Australian researchers identified a new species of marsupial lion that roamed the rainforests of northern Australia 25 million years ago.
With a weight of just over 22 kg and a flat, flattened head, the new species, called Wakaleo schouteni after the illustrator and paleoartist Peter Schouten, is the fifth known species of marsupial lion size of a dog discovered in Riversleigh, located inside the Boodjamulla National Park, near the border between Queensland and the Northern Territory.
The formal announcement of the discovery, made in the Journal of Systematic Paleontology on Thursday, followed two decades of careful checks and cross references with fragments of other marsupial lions scattered throughout Australia.
The first piece of the puzzle was discovered by an enthusiastic volunteer in the 1980s, who saw some worn bones and teeth protruding from the rocks in a steep ravine in Riversleigh.
Paleontologists later discovered a skull, which was divided into two halves, and fragments of the postcranial skeleton – the humerus, the sacrum and some bones of the hand.
The lead author, Dr. Anna Gillespie, who started working on fossils as part of her doctorate at the University of New South Wales in the 1990s, worked on the back half of the skull when she received a call from a laboratory in Mt Isa. Both parts of the skull were found in Riversleigh, a fossil-rich limestone deposit that received the Unesco world heritage list in 1994.
It is unique in Australia for capturing a wide range of fossils dating from nine to 24 millions of years, allowing paleontologists to see the evolutionary history of certain species.
"[The lab] contacted me and said: 'We have the front half of a marsupial lion & # 39; and I said:' Well, I've already recovered ', and It was from the same place, and they sent it to me, and here I combined very well, "Gillespie told Guardian Australia. "That's the best specimen we have in reality, this beautiful skull."
The skull placed the animal in the family Wakaleo a primitive ancestor of the largest known carnivorous marsupial, 130kg Thylacoleo carnifex hunting megafauna between 1.9m and 30,000 years ago.
Most of the fossils were found in an area of limestone dating from the early Miocene, while others are believed to date from the late Oligocene, placing the animal time on earth between 18 million and 29 million years ago.
It is believed to be a contemporary of Priscileo pitikantensis a slightly smaller marsupial lion discovered at Lake Pitikanta, near Lake Eyre, in the remote south of Australia in 1961. The similarities between the two species saw the subsequent reclassification as Wakaleo pitikantensis .
Gillespie said the difference between the two could be due to differences in habitat or geographic isolation. It is also possible pitikantensis is a little older. The fossils of the three previously discovered Wakaleo suggest that each iteration of the carnivores was larger than the previous one.
Gillespie has not found enough examples of W. Schouteni & # 39; s arm and leg bones to be sure, but said the fossils of other animals preserved at his side suggests he may have carried an existence of tree climbing, running trunks with the help of opposable koala-type thumbs.
The bones of the arms collected so far suggest "a fairly sturdy shoulder, halfway between the koala and an opossum," he said.
"The diversity of mammalian faunas in Riversleigh sites indicates that it is likely that the environment up there at the end of the Oligocene was covered with forests, probably with open forests, but if we go into the early Miocene, the climate Australia became warmer and wetter and we can also see in Riversleigh that diversity is increasing again, so it seems that the forest is more closed, maybe possibly tropical rainforest, "said Gillespie. "Most likely, this animal would run after its prey, climb the trees and cross the treetops."
Its size, approximately that of a border collie, would have lent itself to an arboreal existence.
"They were not heavy animals, they could have easily sneaked trees after their prey," Gillespie said.
Riversleigh caves and limestone ridges, which continuously open new sinkholes and dissolve into puddles, trapping and preserving new fossils for scientists to study for another 100,000 years, can still provide more information.
"We're still looking for more fragments to answer more questions," Gillespie said. "Everyone else gets excited when they find skulls and teeth, I get excited when I find the bones of the limbs because I really like to fit these animals into their environments and see how they actually live."
Schouten, a highly respected illustrator whose imagination has shaped most of the prehistoric animals found in Riversleigh, said he was "stupefied" that a species bore his name.
"After scribbling what I love doing for the past 40 years, it's kind of weird to realize that people have noticed it," he told Guardian Australia. "It is a great honor to be recognized by my companions when I have a species that bears my name, and what species! I would have been happy with a humble nematode, but a marsupial lion … wow!"