Ichnotaxonomy and trackmaker assignment of tetrapod tracks and swimming traces from the middle Permian Hornburg formation of Saxony-Anhalt (Germany)

Abstract

Here we describe new material of tetrapod tracks and swimming traces from the Konberg quarry, a tracksite of the late middle Permian Hornburg Formation in Saxony-Anhalt, central Germany. A relatively well-preserved trackway and several isolated imprints are assigned to Capitosauroides isp. Among others, toe proportions in the manus and pes footprints of the newly described specimens and the long, proximal and detached pedal digit V imprint are similar to the type ichnospecies Capitosauroides bernburgensis from the Early Triassic of Bernburg, Saxony-Anhalt. In these features the new Konberg material differs from other ichnotaxa, such as Amphisauropus and Varanopus, which may look similar in their relative length of the sole, digit proportions and/or in the digit tip imprint morphology. The comparatively large manus imprint, which is wider than long, the relative length and shape of the sole impression, the digit proportions that are indicative for a more ectaxonic manus a more mesaxonic pes, the low pace angulation and the low imprint-size-normalized stride length in the Konberg track type are distinct from C. bernburgensis. It shares, however, a certain similarity with recently described material of Capitosauroides from middle-late Permian tracksites. These observations are in agreement with the results of a multivariate analysis including Capitosauroides and morphologically similar ichnotaxa. Our findings would justify the erection of a new ichnospecies if more trackways with a similar or slightly better preservation were at hand. Hornburg Formation material previously assigned to Amphisauropus is herein considered as indetermined tetrapod tracks, whereas the occurrence of Dromopus isp. is confirmed. This reassignment shortens the stratigraphic range of the ichnogenus Amphisauropus, which appears to be restricted to the early Permian, since younger occurrences are questionable. In agreement with the attribution of Capitosauroides to eutheriodont producers, we regard the Konberg material assigned to this ichnogenus as tracks of small and possibly semi-aquatic therapsids. Abundant tetrapod swimming traces that co-occur with Capitosauroides isp. on the same bedding planes are interpreted as having been made by the same group of producers. The subaquatic traces often consist of short parallel claw mark sets. In agreement with a derived amniote producer group, they indicate propulsion by parasagittal limb movement rather than axial undulation.