Integration of tetrapod ichnofaunas and coastal dynamics for paleocommunity reconstruction in the Curtis and Summerville formations (Jurassic), eastern Utah

Abstract

ABSTRACT The transition between the aeolian Moab Member of the Curtis Formation and the marginal marine upper tongue of the Summerville Formation, in the area of Arches National Park, Utah, facilitated the registration of the distinctive theropod-dominated Moab Megatracksite complex, which is something of an ichnological cause célèbre. The complex reveals three interpenetrating ichnofaunas each with distinctive ichnofacies characteristics. The present study focuses on the small theropod-dominated assemblages from the coastal dune facies and applies Walther’s Law of Facies to the sequence relationship between onshore ichnoassemblages, the late pulse of transgression by the Summerville sea, and the development of the shallow marine Pteraichnus ichnocoenosis. Together, these spatio-temporal facies relationship between onshore terrestrial, shoreline and shallow marine facies and their contained ichnofaunas shed useful light on the Late Jurassic tetrapod ecology of the region, in an area entirely lacking tetrapod body fossils. The small theropod dune ichnofauna has obvious precursors in other Jurassic dune facies. The shoreline and shallow marine ichnocoenosis also fit certain ichnofacies models, despite the lack of comparable ichnofaunas in the area. Abundant trackway size frequency data yield body mass estimates which allow testing of recently proposed palaeobiological theories on theropod ontogeny and community structure based on the skeletal record.