Contributions of Southern South America to Vertebrate Paleontology

BAEZ, A. M.; BASSO, N. G.

The Earliest Known Frogs of the Jurassic of South America: Review and Cladistic Appraisal of their Relationships

Verlag Dr. Friedrich Pfeil

Lugar: Munchen; Año: 2006; p. 131 - 158

The earliest records of frogs in South America, which are also some of the oldest known occurrences  of this group of amphibians, are from the Jurassic of the most southern part of this continent. The Liassic Vieraella herbstii REIG and the Callovian-Oxfordian Notobatrachus degiustoi REIG have been considered to be allied with the most primitive living anurans Ascaphus and Leiopelma; however, most of the characters that these taxa share are plesiomorphic. A reinterpretation of these fossil taxa, based on the study of high-fidelity casts of published, as well as recently collected, material is presented. Interesting features overlooked in previous studies include the presence of ten presacral vertebrae, the extensive posterior body of parasphenoid and the conspicuous vomers of Vieraella, and the presence of a parahyoid bone and the peculiar structure of the vertebrae of Notobatrachus. Based on this new information, a phylogenetic analysis was designed to address the problem of the cladistic relationships of both taxa. Cladistic analysis was performed using Hennig86 software, version 1.5. Fifty equally weighted characters, binary as well as multistate, and representing all of the major structural regions of the skeleton, were used. The living anuran taxa Alytes, Ascaphus, Bombina, Discoglossus, and Leiopelma were also included in the ingroup. Vieraella is the most basal known member of Salientia, except the Early Triassic Triadobatrachus from Madagascar, in the possession of a higher number of presacral vertebrae. However, several character states of Vieraella remain in doubt owing to the poor preservation of the single known representative; thus a high degree of uncertainty remains with respect to its phylogenetic position. The bizarre Notobatrachus is the sister taxon of the crown group Anura as it possesses the plesiomorphic state of several anuran synapomorphies. This study does not support neither a close relationship between these two fossil taxa nor their alliance with Ascaphus and/or Leiopelma, as proposed previously. Early vicariant events in salientian history might have been related to continental rifting, rather to actual break up of the Paleozoic-Early Mesozoic Pangaea.