Testing the utility of interdigital angle as a taxonomically informative variable in tridactyl dinosaur ichnology

Jack B. Davidson¹, James O. Farlow², Todd L. Green³ & Jordan C. Mallon^1,4
1Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada. *Current address: School of GeoSciences, University of Edinburgh, Grant Institute, the King’s Buildings, James Hutton Road, Edinburgh EH9 3FE, UK.
²Department of Geosciences, Indiana-Purdue University, Fort Wayne, Indiana, USA.
³Department of Biomedical and Anatomical Sciences, New York Institute of Technology College of Osteopathic Medicine at Arkansas State University, Jonesboro, Arkansas, USA.
⁴Beaty Centre for Species Discovery and Palaeobiology Section, Canadian Museum of Nature, Ottawa, Ontario, Canada.
Corresponding author e-mail: jmallon@nature.ca

Interdigital angle is one of many metrics used to identify tridactyl dinosaur trackmakers. However, there is disagreement about the taxonomic significance of this metric, and some have argued that extramorphological factors may overwhelm any intrinsic signal. The present study assesses the taxonomic utility of interdigital angle by examining variation in the divarication of the distal metatarsals, a proxy for toe splay. We find evidence for allometric variation in metatarsal divarication and group differences in the same, although these patterns are often subtle and methodologically contingent. Nonetheless, these group differences offer some reason to suspect that interdigital angle is taxonomically informative.

ichnology, dinosaurs, tracks, interdigital angle, metatarsus.