PROBABLE AVIAN FEEDING TRACE FOSSILS FROM THE CEDAR MOUNTAIN FORMATION (LOWER CRETACEOUS), UTAH USA

The Cedar Mountain Formation (Early Cretaceous, Valanginian-Albian) of Utah (USA) is world famous for its dinosaur body fossils, but is also becoming more recognized for its vertebrate trace fossils, such as non-avian and avian dinosaur tracks. Locally abundant linear grooves in fluvial sandstones of the Cedar Mountain Formation, which we interpret as bird feeding traces, add to its vertebrate ichnodiversity. Grooves occur in the Ruby Ranch Member at Arches National Park and Yellow Cat Member on BLM land northwest of Arches. The trace fossils, which have regular lengths (14-18 mm), widths (3-4 mm), and depths (1-2 mm), generally consist of parallel sets or arc-like to radial patterns in shallow depressions. Grooves share the same beds with wrinkle marks, laminations, invertebrate trails, non-avian theropod tracks, and rare avian tracks. Wrinkle marks and laminations imply sedimentary surfaces bound by microbial films, which would have helped preserve grooves and other surficial trace fossils. Forms and patterns of the grooves do not match any known inorganic structures, invertebrate traces, or fish traces. As a result, we conclude they are feeding traces made by animal beaks used to gouge underneath and parallel to microbial films. Dimensions and patterns of the trace fossils suggest relatively small vertebrate tracemakers, such as birds, although small pterosaurs are also possible. To make these patterns, tracemakers would have systematically mined the surface by moving laterally and/or circularly. In this sense, the trace fossils are comparable to modern shorebird “mining” traces, such as those made by sanderlings or plovers, and thus potentially represent remarkably contemporary behavior in Early Cretaceous birds. Based on detrital zircon and C-isotope chemostratigraphic evidence, the Ruby Ranch Member in this area is constrained to the late Aptian to Albian. Bird tracks documented in the upper Yellow Cat Member of the Cedar Mountain Formation (potentially as old as Valanginian) also support a presence of possible avian tracemakers through a significant amount of time represented by the Cedar Mountain Formation. Owing to their distinctive forms and patterns, as well as stratigraphic recurrence in the Cedar Mountain Formation, we plan to propose a new ichnogenus and ichnospecies for this trace fossil.