Dinosaur-landscape interactions at a diverse Early Cretaceous tracksite (Lee Ness Sandstone, Ashdown Formation, southern England)

摘要

An assemblage of dinosaur footprints is reported from the Lower Cretaceous (Berriasian-Valanginian) Ashdown Formation of East Sussex, southern England. The ichnofauna is concentrated around a 2 m thick stratigraphic marker, the Lee Ness Sandstone, where recent cliff retreat has revealed 85 recognisable footprints attributable to 13 morphotypes, many of which bear high-fidelity skin impressions. The newly identified morphotypes mean that this tracksite hosts one of the most diverse dinosaur ichnoassemblages in the well-documented Mesozoic record of Britain; recording the activity of theropod, omithopod, thyreophoran and possibly sauropod trace makers. Most of the footprints were emplaced on a single floodplain mudstone horizon beneath a fluvial crevasse splay sandstone, where preservation was favoured by cohesive sediment and a prolonged interval of sedimentary stasis, during which trackways could be imparted. The sedimentological context of the trackways reveals evidence of interactions between dinosaurs and the riverine landscape that they inhabited; including the development of microtopographies around footprints, which impacted invertebrate burrowing activity, and evidence for dinosaur wading below the bankfull level of small meandering channels and oxbow lakes. Modem analogue suggests that the large dinosaurs may have played a significant role as zoogeomorphic engineers within the ancient floodplain setting, but the imperfect translation of sedimentary environment to sedimentary rock means that geological evidence for such is ambiguous.