The Late Triassic Tetrapod Ichnotaxon Apatopus Lineatus (bock 1952) and Its Distribution

The tetrapod ichnotaxon Apatopus lineatus is a relatively uncommon component of Late Triassic footprint assemblages. This might be related to the semi-aquatic lifestyle of the trackmakers, which were almost certainly phytosaurs and whose skeletons are known from coeval deposits with a Pangea-wide distribution. Originally described from the Passaic Formation of New Jersey, Apatopus lineatus has been reported from other localities and horizons in the Newark Supergroup and from the Chinle Group of the American Southwest. In recent years, new discoveries of Apatopus footprints and trackways have been made in North America, North Africa and Europe. A footprint with skin impressions from the Passaic Formation of Pennsylvania and material from the Stuttgart and Hassberge formations (Carnian) of Germany is described here for the first time. Parallel to the osteological record of phytosaurs, the ichnotaxon Apatopus lineatus reflects a widespread group of archosaurs living in habitats that only randomly overlapped those of fully terrestrial chirotherian trackmakers. The reevaluation of the phylogenetic position of phytosaurs in recent studies and the supposed stratigraphic range of Phytosauria from the Early to the Late Triassic suggest a terrestrial lifestyle for early members of the group and a later adaptation to aquatic environments, similar to the evolutionary developments in crocodylomorphs that took place in the Jurassic-Cretaceous. Morphologically and temporally, some chirothere footprints from Early-Middle Triassic deposits such as Synaptichnium could fill this gap in the early record of Phytosauria.