Walking with Arthropods

supplementary material

Andrea Baucon^1,*, Steffen Trümper²,  Corrado Morelli³, Carlos Neto de Carvalho^4,5, Ausonio Ronchi⁶, Lorenzo Marchetti⁷, Evelyn Kustatscher^{8, 9}

1 DISTAV, Università di Genova, Corso Europa, 26, 16132 Genova GE, Italy – Italy
2 Institute for Geology and Palaeontology, University of M¨unster, Corrensstraße 24, 48149 Münster,
Germany. – Germany
3 Servizio Geologico, Provincia Autonoma di Bolzano, Via Val d’Ega, 48, 39053 Cardano, Italy – Italy
4 Earth Surface Processes Group (RG2) – Instituto D. Luiz, Faculdade de Ciˆencias da Universidade de
Lisboa, 1749-016 Lisbon, Portugal – Portugal
5 Geology Office, Municipality of Idanha-a-Nova, Naturtejo UNESCO Global Geopark. Centro Cultural
Raiano, Av. Joaquim Morão, 6060-101 Idanha-a-Nova, Portugal. – Portugal
6 Museum für Naturkunde [Berlin] – Germany
7 Museum of Nature South Tyrol, Via Bottai 1, 39100 Bolzano, Italy – Italy
8 Department of Natural History, Tirolean State Museum, Krajnc-Straße 1, 6060 Hall in Tirol, Austria –
Austria

Locomotion of Ommatoiolus. S Portugal.

Abstract – The late Cisuralian continental deposits of the Southern Alps present a very sparse body fossil record, likely due to mostly subaerial conditions hindering fossilization. However, the ichnological record provides crucial insights into the biodiversity of this upper Paleozoic ecosystem. Notably, paired hyporelief trace fossils, attributed to the ichnogenus Diplopodichnus, are abundant in the volcanically-influenced basins of the Southern Alps, specifically the Monte Luco and Collio Basin. These traces, characterized by straight paired ridges in convex hyporelief, suggest arthropod locomotion on wet substrates. Our study distinguishes two morphotypes of these trace fossils. In both basins, smaller traces with ridges 1 mm wide or less, spaced 10-40 mm apart, frequently co-occur with tetrapod tracks, stromatolites and microbially-induced sedimentary structures (gas domes, wrinkle marks). The association with microbial mats suggests that the preservation of metazoan traces may have been facilitated by microbial activity.  It also raises the possibility of the metazoan tracemakers grazing on the mats. The presence of tetrapod tracks indicates a subaerial habitat, supporting the hypothesis of millipede-like tracemakers and paralleling known arthropleurid-eryopid ecological associations. The larger morphotype, found only in the Collio Basin, comprises parallel ridges 3 mm wide with an 8 cm spacing. Recovered from a loose block, its palaeoenvironmental context suggests a continental setting, though the precise substrate conditions (subaerial or subaqueous) remain uncertain. The latter morphotype represents the largest known example of Diplopodichnus from the Permian of the Southern Alps. Its size suggests compatibility with arthropleurid tracemakers, although the possibility of other producers cannot be entirely ruled out. If this attribution to a millipede-like tracemaker is confirmed, it would represent the largest known from the Permian of the Southern Alps. Our results underscore the value of ichnological evidence in reconstructing Cisuralian ecosystems and highlights the role of microbial mats in trace fossil preservation. Future research should aim to verify the potential arthropleurid origin of these traces, as they may constitute one of the youngest records of this group, which is believed to have persisted only until the wet phase of the Sakmarian.