An ornithischian-theropod ichnoassemblage from the Norian-Rhaetian transition of Poland

In this paper, we describe a dinosaur track assemblage from an Upper Triassic fluvial succession at the Lisowice-Lipie Slaskie site in Silesia, southern Poland. The tetrapod tracks were identified in two studied intervals (A and C), each comprising several track-bearing beds, and representing the deposits of meandering fluvial systems. The stratigraphically higher interval C (track-bearing beds a to e) contains Anomoepus isp., attributed to an early ornithischian, as well as Grallator isp., Anchisauripus isp., Apatichnus minor Lull 1915, Apatichnus isp., Eubrontes isp., and cf. Eubrontes isp., attributed to at least six different theropods. As such, the site is one of the richest dinosaur ichnoassemblages from the entire Upper Triassic of the Central European Basin. The track-bearing beds are separated by a bone-bearing succession with skeletal remains of temnospondyls, therapsids and dinosaurs and also contain tracks of non-dinosaurian tetrapods, mainly therapsid tracks. Dinosaur tracks are the most common, representing similar to 70 % of the total number of recorded ichnotaxa. Grallator, Anchisauripus and Apatichnus are the most ubiquitous track ichnogenera, and the fauna represents a rather diverse ornithischian-theropod dinosaur community, without any early dinosauriforms (Atreipus) or sauropodomorphs (Evazoum, Eosauropus, Tetrasauropus), which is also reflected in the skeletal record of the site. Stratigraphical data support a late Norian-earliest Rhaetian age for the tracks. The presence of ornithischian tracks in Lisowice-Lipie Slaskie and anomoepoid-like tracks from a few other Triassic sites suggests that the origin of the ornithischian clade predates the late Norian-early Rhaetian. Moreover, the presence of large eubrontid tracks (Eubrontes and cf. Eubrontes) demonstrates the early presence of large theropods in the region. The new finds offer unique insights into a previously poorly known early dinosaur community from the Late Triassic of northern Pangaea.