from our Bighorn Basin research, besides those cited elsewhere on this webpage, are listed here.

Although we work hard during the week, often in temperatures that reach or exceed 120° in the sun, there's always time to relax around the campfire in the evening; and there are many opportunities for recreation on days off, including visiting museums in Cody or Thermopolis, hiking or relaxing in the mountains, or whitewater rafting through the Wind River Canyon. Yellowstone National Park is less than 3 hours away. We recently received new funding from NSF in support of this research and therefore expect to continue field work in the Bighorn Basin at least through 2008.

Basal Eocene (Wa-0) exposures northeast of Worland, Wyoming. We have concentrated on this area during the last four field seasons. These strata preserve a record of the oldest known true primates, artiodactyls, and perissodactyls, which immigrated into North America during the brief interval of global warming at the beginning of the Eocene.

The 2005 field crew: L to R in back row, Benjamin Schormann (University of Bonn, Germany), and visitors Prof. David Archibald (San Diego State) and his wife, Gloria Bader. Front row: Mercedes Gutierrez and Rachel Dunn (Washington University), FAE grad student Gina McKusick, recent FAE Ph.D. Amy Chew, and Dr. Rose.

Shawn Zack and Tonya Penkrot excavate a Wa-0 site in 2004.

Dr. Tom Bown guides us across a difficult drainage.

Gina McKusick and Mercedes Gutierrez prepare dinner in the field kitchen.

Gina and Mercedes quarrying at Jay's Pocket Quarry in the lower Willwood Formation, 2005.

Western India

Little is known of the early Cenozoic land mammal fauna of India, and until recently, nothing had been found from prior to the middle Eocene. Because India has been suggested as a possible source area of some of the groups that first appear in the early Eocene, it is critical to find evidence of Paleocene and early Eocene mammals there.

With that objective in mind, we began a collaboration in 2001 with Prof. Ashok Sahni (Panjab University, Chandigarh) and Prof. Rajendra Rana (Garhwal University, Srinagar) to explore continental sediments, especially lignites, in western India for land mammals. Work focused initially on western Rajasthan, and later on lignite mines in Gujarat. In 2004 Dr. Thierry Smith of the Royal Belgian Institute of Natural Sciences, Brussels, joined our team. These efforts have resulted in discovery of diverse assemblages of early Eocene fishes, sharks, a few reptiles, and in one area, mammals-the first early Eocene land mammals from India. Among more than a dozen species recovered so far are the oldest bats known from Asia. The work has been funded by the National Geographic Society.

In 2004 Dr. Thierry Smith of the Royal Belgian Institute of Natural Sciences, Brussels, joined our team. Our multinational team, including graduate students from FAE, the Royal Belgian Institute, and Garhwal University, worked at the Vastan Mine in February 2006. These efforts have resulted in discovery of diverse assemblages of early Eocene fishes, sharks, a few reptiles, and in one area, mammals-the first early Eocene land mammals from India. Among more than a dozen species recovered so far are the oldest bats known from Asia, as well as insectivores, primates, artiodactyls, and a probable basal tethythere, recently described in the Journal of Vertebrate Paleontology. The work has been funded by the National Geographic Society.

Resulting publications:

Sahni, A., R.S. Rana, R.S. Loyal, P.K. Saraswati, S.K. Mathur, K.D. Rose, S.K.M. Tripathi, and R. Garg. 2004. Western Margin Palaeocene-lower Eocene lignites: biostratigraphic and palaeoecological constraints. Proceedings 2nd Conference, Association Petroleum Geologists (Khajuraho, India), ONGC, Tech.Sess. III: 1-22.

Rana, R.S., H. Singh, A. Sahni, K.D. Rose, and P.K. Saraswati. 2005. Early Eocene chiropterans from a new mammalian assemblage (Vastan Lignite Mine, Gujarat, Western Peninsular Margin): oldest known bats from Asia. J. Palaeontological Soc. India 50(1): 93-100.

Rana, R.S., K. Kumar, H. Singh, and K.D. Rose. 2005. Lower vertebrates from the Late Palaeocene-Earliest Eocene Akli Formation, Giral Lignite Mine, Barmer District, western India. Current Science 89: 1606-1613.

Rana, R.S., K. Kumar, R.S. Loyal, A. Sahni, K.D. Rose, J. Mussell, H. Singh, and S.K. Kulshreshtha. 2006. Selachians from the early Eocene Kapurdi Formation (Fuller's Earth), Barmer District, Rajasthan, India. J. Geol. Soc. India 67: 509-522.

Rose, K.D., T. Smith, R.S. Rana, A. Sahni, H. Singh, P. Missiaen, and A. Folie. 2006. Early Eocene (Ypresian) continental vertebrate assemblage from India, with description of a new anthracobunid (Mammalia, Tethytheria). J. Vert. Paleont. 26: 219-225.

Searching for fossil vertebrates at Giral Lignite Mine near Barmer, Rajasthan. FAE graduate (then grad student) Jay Mussell at right.

Dr. Rose and Prof. Sahni at Giral Mine.

Drs. Rose, Loyal, and Rana on camels at the Sam Sand Dunes, western Rajasthan.

Dr. Rana sorts screen-washed sediment at Vastan Mine, Gujarat.

Vastan Lignite Mine, east of Surat, Gujarat, February 2006.

Rajasthani musicians near Sam, northwest of Barmer.

Screen-washing at Vastan Mine; FAE grad student Gina McKusick at right.

Our multinational team excavates the mammal-bearing layer at Vastan during February 2006.

Soft-shell (trionychid) turtle shell fragment in situ at the Vastan Mine, February 2006.

Local vegetable vendor in Gujarat, India.

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