Australia\u2019s burrowing echidna evolved from a water-dwelling ancestor in an \u201cextremely rare\u201d biological event, scientists said in a new study of the peculiar egg-laying mammals.<\/p>\n
With powerful digging claws, protective spikes and highly sensitive beaks, echidnas are well suited to a life shuffling through the forest undergrowth. But a team of Australian and international scientists believe many of the echidna\u2019s unusual traits were first developed millions of years ago when its ancestors splashed through the water.<\/p>\n
\u201cWe\u2019re talking about a semiaquatic mammal that gave up the water for a terrestrial existence,\u201d said Suzanne Hand, a palaeontologist from the University of New South Wales.<\/p>\n
\u201cWhile that would be an extremely rare event, we think that\u2019s what happened with echidnas.\u201d<\/p>\n
Echidnas and another Australian oddity \u2013 the semi-aquatic platypus \u2013 are believed to have evolved from a common ancestor called Kryoryctes cadburyi that lived in Australia more than 100m years ago.<\/p>\n
Researchers studied the single known bone fragment left by this ancestor which was discovered among a trove of fossils at Dinosaur Cove in southern Australia 30 years ago.<\/p>\n
Platypus bones were similar to this ancient ancestor, Hand said, with a thick and heavy structure that provided ballast for diving. Echidnas, by comparison, had very thin bone walls that made it easier to walk on land.<\/p>\n
This indicated echidnas were descended from a water-dwelling ancestor but had evolved to live on land, the research found.<\/p>\n
It was far more common for prehistoric mammals to go from land to water, Hand said, pointing towards seals, whales, dolphins and dugongs.<\/p>\n
The researchers said these findings appeared to be supported by other echidna traits. Echidnas have backward-facing hind feet that help them shift mounds of soil when burrowing. These feet may have first developed as rudders helping the echidna\u2019s ancestor navigate fast-moving waterways, Hand said.<\/p>\n
Echidnas also have a \u201cdiving reflex\u201d when submerged in water, which tells their body to conserve oxygen, helping them hold their breath for longer.<\/p>\n
Echidnas and platypus are monotremes, a rare group of mammals that lay eggs instead of live young.<\/p>\n
\u201cWe\u2019re hoping we\u2019ll discover other ancestral monotremes that will help unravel the early history of this most fascinating group of mammals,\u201d said Michael Archer, a co-author of the study.<\/p>\n
The research was published in peer-reviewed journal PNAS.<\/p>\n