PRELIMINARY STUDY OF FRESHWATER GASTROPODS IN THE WAHWEAP FORMATION, BRYCE CANYON NATIONAL PARK, UTAH

Upper Cretaceous freshwater gastropods do not have an extensive literature. This lack of literature suggests that either they are not common or interest in their study is lacking. During a paleontological inventory of the Upper Cretaceous age sediments near Horse Hollow at the southern extremity of Bryce Canyon National Park (Utah), a large number of freshwater gastropods were observed. The gastropods were weathered-out of a 0.3 m-thick layer of chippy, tan siltstone overlying a gray mudstone that forms a ridge eroded into the Wahweap Formation. A 25 kg sample of fresh material was collected, screen-washed, and picked. This sample yielded more than 1,900 gastropod specimens. Associated with these gastropods were amiid vertebrae, crocodilian teeth, hadrosaurian tooth, and assorted bone fragments.

Small, high-spired forms dominate this population of freshwater gastropods. Size ranges from 1.90 mm in width and 2.60 mm in height to 20.0 mm in width and 32.0 mm in height. Preservation is moderate to poor with many apices and most apertural openings missing. Complete shells are scarce, but steinkerns are abundant. Sorting of the picked sample yielded at least twelve species in four genera. The four most likely genera are; Vivipara, Reesidella, Mesocochliopa, and incertae sedis.