60th Annual Report on Research 2015

The WU-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.

In 2014, our field crew collected samples from WU-26 and two nearby localities in an attempt to get a larger and more diverse fauna. The crew excavated 1350 kg of bulk sample from WU-26. We also collected 900 kg from the newly discovered H2 locality and 100 kg from WU-2, both sites are high in the Uinta B Member in Uintah County, Utah. After concentrating the samples by locally screen-washing them in the Green River, we trucked the 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 few kilograms 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 2014 and spring of 2015 we increased the sample size of identifiable mammal specimens from WU-26 by more than 100 specimens. The sample size currently exceeds 500. The more common taxa are beginning to be represented by statistically significant sample sizes. H2 locality fossils were limited to remains of Lepisosteus sp. (gar) and Amia sp. (bowfin). The small sample from WU-2 yielded several mammal teeth including a cf. Mytonius sp. (tarsier-like primate) upper molar, which suggests that it should be more intensively sampled. The student researchers presented the results of the 2014 field season at the 2015 annual meeting of the Texas Academy of Science in San Antonio.

In a side study, some of our WU-26 bones were discovered to be enriched in uranium and are radioactive. They were included in a suite of radioactive bones ranging in age from early Eocene to Pleistocene in which gamma ray spectroscopy is being used to calculate the age of the specimens based on diminishing amounts of radioactive daughter products. Progress reports on this study were presented at the annual Geologic Society of America conference in Vancouver, Canada in October, 2014 and at the Society of Vertebrate Paleontology annual conference in Berlin, Germany in November, 2014.

In the summer of 2015, 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 3900 kg (4.3 tons) of bulk sample. After concentrating the samples by screen-washing in the Green River, we trucked the concentrate to the Lamar University Paleontology Lab. The same lab techniques used to concentrate samples in the fall of 2014 will be used in fall 2015. This fall & spring we expect to increase the sample size of identifiable mammal specimens by up to 200 teeth. Student field and lab assistants have successfully submitted an abstract and they will present the results of the 2015 field season at the annual Sigma Xi Student Research Conference in Kansas City, MO in October, 2015.

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.