A new recumbirostran 'microsaur' from the lower Permian Bromacker locality, Thuringia, Germany, and its fossorial adaptations

Several recumbirostran 'microsaurs' are known from early Permian sites across Germany, including the Tambach Formation in Thuringia, central Germany. The only 'microsaur' thus far described from the Tambach Formation was the ostodolepid recumbirostran Tambaroter carrolli. However, there is also the documented presence of an undescribed recumbirostran 'microsaur' at the well-known Bromacker locality. The Bromacker locality is highly recognized and best known for its very diverse and extremely well-preserved terrestrial tetrapod assemblage combined with the co-occurrence of an exceptional vertebrate ichnofossil record. Here we describe a second new recumbirostran taxon from the Tambach Formation, which is also the first from the Bromacker locality itself. Phylogenetic analysis indicates that the new taxon, Bromerpeton subcolossus gen. et sp. nov., is a brachystelechid recumbirostran, a group also known elsewhere in Germany. The following features differentiate Bromerpeton from the other members of the clade: the presence of 13 maxillary teeth, narrow postorbitals that do not substantially contribute to the postorbital region of the skull, the frontal does not contribute to the orbital margin, and the presence of five manual digits. This new recumbirostran 'microsaur' further adds to the unique ecosystem that is preserved at the Bromacker locality, granting us a better understanding of what was living underfoot the larger more well-known animals at the locality. Likewise, it expands our understanding of the evolution of recumbirostran 'microsaurs', especially with regards to digit and limb reduction within the clade.

An earliest Triassic age for Tasmaniolimulus and comments on synchrotron tomography of Gondwanan horseshoe crabs

Constraining the timing of morphological innovations within xiphosurid evolution is central for understanding when and how such a long-lived group exploited vacant ecological niches over the majority of the Phanerozoic. To expand the knowledge on the evolution of select xiphosurid forms, we reconsider the four Australian taxa: Austrolimulus fletcheri, Dubbolimulus peetae, Tasmaniolimulus patersoni, and Victalimulus mcqueeni. In revisiting these taxa, we determine that, contrary to previous suggestion, T. patersoni arose after the Permian and the origin of over-developed genal spine structures within Austrolimulidae is exclusive to the Triassic. To increase the availability of morphological data pertaining to these unique forms, we also examined the holotypes of the four xiphosurids using synchrotron radiation X-ray tomography (SRXT). Such non-destructive, in situ imaging of palaeontological specimens can aid in the identification of novel morphological data by obviating the need for potentially extensive preparation of fossils from the surrounding rock matrix. This is particularly important for rare and/or delicate holotypes. Here, SRXT was used to emphasize A. fletcheri and T. patersoni cardiac lobe morphologies and illustrate aspects of the V. mcqueeni thoracetronic doublure, appendage impressions, and moveable spine notches. Unfortunately, the strongly compacted D. peetae precluded the identification of any internal structures, but appendage impressions were observed. The application of computational fluid dynamics to high-resolution 3D reconstructions are proposed to understand the hydrodynamic properties of divergent genal spine morphologies of austrolimulid xiphosurids.