Small Amphibian and Reptile Footprints from the Permian Carapacha Basin, Argentina

Abstract

This paper contains a taxonomic study of the Permian tetrapod ichnofauna from the Carapacha Basin. Tetrapod traces are analyzed in their environmental context and compared with similar faunas from Europe and North America. This ichnofauna is particularly relevant because of the scarcity of Permian tetrapod tracks from South America and also of Permian tetrapod fossils from Argentina. Ephemeral fluvial and shallow lacustrine deposits compose the sedimentary succession of the basin, which is represented by the Carapacha Formation. Most of the tracks have been collected from the upper member of the formation (Urre-Lauquen Member), mainly from freshwater ephemeral lake deposits as well as from playa-lake mudflats. The deposits of this member have been attributed to the early Late Permian on the basis of a Glossopteris fossil flora. Ichnotaxonomic designations of tetrapod traces are made on the basis of morphologic features that reflect the anatomy of the producer and special attention has been paid to extramorphologic deformations observed in the track assemblage. A total of four footprint ichnotaxa have been recognized, namely Batrachichnus salamandroides (Geinitz, 1861), Hyloidichnus bifurcatus Gilmore, 1927, cf. Amphisauropus isp. and cf. Varanopus isp. These track taxa are associated with two forms of vertebrate swimming traces (Characichnos isp. and type A swimming trace) and a possible fish trail. Invertebrate trace fossils include abundant arthropod locomotion traces and Scoyenia isp. The ichnofauna is composed of six tetrapod ichnocoenoses that are dominated by tiny amphibian tracks attributed to Temnospondyli (Batrachichnus and type A swimming trace) and Seymouriamorpha (Amphisauropus), and also contain the footprints of small reptiles, mostly Captorhinomorpha and possibly Pelycosauria (Hyloidichnus and Varanopus). Even if the ichnofauna of the Carapacha Basin is slightly younger than typical examples from the literature of the Early Permian “red bed ichnofacies” (Hunt et al., 1995b), a comparison is made. However, further detailed case studies are needed to formally define this “red bed ichnofacies” and its prospective subdivisions.

Keywords:

• Permian
• Argentina
• Carapacha Basin
• lacustrine environment
• Batrachichnus
• Hyloidichnus
• Varanopus
• Amphisauropus
• Characichnos
• tetrapod swimming traces

ACKNOWLEDGEMENTS

This study started in 1993, after the authors met at the First Argentine Meeting of Ichnology, held at Santa Rosa, La Pampa province. The completion of the project was largely delayed because of the primary involvement of the first author with non-ichnological research projects. After many interchanges, the final agreement about the details of the paper was made during Bill Sarjeant's last visit to Santa Rosa in May 2000. Unfortunately, Bill could not read the manuscript, so the full responsibility remains with the first author. R. N. Melchor is indebted to H. Haubold for his invitation to attend the Workshop “Ichnofacies and Ichnotaxonomy of the terrestrial Permian” held in Germany in 1997, which was influential in his “vertebrate ichnologist career.” The workshop gave him the opportunity to revise abundant material of Permian footprints from Germany and to meet leading ichnologists from different countries. Special thanks to Thomas Martens (Museum der Natur, Gotha, Germany) for his hospitality during and after the workshop, to reviewers Robert Reynolds and Daniel Marty, and to Ichnos editor S. George Pemberton.