Prorotodactylus and Rotodactylus tracks: an ichnological record of dinosauromorphs from the Early–Middle Triassic of Poland

Abstract

AbstractWe present the first comprehensive description of Prorotodactylus and Rotodactylus dinosauromorph tracks from the Early and Middle Triassic of the Holy Cross Mountains, Poland. We describe and comprehensively figure tracks that have been mentioned briefly in previous accounts as well as new, recently discovered material, and analyse the variation and stratigraphic distribution of these specimens. Tracks have been recorded from four sites – Koszary, Stryczowice, Wióry and Baranów – which span the early Olenekian–early Anisian (c. 250–246 Ma). These tracks therefore represent an ichnological record of the evolutionary succession of early dinosauromorphs during the earliest part of their evolutionary history. Recognized track types include cf. Prorotodactylus isp., Prorotodactylus isp., Prorotodactylus mirus, Rotodactylus cursorius, Rotodactylus isp. and cf. Rotodactylus isp. At least three distinct Early and early Middle Triassic early dinosauromorph ichnofaunas can be recognized. The oldest, which is early Olenekian in age, is characterized by the presence of Prorotodactylus isp., cf. Prorotodactylus isp. and non-archosaurian archosauromorph or archosaur tracks (e.g. Synaptichnium isp., Protochirotherium isp.), recorded at the Stryczowice and Koszary sites. The following assemblage, recorded at the late Olenekian Wióry site, displays the highest ichnodiversity of dinosauromorphs, with four track types present (Prorotodactylus isp., Prorotodactylus mirus, Rotodactylus cursorius and cf. Rotodactylus isp.). The youngest site, Baranów, includes Rotodactylus isp., as well as other larger dinosauromorph tracks. The first body fossil evidence of dinosauromorphs is a few million years younger than the youngest Polish tracks, so Prorotodactylus and Rotodactylus tracks currently provide the oldest record of dinosauromorph morphology, biology and evolution.