Exceptional preservation processes of 3D dinosaur footprint casts in Costalomo (Lower Cretaceous, Cameros Basin, Spain)

Terra Nova, 24, 136–141, 2012

Abstract

Theropod dinosaur footprints at the Costalomo tracksite (Pinilla de los Moros Formation, Upper Hauterivian–Lower Barremian, western Cameros Basin, Salas de los Infantes, Burgos Province, Spain) show unusual preservation of a previously undescribed nature. The footprints occur as casts (positive epireliefs) at the top of a sandstone bed and preserve exceptional details of the top of the digit and claw morphology, and of digital interactions with the sediment during penetration and extraction from the sediment. Footprint formation and preservation occurred in the following stages: (1) The dinosaur stepped on a thin (4–8 cm thick) mud layer, its foot sinking to contact an underlying sand layer (channel fill); (2) voids left in the cohesive mud after foot withdrawal were later filled with sand; (3) subsequent deposition, burial and Alpine compression indurated the muds and the sands of both the footprint casts and the underlying channel sand layer; and (4) modern erosion exposed the footprint casts, by removing the mud above the sandstone.