Fossil fishes and anurans from the Miocene of Rio Chico and Cerro Zeballos, Chubut Province, Argentina.

Federico L Agnolín,Laureano R Gonzalez Ruiz,Sergio Bogan

doi:10.1590/0001-3765202120191438

Abstract

The fossil record of freshwater fishes and anurans from the Miocene in Patagonia is relatively patchy, a large number of specimens remaining undescribed. The aim of the present contribution is to describe a fossil association of percomorphacean fishes and calyptocephalellid anurans from the early to late Miocene Collón Curá Formation, at Chubut province, Patagonia, Argentina. In spite of being represented by several specimens, both anurans and fishes show a very low taxonomic diversity. This pattern matches with other fossil sites from the Cenozoic of Patagonia, as well as with the extant Patagonian batrachofaunas and ichthyofaunas. The fossil record of frogs and fishes in Patagonia is represented by few lineages that have a large evolutionary history in the area, and occasionally can be traced up to the Late Mesozoic.

Highlights

Fishes and anurans are intimately related with the evolution of freshwater bodies
From the Ñirihuau Formation at Río Negro and Chubut provinces indeterminate teleosts, percichthyids and atherinopsids were reported (Feruglio 1949, Dessanti 1972, Bocchino 1964, 1971, Pascual et al 1984), whereas percichthyids were recorded from Collón Curá Formation at Río Negro province (Casamiquela 1963)
During the Tertiary, percichthyidlike taxa are the most abundant fishes recovered in Patagonian fossil sites (e.g., Cañadón Hondo, Puesto Galván, Cerro David), whereas other taxa as atheriniforms, siluriforms and osteoglossiforms are known from few fossiliferous sites (Bogan et al 2010, Azpelicueta & Cione 2011)

Summary

INTRODUCTION

Fishes and anurans are intimately related with the evolution of freshwater bodies. As a result, there is often a close match between the evolutionary history of river basins and the fish lineages that inhabit them. The specimens here described share a combination of characters that are typical of the Percomorphacea clade, including presence of spinose rays in dorsal and anal fins, first precaudal vertebra with two articular surfaces indicating an autogenous neural arch, presence of wide trabeculae on lateral surface of vertebral centra, morphology of the ascending process of premaxilla, edentulous maxilla, and serrated posterior margin of the preopercle (see Johnson 1993, Gayet & Meunier 1998, Agnolín 2012). When compared with South American percichthyids of the genera Percichthys, Santosius and Plesiopercichthys (see Arratia & Quezada-Romegialli 2019), the specimens here reported show some differences, including symphyseal region of the dentary composed by two bumps separated by a longitudinal groove, premaxilla with a wide and thickened ascending process, and hyperostosic and enlarged first pterygiophore of the dorsal fin Such features are unknown in any known extinct. Because of its fragmentary nature, the specimen is here considered as an indeterminate calyptocephalellid

DISCUSSION

CONCLUSIONS