Quaternary fossil diversity of stingrays (Chondrichthyes: Myliobatiformes) from the eastern coast of South America, Brazil, southwestern Atlantic

Abstract

Sharks, rays, and chimeras have a limited fossil record compared to other taxa due to their predominantly cartilaginous skeletal structure. Fossilization tends to preserve anatomic structures such as teeth, scales, cephalic and caudal fins, and other fins. The Myliobatiformes order, derived from rays, is characterized by viviparity and distinctive serrated stings, with some species exhibiting hexagonal dental plates. These marine organisms inhabit coastal zones globally. This study aims to enhance understanding of Quaternary biodiversity and paleoecology in southern Brazil, focusing on fossils from the Myliobatiformes order, specifically dental plates and stings. Material from biodetrital deposits at Concheiros and Hermenegildo beaches in Santa Vitória do Palmar, Rio Grande do Sul, Brazil, were analyzed. Six taxa were identified from fossil teeth, including Myliobatis ridens, Myliobatis freminvillei, Myliobatis goodei, and Myliobatis sp. (Morphotypes 1 and 2), marking their first Pleistocene fossil record in Brazil. Most teeth couldn't be classified at the species level, but genera were discerned. Fossil stings were described, possibly associated with Myliobatiformes. Results revealed notable differences between identified fossil taxa and their modern counterparts in the western Atlantic Ocean, currently considered common. M. ridens was the most frequent species in the fossil samples, followed by M. freminvillei, with fewer records for M. goodei. Conversely, the current scenario shows M. goodei as the most abundant, followed by M. freminvillei, while M. ridens is Critically Endangered. This investigation expands knowledge of fossil species on the southern Brazilian coast, confirming the presence of M. ridens, M. freminvillei, and M. goodei during the Quaternary.