Differentiating sauropod from thyreophoran tracks: insights from the Late Jurassic Villette Tracksite (Jura, France)

Lara Sciscio ^1,2,4, Christian A. Meyer ^3,4, Emmanuel Fara ⁵, Patrice Landry ⁶, Jean-David Moreau ⁷ & Nicolas Olivier ^8
1JURASSICA Museum, Route de Fontenais 21, 2900 Porrentruy., ²Département des Géosciences, Université de Fribourg, Chemin du Musée 6, 1700 Fribourg., ³Departement of Environmental Sciences, University of Basel, Bernoullistrasse 32, CH-4056 Basel., ⁴Museo de Historia Natural Alcide d’Orbigny Avenida Potosi N-1458 Cochabamba, Bolivia., ⁵Université Bourgogne Europe, CNRS, Biogéosciences UMR 6282, 6 Boulevard Gabriel, 21000 Dijon, France., ⁶Association Ain-Bugey-Géo-Découvertes Oyonnax, France., ⁷Université Paris-Saclay, CNRS, GEOPS, 91405 Orsay, France., ⁸Laboratoire Magmas et Volcans, Université Clermont Auvergne, CNRS, IRD, OPGC, F-63000 Clermont-Ferrand, France.

Sauropod trackways are extensively reported from Upper Jurassic deposits, whereas thyreophoran tracks seem to be rarer and often overlooked or misidentified due to their morphological similarity to sauropod tracks. This overlap complicates ichnological interpretations, leaving several occurrences unresolved. Here, we analyse an ambiguous trackway from the Late Jurassic (Kimmeridgian) Villette tracksite in eastern France (Jura Mountains), part of a sauropod-dominated ichnoassemblage. The trackway displays morphological features typical of Deltapodus, an ichnogenus attributed to thyreophoran (stegosaur) trackmakers, including the size, overall gross pes and manus morphology, and track orientation. Using photogrammetry and morphometric analyses, we compare the Villette trackway with contemporaneous Deltapodus and Deltapodus-like trackways and sauropod trackways of the Swiss Jura mountains. Considering this, despite notable similarities, key differences, such as the shape of the pes tracks, presence of a strong heel impression, and the absence of three-toed digit impressions, exclude assignment to Deltapodus and support attribution to a small-bodied sauropod trackmaker. This conclusion is consistent with the ichnoassemblage at Villette, where other tracks correspond to Parabrontopodus-like ichnotaxa, reinforcing a sauropod attribution. More broadly, this study also synthesizes key diagnostic criteria and methodological approaches that help in distinguishing thyreophoran from sauropod tracks. By integrating these methods, we highlight their potential as reliable tools for ichnological interpretation, providing a framework for future studies addressing similar challenges.