London, Jan 22 : The discovery of 100 million year old fossilized jawbones of a platypus like animal suggests that egg-laying mammals such as the platypus might have evolved more slowly than other mammals.
According to a report in Nature News, the fossil found in Australia, is of an ancient creature called the Teinolophos, which lived in Australia more than 100 million years back.
Researchers have wondered whether this creature might be the ancestor of the platypus or spiny anteaters called echidnas, which are both egg-laying mammals that together come under a group of species called monotremes.
From examinations of Teinolophos skeletons, it was unclear whether the creature was a platypus or some general monotreme ancestor. So, Timothy Rowe of the University of Texas in Austin and his colleagues put three of the skulls through high-resolution X-ray tomography scans to investigate.
The scans revealed an enlarged canal that runs through the jaw, the shape and size of which is indicative of platypuses but not echidnas.
In modern animals, this canal supplies a platypus's sensitive bill with nerves and blood. Examinations of the animals' teeth likewise showed features common in platypuses but not echidnas.
That suggests that the split between these two groups happened before this creature came into existence, more than 100 million years ago.
This further indicates that monotrmes might have had a slow evolutionary history.
Though it's unclear that what exactly put the breaks on monotreme evolution, according to Rowe, monotremes generally have slow metabolisms and long generation times, both of which could theoretically slow the rate of evolutionary change.
Another factor that might have contributed to the slowing down of the evolutionary process of the monotremes is that if they were very well suited to their ecological niche, this would also be expected to have reduced the selective pressure to change.
According to Rowe, the creatures probably didn't need to evolve because their hunting abilities were so fine-tuned: the platypus bill is laced with highly sensitive nerve endings for detecting electrical signals emitted by prey.
But, some experts are against the notion that the Teinolophos might be the ancestor of the platypus.
"I'm not convinced it's a platypus," said David Wake, an evolutionary biologist at the University of California, Berkeley. "If you have to put it somewhere, you have to put it with a platypus, but we don't know anything about all the other ancient monotremes that once existed," he added.