History of Ichnology: The Misconceived Footprints of Rhynchosaurs

Abstract

In 1842 Richard Owen described a Triassic reptile from Grinshill, Shropshire, which he named Rhynchosaurus articeps. He suggested that footprints found in the same beds were those of this fossil. However, the footprints were characterised by a backward-pointing toe and so were of the type now known as Rotodactylus. Huxley (1877), Woodward (1907), and Benton (1990) have subsequently shown that the five digits of Rhynchosaurus point forward and so could not have left these footprints. In 1896 Beasley classified the Triassic footprints found in Cheshire, his type D prints being those earlier assigned to rhynchosaurs. His D1 prints were named Rhynchosauroides articeps by Maidwell (1911). However, these D1 prints, which come from a lower horizon in the Anisian, are consistently too small to match Owen's fossil. Beasley's D3 form, now named Synaptichnium pseudosuchoides Nopcsa, is more likely to represent the footprints of Rhynchosaurus articeps, although further research and study of more complete trackways will be necessary to clarify whether these are the footprints of Archosauromorphs, such as rhynchosaurs or possibly those of Archosauriformes, for example, erythrosuchids or proterosuchids. Maidwell's Rhynchosauroides rectipes and Rhynchosauroides membranipes, originally believed to be distinct ichnospecies, are more likely to be synonyms, their apparent differences reflecting variations in the substrate traversed.

Keywords:

• Footprints
• Ichnotaxonomy
• Rhynchosauroides
• Triassic

ACKNOWLEDGMENTS

Unstinting assistance, particularly with the preparation of illustrations, was provided by Wendy Simkiss and Alan Bowden of the Earth Sciences Department of the National Museums Liverpool (NML) where Geoffrey Tresise is Honorary Curator. The ledgers and photographic archive of Henry Beasley (the property of the Liverpool Geological Society) are stored in the NML archives.

Michael J. King's initial work was undertaken in the course of postgraduate research funded by NERC, and under the supervision of Professor Mike Benton of the University of Bristol. For a full list of the many individuals and institutions assisting in this research, please refer to an earlier ICHNOS paper (King et al. 2005).