The study carried out by a team of researchers from the Institut Català de Paleontologia Miquel Crusafont, the Institute for Evolutionary Studies of the University of the Witwatersrand, the Swedish Museum of Natural History in Stockholm and the Natural History Museum in London analyzed trace fossils located in the paleosurface known as the "Dave Green palaeosurface", located near the town of Estcourt in the province of KwaZulu-Natal (South Africa).
360o image of the Dave Green Paleosurface (Credit: David Groenewald)
The rocks comprising this ancient surface were deposited as sediment on a sandy tidal flat or lagoon floor and preserve numerous fossil trackways, including footprints made by four-legged animals and fish swim-trails. Most striking are seven body impressions and associated swim trails that the researchers attribute to a medium-sized (~1.9 m long) rhinesuchid amphibian. This remarkably well-preserved ancient surface is situated immediately below the transition from the Ecca Group to the Beaufort Group of the Karoo Supergroup and marks the shoreline of the ancient Karoo Sea – an inland sea that covered much of South Africa between 300 and 255 million years ago.
Rhinesuchids (family Rhinesuchidae) were a successful group of early amphibians and are well represented by body fossils from rocks of the Beaufort Group in the main Karoo Basin of South Africa. Rhinesuchids were typically big, with the largest species, Uranocentrodon senekalensis, being up to 3 m long. Trace fossils attributed to these animals are, however, not so common. Because of this, most interpretations of rhinesuchid behaviour are based on skeletal morphology and histological data.
Oblique field photographs of the six best preserved large impressions from the Dave Green palaeosurface. (Credit: David P. Groenewald)
“By utilizing digital recording methodologies, including 3D surface scanning and drone photography, we were able to accurately document the surface in high detail", says study co-author Dr Ashley Krüger. The team produced high-resolution 3D models of the best-preserved body impressions on the surface, which were used to obtain measurements and serve as a record of the footprints for future studies. The preserved impressions support interpretations that rhinesuchid amphibians held their legs tucked in next to the body while swimming and the sinuous shape of some of the swim traces suggests that the tracemaker swam with continuous sub-undulatory propulsion of the tail - similar to the way that extant crocodiles and salamanders swim.
The impressions also provide evidence that rhinesuchids engaged in bottom walking behaviour. “The findings of the study are significant because they help to fill in gaps in our knowledge of these ancient animals. The fossil trackways preserved on the Dave Green palaeosurface provide direct evidence of how these animals moved and interacted with their environment,” explains lead author Dr David Groenewald, now based at the Institut Català de Palaeontologia Miquel Crusafont in Barcelona, Spain.
“The rocks of the Karoo Supergroup of South Africa preserve one of the most complete records of life on earth between 300 and 180 million years ago. In addition to its remarkable scientific contribution, this study also demonstrates how important palaeontological discoveries are often made by curious people bringing their findings to the attention of palaeontologists,” says study co-author Prof Bruce Rubidge.
Comparison of Impression 2 from the palaeosurface (A) with a present-day body impression and trail of Alligator mississippiensis on the foreshore at St. Catherines Island, Georgia, United States (B). C) A rhinesuchid amphibian is probably the tracemaker. Scale bar = 30 cm (A and B).
Credit: David P. Groenewald. Photograph in B courtesy of St. Catherines Island Sea Turtle Program, Gale A. Bishop.
Support for the study was provided by the National Research Foundation (NRF) and its African Origins Platform; GENUS: DSI-NRF Centre of Excellence in Palaeosciences; the Palaeontological Scientific Trust (PAST); the Marie Skłodowska-Curie actions of the European Union’s Horizon Europe research and innovation programme; Consolidated Research Group 2021 SGR 01184 and the CERCA Programme of the Generalitat de Catalunya, Spain.
Article reference:
- Groenewald, D. P., Krüger, A., Day, M. O., Penn-Clarke, C. R., Hancox, P. J. & Rubidge, B. S. (2023). Unique trackway on Permian Karoo shoreline provides evidence of temnospondyl locomotory behaviour. PLOS ONE 18, e0282354. https://doi.org/10.1371/journal.pone.028235
