New evidence from the Lower Jurassic of Patagonia sheds light on the history of some of the earliest known frogs

BÁEZ, ANA M.; GÓMEZ, RAÚL O.

Haarlem

Congreso; XIV Annual Meeting European Association of Vertebrate Paleontologists; 2016

Teylers Museum

The early evolution of frogs is still poorly documented in the fossil record, persisting a 50 My gap without any fossil find between those of the oldest known salientians and the first frogs. According to previous information, the oldest known frog from the southern continents was Vieraella herbstii from supposedly Toarcian?Aalenian beds of southern Patagonia, whereas this record was followed by those of Notobatrachus degiustoi and N. reigi, both of putative Callovian?Oxfordian age, also from Patagonia. New discoveries from the Lower Jurassic of Patagonia coupled with a better resolution of the chronological framework of the frog-bearing levels indicate that the diversification of frogs in this world region took place earlier than previously thought. In the last decade, paleontological prospection of the lower Cañadón Asfalto Formation in the area of Cerro Cóndor, central Patagonia, has led to the discovery of many Notobatrachus-like frog remains in different localities. These fossiliferous levels transitionally follow the Lonco Trapial deposits related to the volcanism that affected this region during the Early Jurassic. Recent U-Pb radioisotopic dating places at least some of these levels in the middle-late Toarcian, including those bearing N. reigi. It is noteworthy that this age interval is close to the recent Pliensbachian?Toarcian U-Pb dating of the Kayenta Formation beds that yielded Prosalirus bitis, the supposedly oldest known frog. The new high-precision geochronology of the Patagonian volcanism linked to the western Gondwana breakup, together with paleontological studies in progress, reveals the persistence of the lineage represented by Notobatrachus throughout nearly 20 My in water bodies associated with volcanic environments.