The fossil trackway Pteraichnus is pterosaurian, not crocodilian: Implications for the global distribution of pterosaur tracks

There has been much confusion regarding the fossil footprint record of pterosaurs, with both non‐pterosaurian tracks assigned to pterosaurs, and pterosaurian tracks assigned to non‐pterosaurian track‐makers such as crocodilians and turtles. Various authors have also debated whether pterosaurs were bipedal or quadrupedal, erect or semi‐erect, digitigrade or plantigrade, when progressing on land. Recent claims that Pteraichnus was made by a crocodilian effectively implied that there are no known pterosaurian tracks in the fossil record.

We show here, on the basis of new material from the Jurassic Sundance and Summerville formations of Wyoming and Utah, and other Jurassic and Cretaceous sites in Europe and North America, that pterosaur tracks are now quite widely known and indicative of quadrupedal progression on land. The fossil trackway Pteraichnus is pterosaurian in origin as originally proposed by Stokes (1957), and not crocodilian as suggested by Padian and Olsen (1984). The animals responsible for making Pteraichnus tracks were plantigrade, semi‐erect and quadrupedal, and carried a majority of their body weight on their front limbs. Pes and manus track morphology, as well as trackway pattern are strikingly consistent with pterosaur anatomy. In supporting the original interpretation of Stokes, we do not challenge all other reassessments of purported pterosaur tracks that have been attributed to crocodiles. We agree with the crocodilian interpretation in some instances, but note that in such cases the tracks are not attributable to the ichnogenus Pteraichnus.

It appears that abundant Pteraichnus tracks attributable to more than one ichnospecies are widely distributed in a very narrow Mid‐Late Jurassic stratigraphie interval (Sundance‐Summerville‐lower Morrison beds) in western North America at a time when pterosaur diversity was very high. We therefore erect the new ichnospecies Pteraichnus stokesi to accommodate a distinctive well‐preserved trackway that differs from P. saltwashensis. The paleoenvironmental occurrence of some tracksites, along marine shorelines, is also consistent with the inferred habitat of pterosaurs.

A Pteraichnus trackway is also known from the Cretaceous of Spain, and various other isolated Pteraichnus ‐like tracks are known from other Jurassic and Cretaceous deposits in Europe and North America, sometimes in association with freshwater depositional environments.

Key words:

• pterosaur tracks
• quadrupedal locomotion