6 Undergraduate Research (Posters)

Monday, 16 March 2009
8:00 AM - 6:00 PM

COPROLITES OF THE ARLINGTON ARCHOSAUR SITE, WOODBINE FORMATION (CENOMANIAN; 95 MYA), NORTH CENTRAL TEXAS

Paper number: 6-9
Program: Theme Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

This project reports the first occurrence of coprolites found in the Woodbine Formation (Cenomanian; 95 mya) of North Texas. Within the Woodbine Formation, a collection of coprolites has been recovered from the Arlington Archosaur Site. The depositional environment is a near shore coastal embayment and Gyttja style channel fill; fine grained sediments (mud and clay), rich with organic material at the base of the section. At the site, approximately 80 coprolites have been recovered throughout the section, that demonstrates a variety of morphologies suggestive of multiple taxa. Sizes range from 3cm – 19.5 cm in length and 2 cm – 30cm in diameter, with dinosaur and crocodile being the largest. The morphologies of the specimens are cylindrical, spiral and ovoid. The cylindrical coprolites are interpreted as crocodilian intestinal tract material, based on size, morphology and content. The spiral specimens have a pronounced external spiral that coils to the end; isopolar and amphipolar. The spiral coprolites are indicative of marine taxa; shark and fish. Spiral coprolites are typically associated with the shark Hybodus. At the Arlington Archosaur Site, both Hybodont and Cretodus teeth and spines are present and interpreted as the source. The large (20x30 cm) ovoid coprolites are indicative of dinosaur. Most of the specimens recovered are preserved intact, not flattened, undeformed and retain the original shape. This is indicative of rapid burial in a low energy environment, immediately after defecation.

Thin sections made of sampled specimens show evidence of diet, principally coral and fragmentary bivalve shell along with fragmentary bone, scales, plant and gastropod shell. Thin section analysis indicates typical species' trace, both predator and prey. The fish and shark coprolites contain mixed coral and shell remains along with small bone fragments and scales. The large dinosaur coprolites contain fragmentary wood and plant debris, typical of ornithopod diets. Coprolites have previously been established as ecological and environmental indicators in the Eagle Ford Shale (Turonian) of North Texas, primarily marine taxa. This analysis of the Woodbine coprolites illustrates the nature of the regional coastal environments, as a mix of both marine and terrestrial taxa have been recovered from the Arlington Archosaur Site.