Ancient giant amphibian that lived 250 million years ago, swam like modern crocodiles

The researchers examined seven body impressions that revealed the animal's resting position as well as the number of tail marks that suggested swimming movement. The team surmised that one or two creatures were swimming from one resting spot to another, possibly searching for food.

The examination of these impressions resulted in the identification of this species. Several characteristics led them to believe that the creatures resembled crocodiles or giant salamanders. 

The first clue was derived from the curved shape of the tail marks. This means that animals used to set in motion through the help of continuous side-to-side tail motions, just like modern crocodiles and salamanders. Another characteristic suggests that they tucked their legs against their bodies while swimming, which is also similar to modern crocodiles.

The authors concluded with a statement: “The findings of the study are significant because they help to fill in gaps in our knowledge of these ancient animals. The remarkable tracks and traces preserved on the Dave Green palaeosurface are a window onto the shoreline of the Karoo Sea roughly 255 million years ago, and provide direct evidence of how these animals moved and interacted with their environment.” 

The findings can be accessed in the journal PLOS One.

Study abstract:

Large-bodied temnospondyl amphibians were the dominant predators in non-marine aquatic ecosystems from the Carboniferous to the Middle Triassic. In the Permian-aged lower Beaufort Group of the main Karoo Basin, South Africa, temnospondyls are represented exclusively by the family Rhinesuchidae and are well-represented by body fossils, whereas trace fossils are scarce. Accordingly, most interpretations of the behavior of this family are based on skeletal morphology and histological data. Here we document the sedimentology and palaeontology of a late Permian palaeosurface situated immediately below the palaeoshoreline of the Ecca Sea (transition from the Ecca Group to the Beaufort Group) near the town of Estcourt in KwaZulu-Natal Province. The surface preserves numerous ichnofossils, including tetrapod footprints and fish swim-trails, but most striking are seven body impressions and associated swim trails that we attribute to a medium-sized (~1.9 m long) rhinesuchid temnospondyl. These provide valuable insight into the behavior of these animals. The sinuous shape of some of the traces suggest that the tracemaker swam with continuous sub-undulatory propulsion of the tail.