Pterosaur swim tracks and other ichnological evidence of behaviour and ecology

Abstract

AbstractNew finds of pterosaur tracks (cf. Pteraichnus) from the Summerville and Sundance formations (Late Jurassic) of western North America associated with elongate scrape marks and small circular paired depressions indicate that pterosaurs could swim, or at least float in water, and that they may have fed on small animals living at the sediment surface in shallow water. In this respect their behaviour resembled certain seabirds. The ichnological evidence for pterosaur ‘swim’ and ‘feeding’ traces consists of scrape marks interpreted as traces left when the paddling limb of a pterosaur registered on the substrate, and small circular paired depressions as traces left when the beak of a pterosaur was probing for food. Such traces resulting from aquatic activity are consistent with the nearshore environments in which pterosaur bones and trackways have been found.There is growing evidence for an extensive and complex Pteraichnus ichnofacies in the Late Jurassic of western North America; over 80 specimens have been collected with many more remaining in the field. In particular we draw attention to the large quantitative data base that is available for morphometric, size-frequency studies and the potential for behavioural studies of individual locomotion and flocking. In addition the sites hold considerable promise for understanding what appears to be the world’s largest pterosaur ichnofacies in the context of ancient depositional environments and regional sequence stratigraphy.