DELTA PLAIN BLOAT AND FLOAT TAPHONOMY IN THE CRETACEOUS (CENOMANIAN) WOODBINE FORMATION AT THE ARLINGTON ARCHOSAUR SITE DINOSAUR QUARRY, NORTH TEXAS

The Arlington Archosaur Site (AAS), located in the city of Arlington, Tarrant County of North Central Texas is an urban fossil site that has produced the remains of Cretaceous vertebrates. The vertebrates range from dinosauria, crocodilian and chelonian to elasmobranch and dipnoan. All of the AAS fossils occur within the coastal Mid –Cretaceous (Cenomanian; 95 Mya) Woodbine Formation. The environments of the Woodbine at the AAS are coastal delta plain; shales interbedded with conglomeratic sandstones, overlaying an inundated mudstone (paleosol), rich with organic material that overlies a peat bed. Ornithopod (Dinosauria:Ornithopoda) remains were recovered from the inundated delta plain mudstone. The ornithopod remains are well preserved, but primarily represent one half of the animal’s skeleton. Among the recovered elements are; a left ilium, ischium and pubis, a partial femur, a scapula and coracoid, left dorsal ribs, along with cervical, dorsal and caudal vertebrae. The ornithopod fossils show no signs of abrasion via transport, yet some key elements are missing. This implies rupturing of the ornithopod body and scattering of miscellaneous skeletal elements along the delta plain. Such patterns are found in the fossil record under conditions referred to as “bloat and float”, where an animal carcass bloated with post mortem gasses floats a given distance, then ruptures and sinks. The pattern of bone dispersal and preservation implies bloat and float taphonomy at the Arlington Archosaur Site Dinosaur Quarry.