SYDNEY, March 29 (Xinhua) -- The origins of two of the world's most distinctive animals, echidnas and platypuses, have been uncovered by an international research team led by Australian scientists.
The research, published in Alcheringa, an Australasian Journal of Paleontology, and revealed on Monday, showed the animals' ancestors date back 130 million years, to an era when they roamed through icy forests of regions of Australia, which was then close to the South Pole.
"This research reveals their unique origin story and helps us understand how they came to live in Australia in all shapes and sizes throughout the fossil record," mammalogist Tim Flannery said of the world's only surviving monotremes, which are egg-laying mammals.
The research team, which included scientists from Museums Victoria, Monash University, and Swinburne University in Melbourne and the Smithsonian Institution from the United States, examined every known significant monotreme fossil.
Among the fragments from the prehistoric polar forests were the remains of the oldest and smallest monotreme, Teinolophos trusleri, which has now been classified in a new mammalian family.
"This is an incredible survival adaptation for this mini monotreme, which we estimate had a body mass of about 40 g - roughly the weight of a slice of bread," said Flannery.
"Imagine it using its snout to plunge into moss and snow to find food it can't see and hasn't yet touched."
At the other end of the scale, they looked at fossils of the largest ever egg-laying mammal, a gigantic echidna from Western Australia, for which a new genus, Murrayglossus, has been named.
"Weighing 30 kg, roughly the size of a wombat, this massive monotreme would have been many times the size of modern Australian echidnas," said Australian Museum chief scientist Kristofer Helgen.
The researchers believe the fossils of the oldest monotremes indicate the animals were suited exclusively to a polar climate, which restricted them from spreading elsewhere.
According to Helgen, the research also sheds light onto the likely migration of echidnas from Papua New Guinea to Australia.
"Echidnas are found in the Australian fossil record going back only 2 million years," Helgen said. "Yet genetic studies indicate echidnas evolved from platypus-like ancestors tens of millions of years before that."
"We think echidnas originated on an island in what has now become part of New Guinea, and that they reached Australia during a period of faunal exchange around the onset of the Ice Ages."
Flannery, who is also one of Australia's best-known environmentalists, said although the research focused on the past, the researchers "also want to highlight the urgent need for protection of our modern platypuses and echidnas, which are under threat and in decline as a result of human-induced habitat degradation". ■