Deciphering myriapoda population dynamics during Gondwana deglaciation cycles through neoichnology

Abstract

In this work, we explore the biogenic structures generated by extant myriapods on the substrate surface to understand better the record of Diplichnites gouldi and other related traces in the topmost deposits of the Late Carboniferous Itararé Group (Paraná Basin, S Brazil) and the population dynamics of Myriapoda in an ancient glacial setting. Controlled neoichnological experiments involving substrate composition, plasticity, and moisture provided information about the morphometric traits and preservation potential of the crawling traces produced by Chilopoda and Diplopoda individuals. Morphometric (cluster) analysis using a sampling of 50 D. gouldi specimens provided information about size variability in these trackways in the studied deposits. The extant millipede and centipede individuals produced trackways like D. gouldi and trails similar to Diplopodichnus biformis. The millipedes also produced shallow furrows that fit in Cruziana problematica and traces that resemble a bass clef. These two morphologies are also present in the glacial trace fossil assemblage of the Itararé Group. A new ichnotaxon, Clavifasulcus jordii n. igen. et isp. was erected to characterize the trails that resemble a bass clef, and the neoichnological experiments allowed assuming them as a millipede's death march or pose. The morphometric analysis revealed seven different size classes among D. gouldi, coinciding with the number of myriapod's ontogenetic stages. Considering the very low diversity of myriapods in glacial settings, the population dynamics of extant myriapod in these environments, and the short colonization window represented by each rhythmite couplet, we consider that the different size classes found in D. gouldi in the topmost rhythmites of the Itararé Group rather represents ontogeny than a diversity of tracemakers.