Crocodylian Swim Tracks From The Gates Formation (Albian), British Columbia, Canada: Comparisons With Cretaceous Crocodylian Ichnology In Western Usa

Numerous crocodylian swim tracks occur in the late Early Cretaceous and earliest Late Cretaceous of western North America, in coastal plain deposits marginal to the Cretaceous interior seaways. New as-semblages from the lower Albian Gates Formation, within the Tumbler Ridge UNESCO Global Geopark Quintette site (TRUGG-Q) in British Columbia, Canada, resemble those from Albian-Cenomanian Dakota Sandstone sites in Colorado, Kansas and Utah, and facilitate comparative analysis of how such assem-blages are registered and preserved. The Gates Formation track assemblage formed on the southwest margin of the 'Moosebar Sea' that filled the foredeep of the Western Canada Foreland Basin in the Early Albian. Northeast-prograding sandy deltas were backed by low-lying and heavily-vegetated coastal plains, inhabited by track-making dinosaurs, birds, and crocodylians. The base of a tidal channel-fill at the TRUGG-Q site preserves crocodylian swim traces indicating progression largely parallel to the channel axis, as also inferred for some USA sites. Swim track lengths can be categorized on a shortelong spectrum which reflects swimming behavior, with short, wide toe tip traces indicating firm digging-in of toes ('punting' or 'poling' behavior), and elongate scrape marks indicating light touch-down (or substrate 'raking') by buoyant animals making intermittent contact with a subaqueous substrate. The body lengths size of crocodylian trackmakers can be calculated from rare complete 'walking' track footprints or from the widths, not lengths, in the case of 'swim' traces. The mean size of the Canadian tracks indicates individuals with body lengths in the range of-1.0 m, with larger trackmakers up to-4.0 m more common at the USA sites. (c) 2021 Elsevier Ltd. All rights reserved.