Johannesburg - A team of scientists have found what they believe to be the oldest of odd animal couples: an amphibian and a mammal-like reptile that snuggled up in a fossilised burrow right here in South Africa – 250 million years ago.
It’s one of a number of fossilised burrows found in the Karoo Basin and analysed by a multinational team, including Wits University researchers.
In the study published last week in scientific journal PLoS ONE, the scientists describe how they believe the two small creatures came to be together.
It was 250 million years ago – the beginning of the Triassic Period, a time when all the modern continents were connected as Pangaea and South Africa and Antarctica touched.
The world had just undergone the Permo-Triassic extinction event, which killed off most land, sea and insect species.
To survive the harsh environment, the mammal-like reptile – Thrinaxodon – burrowed into the earth for safety. This isn’t new: scientists have found Thrinaxodon in fossilised burrows before.
But when they scanned the fossil with X-ray, the 3D images showed something more.
“While discovering the results, we were amazed by the quality of the images,” said the study’s lead author, Dr Vincent Fernandez, of Wits. “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.”
Thrinaxodon had made a friend: an amphibian – Broomistega.
The coupling defied the standards of modern burrow-sharing: neither animal was small enough not to disturb the other, nor big enough to provide some kind of protection.
The scans showed no tooth marks to suggest one of the animals was trying to feed on the other, and Thrinaxodon was curled up, like it was peacefully resting.
How had the pair come together?
The clue was in the bones.
Scans showed Broomistega had a number of broken ribs, the result of a “single, massive trauma”.
The bones were healing but, handicapped by the injury, the amphibian crawled into the burrow.
As for Thrinaxodon, the evidence points to what scientists call aestivation. It’s a period of animal dormancy, triggered by high, dry temperatures and little food – like the hot opposite of hibernation.
It explains the reptile’s sleeping shape, and also why it didn’t chase its new bed partner from the burrow.
When a flash flood hit, the two were fossilised together for a quarter of a billion years. - The Star