61st Annual Report on Research 2016

The WU-26 (Washington University vertebrate locality #26) micro-mammal locality provides a unique glimpse into the mammal community which inhabited the Uinta Basin about 40 million years ago during middle Eocene time. WU-26 is the first micro-mammal community from the upper Uinta Formation. Stratigraphically WU-26 lies approximately 40m below the base of the Brennan Basin Member of the Duchesne River Formation. Uinta Formation mammals define the Uintan North American Land Mammal age. Ongoing results of our excavations indicate that several mammal species thought to have gone extinct at the end of Uinta B time actually continued to inhabit the Uinta Basin throughout the deposition of the Uinta C Member. This includes a diverse suite of four to five genera of Omomyid primates (Westgate & Townsend, 2016).

In 2015, our field crew collected samples from the 15 cm thick vertebrate fossil–bearing stratum at WU-26 in an order to get a larger and more diverse fauna. The crew excavated about 3900 kg (4.3 tons) of bulk sample from WU-26. After concentrating the samples by locally screen-washing them twice in the Green River, we trucked the resulting 135 kg (300 lbs.) of concentrate to the Lamar University Paleontology Lab. By soaking the concentrate in naptha, and then water, and re-screen-washing, each was then further reduced to a about 14 kg (30 lbs.) of bone and tooth-rich sample. It was then sorted by size using Standard screens and prepped for specimen discovery. Mammalian fossils were identified to genus and or species. Through this process in the fall of 2015 and spring of 2016 we increased the sample size of identifiable mammal specimens from WU-26 by more than 200 specimens. The sample size currently exceeds 700. The more common taxa are beginning to be represented by statistically significant sample sizes. The undergraduate student researchers presented the results of the 2015 field season at the 2015 annual student research conference of Sigma Xi in Kansas City, MO.

In the summer of 2016, our field crew collected bulk samples from WU-26 ('The Pond' locality) to increase the size and diversity of the known fauna. Our crew excavated about 4500+ kg (5 tons) of bulk sample. Since 2007, we have removed approximately 30,000 kg (33 tons) of bulk sample from the 15 cm (6 inch) thick vertebrate-bearing horizon at 'The Pond locality.' After concentrating the samples by screen-washing in the Green River, we trucked the 110 kg (250 lbs.) of concentrate to the Lamar University Paleontology Lab. The same lab techniques used to concentrate samples in the fall of 2015 will be used in fall 2016. This coming fall & spring we expect to increase the sample size of identifiable mammal specimens by up to 200 teeth.

We also collected samples for pollen analysis. These were processed by a commercial lab in Alberta, Canada and forwarded to Dr. Carole Gee, a fossil pollen expert at the University of Bonn, Germany. Although the pollen, spores and dinoflagellate fossils identified by Dr. Gee constitute a small floral community, it is the first one to be recovered from the Uinta Formation, and will enhance attempts at paleoecologic analyses, which in the past have been primarily based on mammalian remains.

In addition, by collaborating with Drs. Howard Hutchison and Pat Holroyd (University of California-Berkeley Museum of Paleontology), we have also begun a paleoecological analysis using the fossil community of aquatic and terrestrial turtles preserved at WU-26. The presence of the carretochelyid Pseudanosteira pulchra and other associated turtle genera, suggest that climatic conditions during deposition of Uinta C were subtropical to tropical and warmer than that suggested by past researchers (Westgate & Townsend, 2016).

Field activities have provided students with first hand experiences in fossil excavation, stratigraphic analysis and primitive camping techniques. Laboratory time has provided experiences in sample processing techniques, how to use binocular microscopes for extended periods, as well as specimen analysis techniques and specimen curation. Research presentations at scientific conferences has provided experiences in developing poster presentations, as well as verbal presentation skills, and enhanced students' vitas with publications.

New discoveries of taxa thought to have gone extinct at the end of Uinta B time will have an impact by correcting previously erroneous interpretations of significant climate change during the Uinta B to C transition. They will also correct false interpretations of a sharp reduction in Omomyid primate diversity in the Uinta Basin during Uinta C time.

Westgate, James & Beth Townsend. 2016. A comparison of two late Uintan (late middle Eocene) micro-mammal faunas from the Central Rocky Mountains and Texas Coastal Plain & their paleoecologic implications. Society of Vertebrate Paleontology 76th meeting Salt Lake City, Program & Abstracts, p. 248.