Autopod and track morphology elucidate on the putative producer in hadrosauriform ornithopods: a case study of manus tracks from the Frontier Formation (Coniacian), Montana

ABSTRACT

Hadrosauriformes is a group of ornithopod dinosaurs with a rich and extensive Cretaceous track record. However, their rear foot (pes) anatomy is rather conservative. Thus, distinguishing different putative track producers from morphological differences is often impeded unless their identification is corroborated by stratigraphic and geographic distribution. On the contrary, the forefoot (manus) anatomy of hadrosauriform taxa reflects distinctive characters that, when preserved in tracks, may be critical for identifying their trackmakers. In this study, we examined three manus tracks preserved as sandstone casts, collected from Coniacian deposits of the Frontier Formation, southwestern Montana, USA. Tracks are assigned to Hadrosauriformes according to their steeply inclined morphology, functionally tridactyl condition, presence of hoof-like impressions and crescentic cross-sectional shape. Track preservation suggests that digit II could be extended medially, whereas movements for digits III and IV were limited. The dorsally curved digit II and III impressions indicate that these digits could be hyperextended. One track shows a short, spade-like ungual II impression, suggesting a closer affinity of its producer to hadrosauroid or hadrosaurid ornithopods. Osteological characters of the manus combined with track morphology can help with discerning different hadrosauriform producers, providing important implication for palaeoecological and palaeogeographical reconstructions.

KEYWORDS:

• Ornithopod tracks
• Hadrosauriformes
• Frontier Formation
• Coniacian

Acknowledgments

We are thankful to the Bureau of Land Management and US Forest Service staff for the support provided during our research. We want to express our gratitude to E. Metz, J. Scannella, and all the Museum of the Rockies ‘staff for helping in specimen logistic and curation. We are also indebted to T. Dyman, W.J. Freimuth, I. Aguilar for their assistance in the field. Finally, we would like to thank J. Lallensack and the anonymous reviewer whose comments greatly improved the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental data

Supplemental data for this article can be accessed online at https://doi.org/10.1080/08912963.2023.2196683.