Preliminary Results of Possible in Situ Turtle Eggs in the Kaiparowits Formation, Grand Staircase-Escalante National Monument, Utah

FERGUSON, Ashley L.; Idaho State University, Pocatello, ID

Abstract 

The Upper Cretaceous continental deposits recorded by the Kaiparowits Formation are richly fossiliferous in amniotes, including turtles, crocodilians, lizards, and many dinosaur species. However, to date, very little has been published or presented on fossil eggs in these deposits. Currently, the only eggs that have been described and published from the Kaiparowits belong to a gravid Adocus. Here, I present evidence of in situ partial eggs tentatively identified as turtle. The eggshell was found in 2017 in the informal middle unit of the Kaiparowits Formation within a green mudstone. The gastropods Lioplacodes and Viviparus are common in the mudstone and a theropod tooth was also found in association with the eggshell. The eggshell fragments were spread over an area of three-square meters. At least seven eggs have been identified, with more yet to be prepped. Exposed partial eggs indicate that the eggs likely have a spherical morphology of approximately 3-4 cm in diameter. The eggshell is extremely porous, suggesting incubation by burial, and lacks surface ornamentation. The curvature, porosity, and lack of surface ornamentation of the egg is typical of turtle eggs. Counts of the eggshell fragments produce a ratio of 61:39 concave up to concave down eggshell, consistent with in situ preservation. Future work will include scanning electron microscopy, computed tomography, thin sections, and further preparation of the specimens to identify the ootaxa, verify the taxonomic identification, and describe the taphonomy of the site in more detail.

Funding for this work is provided by the Bureau of Land Management No. L17AC00095 to Leif Tapanila.