PREDATORY BEHAVIOR OF A GIANT CROCODYLIFORM FROM THE WOODBINE FORMATION (CENOMANIAN) OF TEXAS

There is little direct evidence of feeding behavior in Mesozoic crocodyliforms. Here we report the remains of a possible crocodyliform feeding ground from the Cretaceous of Texas. The fossil locality, known as the Arlington Archosaur Site (AAS), occurs in exposures of the Woodbine Formation in Tarrant County. The AAS preserves components of a coastal delta-plain ecosystem, including dinosaurs, crocodyliforms, turtles, and lungfish. Feeding traces consist of pits, scores, and a puncture that occur on multiple turtle shell fragments and two dinosaur limb bones. These traces are attributed to a crocodyliform based on diagnostic bite marks and comparisons to the morphology of the AAS crocodyliform. Marks on shells suggest an inertial feeding strategy followed by crushing. Dinosaur bones come from juvenile individuals and the marks are consistent with traces produced during disarticulation of prey by living crocodylians. The feeding ecology implied by these traces is similar to that of modern generalist crocodylians inhabiting similar environments. Considering the number of diagnosable crocodyliform feeding traces, numerous shed crocodyliform teeth, and the comparative absence of feeding traces from other predators, the AAS crocodyliform is interpreted as the apex predator.

In association with the vertebrate fossils, 150 coprolites were recovered, demonstrating cylindrical, spiral, and scroll morphologies. The cylindrical coprolites are interpreted as crocodyliform intestinal tract material while scroll morphologies are assigned to general reptilian and possible crocodyliform. The coprolites are not deformed, and retain their original shape. This is indicative of rapid burial in a low energy environment soon after defecation. In modern coastal plains, crocodylians live and feed together in regions referred to as feeding grounds. The coprolites, turtle shells, teeth, and archosaur remains were mapped within a single horizon, and were disarticulated. Their association is interpreted as evidence of a crocodyliform feeding ground. Crocodyliforms therefore are not only important predators in ecosystems but also played an important taphonomic role in the assembly of vertebrate remains from the surrounding community through the formation of feeding grounds.