Rare Mammal Fossil Discovered in Wyoming

A fossil discovered near Kemmerer, Wyoming, may be the first of its kind and is the largest mammal found to date in the 50-million-year-old Green River Formation. The discovery of this ancient tapiromorph may support a North American origin of tapirs that in modern times typically inhabit jungles and forests in South and Central America and Southeastern Asia.

Due to its potential significance, the specimen is being prepared for scientific purposes. “Properly preparing the specimen with special attention to keeping soft tissue fossilization intact is important for future research,” says Andrea Loveland, geologist at the Wyoming State Geological Survey (WSGS).

Rick Hebdon, owner of Warfield Fossil Quarries, collected the fossil in summer 2016 from the Fossil Butte Member of the Green River Formation. The specimen was found in several pieces and damaged by weathering and roots. The majority of the animal’s teeth are missing, and its skull is damaged.

The fossil was first identified as Heptodon calciculus by the late Dr. Gregg Gunnell, paleontologist and former director of the Duke (University) Lemur Center. Gunnell’s initial identification comes with a few caveats, as some characteristics of the specimen deviate from what is typical of a standard Heptodon. The specimen may be an early occurrence of Hyrachyus or Helaletes, both tapiromorphs that more closely align with rhinoceroses and true tapirs, respectively. The specimen may also be a new genus of ceratomorph or tapiroid.

“My understanding is that this is definitely the first occurrence of this fossil in the Green River Formation and, depending on which of the three identifications listed above is correct, could be the first of its kind ever. More work on this specimen is needed after it has been prepared,” says Dr. Mark Clementz of the University of Wyoming Department of Geology and Geophysics.

Researcher Mike Eklund will prepare the specimen under a microscope with time-lapse photography. Still photography under different angles of visible light and ultraviolet light will help detect detail and soft tissue fossilization.

Prior to starting the preparation process, the rock slabs were CT scanned and X-rayed at Ivinson Memorial Hospital in Laramie, Wyoming, so that geologists could view and identify fossilized material encased in the rock. Stitches Acute Care Center, also in Laramie, conducted X-rays on a fourth large rock slab and several smaller pieces.

The specimen was found on a state-leased quarry and surrendered to state custody due to its distinction as a rare specimen per the Office of State Lands and Investments fossil permit regulations. After the preparation process is complete, the fossil will be housed at the WSGS and available for scientific research and display at museums. The WSGS serves as a repository for state-owned fossils.

"We are following the preparation of the fossil with great interest,” says WSGS Director, Dr. Erin Campbell. “This fossil has potential to be a significant scientific find, and we applaud Mr. Hebdon for bringing this state treasure to our attention.”

The fossil is being prepared at the recommendation of the Fossil Advisory Board, which advises the State Geologist/WSGS Director on specimens turned over to the State of Wyoming. Members of the Fossil Advisory Board are Seth Wittke and Andrea Loveland (WSGS), Mark Clementz and Laura Vietti (University of Wyoming Department of Geology and Geophysics), J.P. Cavigelli (Tate Geological Museum), and Kelli Trujillo (Uinta Paleo).

“The discovery of the Green River Formation fossil is exciting for the state of Wyoming,” says Vietti. “Not only is it an important fossil discovery for science, it also represents a unique collaboration between private collectors, Wyoming agencies, and the University of Wyoming.”

The public can learn more about the fossil and follow progress of its preparation on the WSGS’ website. Also, look for weekly updates on the agency’s Facebook, Twitter, and Instagram pages.