Raederichnus dondasi a new trace fossil from the Early Paleozoic of Argentina reveals shoaling behavior in early fishes

HALPERN, KAREN; GOUIRIC CAVALLI, S.; MATIAS TAGLIORETTI; FARENGA, MARCELO; FERNANDO SCAGLIA; CALVO-MARCILESE, LYDIA; DEL RÍO, JULIO

PALAIOS

SEPM-SOC SEDIMENTARY GEOLOGY

Lugar: Lawrence; Año: 2022

0883-1351

Possibly being overlooked, vertebrate traces are scarce worldwide in the Lower Paleozoic. Despite the abundance of vertebrate carcasses ?particularly those assigned to fishes? in the fossil record, the literature rarely mentions them as trace producers. Based on the study of more than 100 big, shallow, and drop-shaped imprints ?several aligned and even a few overlapped? from Ordovician-Silurian outcrops of western- Gondwana (southeastern Argentina), here we report the oldest shoaling behavior. To understand the nature of the recorded behavior, we considered analog (vertebrate and invertebrate) extant and extinct forms. We also compare and discuss the superficial similarities that recall some invertebrate traces particularly Selenichnites isp. We erected a new ichnotaxon, Paleopiscichnus dondasi isp. nov. The comprehensive assessment of the sites allowed us to recognize the putative presence of ?Psammichnites, previously unknown for the area, and Herradurichnus scagliai. All studied traces appear preserved in three-dimensional dunes, developed in a tide-dominated shallow marine environment. The presence of microbially induced sedimentary structures presumably enhanced the preservation of the traces. The new bedding surfaces reported show dominance of Paleopiscichnus dondasi isp. nov. traces and low ichnodiversity. Due to the morphological resemblance and paleoecological preferences, we interpret that each trace might have originated in response to a fish?s resting behavior. Finally, we suggest that fish shoaling is related to feeding or breeding on the shallow bottom marine surface.