The discovery by South African scientists of a 250-million-year-old fossilised embrace between two animals, has been hailed as a world first.
The rain was pouring down as the skies opened up in the Karoo Basin 250-million years ago. An injured amphibian Broomistega, possibly hurt by the storm, crawled into a sleeping animal's burrow to shelter from the violent weather. It is suspected that the mammal-forerunner Thrinaxodon – which, from simulations resembles a furry Komodo dragon – was hibernating, although when done for short periods of time this is called aestivation.
Both animals died, and their fossilised embrace, discovered by South African scientists, marks a world first. The results were published in scientific journal PLOS ONE on Friday. The remains were analysed using the European Synchrotron Radiation Facility (ESRF).
Earlier this year, South Africa joined the ESRF as a full member. The synchrotron, based in Grenoble, France, emits X-rays around a circular tunnel the size of a stadium. The wavelengths of the beam are so small that they can get between atoms in a material, and scientists can characterise it on an atomic level. This means that it can analyse fossils without damaging them.
"While discovering the results, we were amazed by the quality of the images," said lead author Vincent Fernandez from Witwatersrand University. "But the real excitement came when we discovered a second set of teeth completely different from that of the mammal-like reptile."
They hypothesised a number of different scenarios that would result in this odd-couple embrace. "It's a fascinating scientific question: what caused the association of these two organisms in the burrow? One of the more obvious possibilities is a predator-prey interaction, but we inspected both skeletons looking for tooth marks or other evidence implying predation, ultimately finding no support for one having attempted to feed on the other," said Dr Kristian Carlson, another author on the paper who is based at Wits University.
The team finally concluded that "the mammal-like reptile, Thrinaxodon, was most probably aestivating in its burrow, a key adaptation response together with a burrowing behaviour which enabled our distant ancestors to survive the most dramatic mass extinction event. This state of torpor explains why the amphibian was not chased out of the burrow," said Professor Bruce Rubidge, co-author of the paper and also the director of the Centre for Excellence in Paleosciences based at Wits University.