TRACES OF RECENT AND ANCIENT SEA TURTLE NESTING

Nesting traces of modern and ancient sea turtles have been described, but not well documented in the literature. Study of Recent nesting loggerhead sea turtles on St. Catherines Island, Georgia, provides a model for the suite of sedimentary structures produced by nesting sea turtles, and an analog for trace fossils in ancient near-shore marine sedimentary rocks. The suite of nesting structures includes: (1) large crawlways produced by mature female turtles; (2) smaller scale crawlways made by hatchlings; (3) distinctive disrupted sediments of the nest and (4) depredated nests. Nest types described on St. Catherines Island include simple and complex, unobstructed and obstructed nests, situated in backbeach, dune, washover fan, and forebeach habitats. Nests consist of disrupted elliptical surface layers filling a broad, shallow covering pit approximately 20 - 30 cm deep, overlying a smaller body pit, and both overlying a vertical-walled, urn-shaped egg chamber. Loggerhead nests average 2.38 m long and 1.96 m wide; egg chambers average 20 cm in diameter and extend approximately 30 cm into the substrate beneath the bioturbated sand filling the body pit, for a total average depth of 54.90 cm. Subsequent erosional, depositional, or predatory events may modify or obliterate the sediments and entrained nest structures, making them easy to overlook or misinterpret if seen in the fossil record. Fossilized nesting structures are described from the Fox Hills Sandstone of Colorado, including two egg chambers, a body pit, a crawlway, and associated backbeach sedimentary structures.