Scientists found a fossilized amphibian and a mammal that had been trapped in their shared burrow by a flash flood.
Researchers discovered the strange pair when using synchronized imaging to scan a fossilized burrow located in the Karoo Basin of South Africa, according to a University of the Witwatersrand press release.
The amphibian Broomistega and the mammal-like reptile (an early mammal) Thrinaxodon, were cohabiting a burrow 250 million years ago, following the Permo-Triassic extinction.
The researchers believe the amphibian was suffering from broken ribs, and may have crawled into the mammal's burrow for protection. Research suggest the Thrinaxodon used burrowing behavior coupled with periods of dormancy, called aestivation, to survive the mass extinction.
The discovery marks the first known relationship between these two totally unrelated creatures.
"While discovering the results we were amazed by the quality of the images", said lead author Dr. Vincent Fernandez, "but the real excitement came when we discovered a second set of teeth completely different from that of the mammal-like reptile. It was really something else."
During the Triasic period, when the creatures lived, the area which is now South Africa was experiencing intense warming characterized my heavy monsoon weather. The number of fossils found in similar situations suggest mammals, and mammal-like reptiles, used burrowing as a survival technique.
Earlier this year scientists decided to examine these burrows using X-ray technology which allowed them to look inside the sedimentary rock without damaging the fossils. They selected two burrows as the subjects for their study. They were surprised to find the two creatures present in the same burrow.
"Burrow-sharing by different species exists in the modern world, but it corresponds to a specific pattern," Fernandez said. "For example, a small visitor is not going to disturb the host. A large visitor can be accepted by the host if it provides some help, like predator vigilance. But neither of these patterns corresponds to what we have discovered in this fossilized burrow."
One possible explanation for the cohabitation could have been one creature turning the other into its lunch, but this didn't seem quite right either.
"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 who participated in the study.
The studies showed the amphibian's broken ribs were a result of one massive trauma, and it had sustained the injuries some time before its death because they were already starting to heal.
The scientists eventually concluded the amphibian crawled into the burrow because of its injury, and the mammal was in a state of aestivation so it did not chase the visitor out.
"Thanks to the unique possibilities for high quality imaging of fossils developed during the last decade at the [European Synchrotron Radiation Facility], these unique specimens remain untouched, protected by their mineral matrix," said Paul Tafforeau, of the ESRF who was a part of the study. "Who knows what kind of information we'll be able to obtain from them in the future and which would have been completely lost if the specimen had been prepared out of its burrow cast?"
