Crocodylomorph Trackways from the Jurassic to Early Cretaceous of North America and Europe: Implications for Ichnotaxonomy

Abstract

Trackways described as Batrachopus (Batrachopodidae Lull, 1904) from the Lower Jurassic of Europe are rare and in some cases different from the type trackways from North America. Differences may be in part attributable to preservation, but current evidence suggests that there is inherent variability in Batrachopodidae morphotypes, beyond that attributable to differential preservation. Type Batrachopus is a stout-toed form, with minimal digit divarication (i.e., a long foot), whereas Antipus describes slender-toed forms with a wider foot and wider digit divarications.

Antipus is also similar to Crocodylopodus (ichnofamily Crocodylopodidae: Fuentes Vidarte and Meijide Calvo, 1999) from near the Jurassic-Cretaceous boundary in Spain. Crocodylopodus has a relatively large manus, and a less outwardly rotated trackway, but is not sufficiently different from Batrachopodidae to warrant its own ichnofamily. Manus-pes size (area) ratios (heteropody) may also be important in differentiating different crocodylomorph ichnotaxa, as is the case with other archosaurian ichnotaxa. However, heteropody may change with size, and be less pronounced in large individuals. Manus and pes rotation patterns, and trackway width are variable and may be of use for differentiation of ichnotaxa but may also be a function of speed.

Keywords:

• Antipus
• Batrachopus
• crocodylomorph tracks

ACKNOWLEDGEMENTS

We thank Adrian Hunt, New Mexico Museum of Nature and Science and Martin Whyte, University of Sheffield, for their helpful reviews. We also thank Christian Montenat of the Albert Lapparent Institute of Geology, Paris, for help with access to specimens in their collection. Many thanks to Antoine Heitz for donating an important specimen to the collection of the Natural History Museum in Basel.