Prehistoric fossils unlikely bedmates

John Harvey

THEY are the unlikeliest of “bed fellows”, particularly since they are more than 250 million years old, but that is ultimately what nature had in store for an amphibian and mammal forerunner, who shared a burrow in the Karoo Basin.

In a world first, scientists from the University of the Witwatersrand, Australia and France have discovered an unusual association between a mammal-like creature called Thrinaxodon and an amphibian called Broomistega, after uncovering a fossilised burrow.

While the burrow was already discovered in the 1970s, for the past two years scientists have been investigating a strange phenomenon that showed there were actually two fossilised animals lying side by side.

Scanning showed that the amphibian, which was suffering from broken ribs, crawled into a sleeping mammal’s shelter for protection. Researchers believe that short periods of dormancy called aestivation, in addition to burrowing behaviour, may have been a crucial adaptation allowing mammal ancestors to survive the extinction period.

The outcomes of this research resulted in a paper entitled, “Synchrotron reveals Early Triassic odd couple: injured amphibian and aestivating therapsid share burrow”, published in the scientific journal PLoS ONE at the weekend.

Wits researcher Dr Kristian Carlson, who worked on the project with colleague and head researcher Vincent Fernandez, said yesterday it was not until about two years ago that the association was made.

“When we noticed the skeletons we sent them off for testing, and this is what we came back with,” he said.

About 250 million years ago, the ecosystem was recovering from the Permo-Triassic mass extinction that wiped out most life on Earth.

In order to survive this harsh environment many animals developed a digging behaviour, attested by the numerous fossilised burrow casts discovered in the Karoo Basin.

“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,”

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