Probable Relationships between the Lower Jurassic Crocodilomorph Trackways Batrachopus and Selenichnus: Evidence and Implications Based on New Finds from the St. George Area Southwestern Utah

Abstract

The enigmatic ichnogenus Selenichnus (Hitchcock, 1858) from the Lower Jurassic of Massachusetts and Utah may represent poorly preserved, extramorphological examples of Batrachopus. Selenichnus trackways from the St. George area (Utah) are virtually indistinguishable from the type material described by Hitchcock (1858) and Lull (1953) from Massachusetts. However, Selenichnus type specimens from Massachusetts, as well as the material from Utah, suggest a relationship with Batrachopus: The former track morphology appears to transform into the latter as preservational conditions change. The size and gait indicated by the two ichnogenera are similar. The suggested relationship between the two ichnogenera does not alter the fact that there are distinct differences in the morphology of the type specimens. Thus, pending discovery of more material, formal synonymy of the two ichnogenera is not formally proposed.

Keywords:

• Crocodilomorph tracks
• Batrachopus
• Lower Jurassic

ACKNOWLEDGEMENTS

We thank Adrian Hunt, New Mexico Museum of Natural History and Science, and John Foster, Museum of Western Colorado, for their helpful reviews of the manuscript. Special thanks go to Sheldon and LaVerna Johnson and Theresa Walker for their tireless efforts to preserve the St. George tracksite. Thanks also to Darcy Stewart and Kay Lee Harper, for their help finding specimens in the field. Partial costs for fieldwork and manuscript preparation were provided by the University of Colorado at Denver Dinosaur Trackers Research Group and the Utah Geological Survey and the City of St. George.

Notes

Since this paper was written and revised, there have been many additional discoveries of Batrachopus tracks and trackways at the St. George site. The ichnogenus should not be considered as uncommon as was first thought.