The complexity of tracking stegosaurs and their gregarious behavior

Abstract

Stegosaur tracks were unknown until the identification of Deltapodus more than 20 years ago. Currently, the Iberian Peninsula, especially Teruel Province, is one of the areas globally with the most occurrences of these tracks. However, their identification, based on the global record, is problematic due to their similarities with sauropod tracks. A review of the largest number of analyzed Deltapodus tracks globally, including the holotype of D. ibericus and a description of new occurrences, has been carried out. Our research shows substantial morphological variations, but all the studied tracks can be considered D. ibericus based on the manus morphology and the morphometric data. These variations are related to substrate differences and/or different dynamic foot postures (possibly ontogenetically related) during locomotion, as evidenced by changes within the same trackway. We provide detailed comparisons via 3D modeling with sauropod tracks, and our data show that they generally have proportionally longer manus and wider pes because of the differences in the metapodial bones. The scarcity of stegosaur trackways in the fossil record has prevented the identification of gregarious behavior in this group of herbivorous dinosaurs. Two of the studied tracksites show evidence of this behavior, being the only examples among stegosaurs described thus far in the fossil record.