Hatching

1. Covering Pits • Once the egg chamber is back-filled, the turtle enters a covering behavior characterized by front flipper sweeps (Hailman and Elowson, 19xx) pushing and throwing sand backwards and propelling the turtle forward. As the turtle moves forward with successive flipper sweeps, she almost always rotates 180 degrees either clockwise of counterclockwise and then exits the covering pit to crawl back to the ocean. The resultant sedimentary structure is a thin bioturbated layer (20-30 cm thick) covering the egg chamber and body pit .The structure exhibits an elliptical shape approximately 3.0 m long and 1.5 m wide bounded by flipper scarps, with an uneven surface, trails of loose, thrown sand, connected to entrance and exit crawlways. The covering pit and crawlways are exceedingly ephemeral structures on the surface, rapidly erased by wind, rain, and tides. ACKNOWLEDGMENTS This research has been generously supported by The Georgia Eisenhower Higher Education Program (now Improving Teacher Quality), The St. Catherines Island Foundation, Inc., The Turner Foundation, The JST Foundation, The Georgia Department of Natural Resources, Georgia Southern University, and the Museum of Geology and Paleontology, South Dakota School of Miners and Technology. The Limon, CO map is provided by Radar Acquisitions and the Cretaceous paleogeographis map is from USGS Professional Paper 1561. Loggerhead covering pit on top of a dune; McQueens Inlet, South Beach, St. Catherines Island.. Loggerhead body and covering pit on washover fan (a sand angel); Seaside Spit, North Beach, St. Catherines Island, Georgia. Scale = 10 cm. Loggerhead during flipper sweep in covering behavior. Hatching After approximately sixty days of incubation in the solar-heated sand, the eggs will hatch and the hatchling turtles will emerge from their egg shell. The hatchlings begin to dig themselves out by a crawling motion of flippers, loosening the sand around and above them which falls through the mass of hatchlings under the influence of gravity, often forming a "stope" or air chamber above the mass of wiggling little turtles. This mining activity continues as long as the hatchlings are in cool sand beneath the surface. When they near the surface with its solar-heated hot sand, the hatchlings stop their activity and become lethargic, until the sand cools during the night when activity is renewed and the hatchlings emerge from their nest and scamper toward the sea, forming hatchling crawlways. Near the surface the sand is dry and not cohesive, so the surface layer may fall into the stope forming a surface "dimple" announcing a imminent emergence. The final emergence often is en masse, although multiple emerges on successive nights is the norm. Synchronous emergence of large numbers of hatchlings often forms an emergence crater as the surface sand collapses into the void left by the hatchlings. Upon emergence at night the hatchlings head to the sea (downhill, away from the island silhouette, and toward the light and noise of the sea) forming a pie-shaped arc of anatomizing crawlways broadening the sea. Reading these crawlways often allows the documentation of interactions with predators on the beach and an estimate of the number of emergent hatchlings. These are exceedingly ephemeral traces easily destroyed by wind, rain, and tide. Table 1: Potential traces of sea turtle nesting and documentation (in red) of identified structures in Fox Hills Sandstone, elbert County, Colorado. Loggerhead hatchlings during a rare daytime emergence. Loggerhead hatchling crawling across the beach. Loggerhead hatchling crossing a heavy mineral sand. Up-side-down loggerhead hatchling producing an unusual trace as it tries to right itself on dune surface. Scale = 4 in (10 cm). The Fossil Record Because sea turtles nest in a dynamic environment with a low probability of preservation and their modern traces are largely unknown to most geologists and paleontologists, their ichnoloy still remains poorly known. However, by using modern sea turtle traces it is possible to predict what analogous trace fossils will look like when preserved in sedimentary rocks of Cretaceous to Holocene age. The abundance of body fossils of sea turtles attests to heir presence in many regions from Early Cretaceous to present; and indicates that they nested on sandy beaches in those regions during the same interval. Even though the preservation potential of back beach sediments is low, the very number of sea turtles and their multiple nesting behavior would be expected to produce a high potential for preservation where back beach sediments are preserved. This hypothesis was promulgated at the annual meeting of the Rocky Mountain Association of the Geological Society of America (Marsh and Bishop, 1986) by bringing modern loggerheadsedimentary nesting structures to the attention of western geologists who might have seen, or be expected to see, analogous fossil structures in the Cretaceous of the Western Interior. During a consult with E. I. DuPont on ghost Shrimp burrows Recent Analog cp ec bp cw ec Recent flipper marks in sea turtle crawlway (cw) in backbeach facies; South Beach, St. Catherines Island, Georgia. Scale = 10 cm. Collapsed Recent egg chamber in sea turtle nest (ec) in backbeach facies; South Beach, St. Catherines Island, Georgia. Scale = 10 cm. Trenched Recent sea turtle nest in backbeach facies; South Beach, St. Catherines Island, Georgia; showing covering pit (CP), Body pit (BP), and egg chamber (ec ). Scale = 10 cm. Fossil Example bp cw B C Fossilized sea turtle egg molds (arrow) in bottom of egg chamber; Fox Hills Sandstone Elbert County, Colorado. Hammer = 40 cm. Fossilized sea turtle body pit (bp) incised into backbeach facies; Fox Hills Sandstone Elbert County, Colorado. Scale = 10 cm. Fossilized flipper marks in sea turtle crawlway (cw) in backbeach facies; Fox Hills Sandstone Elbert County, Colorado. Scale = 10 cm. • Selected References • Bishop, G.A., N. B. Marsh, J. Barron, F. L. Pirkle, R. S. U. Smith. 1997. A Cretaceous sea turtle nest, Fox Hills Formation, Elbert Co., CO. Geological Society of America, Abstracts with Programs 29(6): A104. • Brannen, N. A., and G. A. Bishop. 1993. Nesting traces of the loggerhead sea turtle (Carettacaretta Linne), St. Catherines Island, Georgia: Implications for the fossil record. In K. M. Farrell, C. W. Hoffman, and V. J. Henry, JR. (eds.); Geomorphology and facies relationships of quarternary barrier island complexes near St. Marys, Georgia. Ga. Geol. Soc. Guidebooks 13(1): 30-36. • Frey, R. W. and S. G. Pemberton. 1987. The Psilonichnus ichnoconose, and its relationship to adjacent marine and nonmarine ichnocoenoses along the Georgia coast. Bull. Canadian Petrol. Geol. 35(3): 333-357. • Hailman, J. P. and A. M. Elowson. 1992.Ethogram of the nesting female loggerhead (Carettacaretta). Herpetologica 48(1): 1-30. • Radar Acquisitions. <http://www.radar.ab.ca/heavy_minerals.html>. • Roberts, L.N.R. and M.A. Kirschbaum. 1995. Paleogeography of the Late Cretaceous of the Western Interior of Middle North America---Coal Distribution and Sediment Accumulation. U.S. Geol Survey Professional Paper 1561: 115 p. • Witherington, Blair. 1992. Crawl identification for Florida Index Beach Surveys. Archie Carr Center for Sea Turtle Research, University of Florida, 5 p. A Back beach facies tract in Cretaceous Fox Hills Sandstone near Limon, Elbert County, Colorado: Showing forebeach (A) and backbeach (B), and collapsed sea turtle nest structure(C) Scale = ~ 10 cm. Back beach facies tract in Cretaceous Fox Hills Sandstone near Limon, Elbert County, Colorado: Showing forebeach (A), backbeach (B), washover fan (C ), and festooned dunes (D&E),. Scale = 1 m.