COSMOS MAGAZINE
A 106-million-year-old fossil has flipped the script on monotreme evolution, revealing that echidnas and platypuses may share a water-dwelling ancestor with surprising traits still seen today.
The upper arm bone fossil belonging to the extinct monotreme Kryoryctes cadburyi.
Platypus in Queensland, Australia. Credit: Jamie Lamb elusive-images.co.uk/Getty Images
Platypus and echidnas are the only surviving members of the monotreme family.
This includes the only mammals to lay eggs rather than giving birth to live young. For this reason, they are considered relics of early mammal evolution.
Fossils of monotremes have been found in South America and palaeontologists believe they also existed in other southern continents and areas like Antarctica, New Zealand and Africa. Today, monotremes only live in Australia and New Guinea.
Platypus are one of two living species of monotreme. Credit: Robin Smith/Getty Images
Scientists once thought echidnas came from land animals, but new research shows their ancestor may have been semiaquatic, just like the platypus.
An artist’s impression of Kryoryctes. Credit: Peter Schouten.
CT scans of the ancient arm bone show it had dense, heavy bones — like modern diving mammals — suggesting it helped the animal sink and swim underwater.
An Australian platypus, eating a worm which may contain significant quantities of pharmaceutical products. Credit: John Carnemolla/ Getty Images
Traits like diving reflexes and backward feet in both echidnas and platypuses now make more sense — pointing to a shared water-loving ancestor who later walked back onto land.