FIRST REPORT ON DINOSAUR TRACKS FROM THE BURRO CANYON FORMATION, SAN JUAN COUNTY, UTAH, USA – EVIDENCE OF A DIVERSE, HITHERTO UNKNOWN LOWER CRETACEOUS DINOSAUR FAUNA

摘要

The newly discovered White Mesa tracksite in the Burro Canyon Formation represents a snapshot of a diverse, Lower Cretaceous dinosaur fauna from south-eastern Utah. The tracks were found at a construction site where the sandstone had been bulldozed and broken up. All tracks were found as deep, well-preserved natural casts on the underside of the sandstone slabs. Individual theropod tracks are 19–57 cm in length; one peculiar track shows evidence of a possible pathological swelling in the middle of digit III and an apparently didactyl track is tentatively assigned to a dromaeosaurid. Individual sauropod tracks are found with pes lengths of 36–72 cm, and interestingly, three distinct shapes of manus tracks, ranging from wide banana shaped to rounded and hoof-like. Ornithopods are represented with individual tracks 18–37 cm in length; a sin gle track can possibly be attributed to the thyreophoran ichnogenus Deltapodus . Zir con U-Pb dating places the track-bearing layer in the Barremian, contemporary to the lower Yellow Cat Member of the Cedar Mountain Formation, which has a similar faunal composition based on both tracks and body fossils. This new track-fauna demonstrates the existence of a diverse dinosaurian assemblage in the lower part of the Burro Canyon Formation, which hitherto is not known to yield skeletalre mains.