A close-up of the skull of an adult P. trigoniceps reveals the robust interlocking teeth and the characteristic head flange that projects from the back of the skull. Arrows indicate tooth puncture marks, possibly made during territorial fighting.Credit: Roger Smith
Hundreds of curled-up fossils of a small burrowing reptile that lived in the lowlands of the ancient supercontinent of Gondwana some 250 million years ago, have been discovered in South Africa.
The research, published in Palaeo1, showed the skeletons are all the same reptile species, Procolophon trigoniceps, and they include both adults and juveniles.
Roger Smith, a professor at the Evolutionary Studies Institute, University of the Witwatersrand, who led the study, says: “Scratch marks on the burrow walls and floor match the front feet of Procolophon so we are confident that adults excavated underground tunnels sloping down about 35 degrees to about 1 m below the surface”.
The animals excavated several burrows in the same area, forming what seems like a colony.
Procolophon had teeth adapted to eating tough vegetation and possibly crustaceans, and would probably have foraged on the surface during the cooler times of day, staying underground through the heat of the day.
“It is more likely that they died they died from temperature stresses than starvation. We are not sure whether they died from overheating or dehydration or from prolonged cold,” says Smith.
The ability of tetrapods to burrow contributed significantly to their survivability under these conditions. Burrows create stable microclimates, with constant humidity and cooler temperatures, where these animals could survive.
“The wider ramifications of these findings,” said Derik Wolvaardt, a research associate in paleontology at the Iziko South African Museum, “are that we can now push the origins of communal living amongst land-living reptiles further back in time. Our study now provides convincing evidence dating back 247 million years ago.”
The previously oldest convincing evidence of communal living2 in terrestrial tetrapods is from about 193 million years ago. It shows herding, communal nesting, and possibly even social structuring by age group for the dinosaur, Mussaurus.
The new research suggests that the driving forces of this behaviour, which is common for reptiles of dryland ecosystems today, were the dramatic ‘drought and deluge’ climatic fluctuations that affected the entire globe in the immediate aftermath of the End-Permian mass extinction.
“Drought and deluge” refers to a pattern of extreme climate variability, where long periods of very dry conditions are suddenly followed by intense rainfall and flooding. This alternating cycle creates a harsh and unstable environment, particularly challenging to survive or recover in.
