Characterization of Modern Turtle Death Sites for Comparison with Late Eocene and Early Oligocene Turtle Sites

Abstract

Taphonomic studies of extant turtles are useful for interpreting the taphonomy of fossil turtles. In order to provide modern comparators for fossil turtle sites, we have characterized two modern turtle (Chrysemys picta) deathsites; one in northwestern Nebraska and one in southwestern South Dakota. During these studies we characterized carapace position (up or down), presence or absence of non-shell elements, relative spatial position of the turtles and presence of shell disturbances (lesions). In the Trunk Butte site (Nebraska), six turtles were in carapace up position, five were in carapace down and one was not determinable. In addition, seven of those turtles contained some non-shell elements and five had indeterminable non-shell element status. At the Buffalo Gap site (South Dakota), four were carapace down, two were carapace up and three were not determinable for that character. Six of these had non-shell elements associated with them and three had no non-shell elements. The occurrence of turtles in the carapace down position suggests either the presence of medium to large scavengers able to overturn a turtle or that the turtle died while in the water and overturned while sinking. The spatial distributions of turtles in the two modern sites were also plotted and compared to that of two Whitney (Brule Formation, White River Group) and one Chadron (White River Group) site to address the hypothesis that the fossil assemblages were associated with small ponds. The results suggest that the fossil turtle sites were not the result of death events associated with small ponds, nullifying that hypothesis.