MAPPING AND EXCAVATING MID-CRETACEOUS (CENOMANIAN) CROCODILES AT A LARGE URBAN DIG: THE ARLINGTON ARCHOSAUR SITE, NORTH TEXAS

The Arlington Archosaur Site (AAS) located in North Texas has produced the fossil remains of a variety of Cretaceous vertebrates. The vertebrate fossils represented at the site range from dinosauria, crocodilian, to chelonian and dipnoan, with crocodilian and chelonian being most common. The site is located within the Mid–Cretaceous Woodbine Formation (Cenomanian). The paleoenvironment of the Woodbine at the AAS is a coastal delta plain consisting of a paleosol, rich with organic material, which overlies a peat bed. During the 2009 summer field season, a large Cretaceous crocodile was excavated from the peat bed in a hectic one week dig. Due to the urban location of the site, an emergency excavation was organized in an unusual manner using the online networking site, Facebook. Utilizing a Facebook group set up for the AAS, a volunteer team was assembled within 24 hrs to assist in the excavation. The dig ran for 7 days, in what is now known as “Crocorama”. During Crocorama numerous elements of a large adult Cretaceous crocodile were recovered from the site as well as elements of an unidentified chelonian. The site was mapped using Cartesian coordinates in a 5m x 2.5m grid system. Each fossil was located and drawn in on the grid prior to removal from the field. Each fossil was wrapped and stored for transport with coordinates recorded on the jacket, as well as on the site map.

As the site expanded in 2010, other grids were developed by extending the coordinate system to the north, east and west. The grid coordinates were marked with a GPS, and later digitized. In May of 2010, juvenile crocodiles were discovered near the Crocorama site. Later named the Nursery, the new site was added into the Crocorama map grid. Several juvenile individuals were recovered (1/5 the size of the adult); all bones show a gentle NE-SW trend similar to the bones in the original Crocorama quarry. Approximately 200 meters to the south and 150 meters to the east of the original Crocorama grid, a new crocodile site named Croc-Cove was mapped in July of 2010. The new site was added into the Crocorama master grid system using a spreadsheet program which converts any GPS reference point into a point that can be referenced back to the master grid. The AAS maps not only document the location of the fossils for taphonomic purposes but may also be used to address questions on crocodile behavior.