Comparisons of dental morphology in river stingrays (Chondrichthyes: Potamotrygonidae) with new fossils from the middle Eocene of Peruvian Amazonia rekindle debate on their evolution

Abstract

Endemic South American river stingrays (Potamotrygonidae), which include the most diversified living freshwater chondrichthyans, were conspicuously absent from pre-Neogene deposits in South America despite the fact that recent phylogenetic analyses strongly suggest an older origination for this clade. To date, the rare representatives of this family were mostly represented by ambiguous isolated remains. Here, we report 67 isolated fossil teeth of a new obligate freshwater dasyatoid (Potamotrygon ucayalensis nov. sp) from the fossiliferous level CTA-27 (Yahuarango Formation), near Contamana, in the Peruvian Amazonia. We assigned this sample to a new representative of Potamotrygon by comparison with numerous fresh jaws of living specimens of Potamotrygonidae, thus providing the first detailed review of dental morphology for this poorly understood clade. These new fossils fill a long stratigraphic gap by extending the family range down to the middle Eocene (~41 Mya). Moreover, the relative modernity and diversity in tooth morphology among Eocene freshwater stingrays (including Potamotrygon ucayalensis nov. sp. and coeval North American dasyatoids) indicate that the hypothetically marine ancestor of potamotrygonids probably invaded the rivers earlier than in the middle Eocene. The first potamotrygonids and affiliates were possibly more generalized and less endemic than now, which is consistent with an opportunistic filling of vacated ecospace.

A Miocene hyperdiverse crocodylian community reveals peculiar trophic dynamics in proto-Amazonian mega-wetlands

“…B 282: 20142490 corbulid-globidontan interaction [34]. Similar interactions are hypothesized for molluscs and durophagous freshwater stingrays, co-occurring in early Palaeogene deposits of both the Great Plains (Palaeocene) and Western Amazonia (Middle Eocene-onward) [35].…”

A Pliocene–Pleistocene continental biota from Venezuela

“…In non-cuspidate teeth, the crown looks wider than long, with both rounded and concave labial sides. We identify the presence of teeth with cuspidate (males) or non-cuspidate (females) crowns, as the sexual dimorphism in adult individuals of the freshwater stingray Potamotrygon (see Adnet et al 2014). With the exception of only two cuspidate teeth (Fig.…”

Contribution to the reappraisal of the mid Paleogene ichtyofauna of Western Africa with three new enigmatical elasmobranchs from Thanetian–Lutetian of Senegal

“…South American fossils of this subfamily drew particular attention this last decade (e.g. Brito and Deynat, 2004;Adnet et al, 2014;Chabain et al, 2017) with evidences that they were abundant in middle Eocene deposits of Peruvian Amazonia. In contrast, the living styracurines (amphi-American whipray) are less abundant.…”

“…Landini et al, 2017;Carrillo-Bricenio et al, 2014, 2018. However, the styracurines likely inhabited the Eastern Pacific-Caribbean zone since the middle Eocene, which corresponds to the oldest occurrence of their sister taxa, the potamotrygonins (Adnet et al, 2014). The attribution of Atlantitrygon to Styracurinae is based on the similar overall shape of the teeth and the presence of a displaced main cusp.…”