Basal dinosauriform and theropod dinosaurs from the mid–lateNorian (LateTriassic) ofPoland: implications forTriassic dinosaur evolution and distribution

Abstract

AbstractThe rise of dinosaurs during theTriassic is a widely studied evolutionary radiation, but there are still many unanswered questions about early dinosaur evolution and biogeography that are hampered by an unevenly sampled Late Triassic fossil record. Although very common in westernNorthAmerica and parts ofSouthAmerica, dinosaur (and more basal dinosauriform) remains are relatively rare in the Upper Triassic deposits ofEurope, making any new discoveries critically important. One of the most diverse dinosauriform assemblages fromEurope comes from thePoręba site inPoland, a recently described locality with exposures of theZbąszynekBeds, which have a palynomorph assemblage characteristic for the mid–late Norian in the biostratigraphic schemes of theGermanicBasin. Using a synapomorphy‐based approach, we evaluate several isolated dinosauriform specimens fromPoręba. This assemblage includes a silesaurid, a herrerasaurid and remains of another type of theropod (potentially a neotheropod). ThePoręba herrerasaurid is the first record of this rare group of primitive dinosaurs fromEurope and one of the youngest records worldwide, whereas the silesaurid is the youngest record of a silesaurid fromEurope. These findings indicate that silesaurids persisted alongside true dinosaurs into the mid–lateNorian ofEurope and that silesaurid–herrerasaurid–neotheropod assemblages (which are also known from theNorian ofNorthAmerica, at low latitudes) were more widespread geographically and latitudinally than previously thought. Silesaurid–herrerasaurid–neotheropod assemblages may have been a common ecological structuring of dinosaurs during their early evolution, and their widespread distribution may indicate weak palaeolatitudinal controls on early dinosaur biogeography during the latestTriassic.