Anurans from the Early–Middle Miocene Santa Cruz Formation at Río Chalía (Patagonia, Argentina), and a revision of the fossil Calyptocephalellidae (Anura: Australobatrachia)

Abstract

A large number of vertebrate fossils has been collected from the outcrops of the early–middle Miocene Santa Cruz Formation (SCF) along the Río Chalía in southern Patagonia, Argentina. The analysis of the anuran components reveals the coexistence of two Calyptocephalella species as the only frog inhabitants of the Santacrucian fauna, one of them especially large and abundant. Amongst the hundreds of anuran fossil remains, many provided relevant anatomical data to identify new characters to emend the diagnosis of Calyptocephalella, and to reconsider the taxonomic status of the largely controversial “Gigantobatrachus” parodii. The latter is herein definitively recognised as part of Calyptocephalella, C. parodii stat. rev. et nov. comb. Also, a new genus, Xerocephalella nov. gen., is erected to allocate two species that were formerly included within Calyptocephalella but lack some characters of the temporal region in the skull, herein included in the diagnosis of this genus. The SCF was deposited during an interval that spans a climatic episode, the Miocene Climatic Optimum, and the fossil record reflects the faunal variations associated to climatic/environmental changes that occurred during this period. The sympatric presence of the anurans Calyptocephalella parodii stat. rev. et nov. comb. and C. cf. C. canqueli at the lower levels of the unit and the presence of only one of them at the uppermost levels suggests a declining trend of the lineage along the Miocene, a decline that resulted in the extinction of Calyptocephalella east from the Andes.