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Marsupial lions, kangaroos as tall as trucks and wombats the size of a rhinoceros roamed Australia's outback before being killed off by fires lit by invading humans, scientists said.
The giant animals lived in the arid Nullarbor Desert around 400,000 years ago, but died out around 50,000 years ago, relatively shortly after the arrival of human settlers, according to new fossil skeletons found in caves.
Fossilised remains were uncovered almost intact in a series of three deep caves in the centre of the Nullarbor Desert - east of the west coast city of Perth - in October 2002. "Three subsequent expeditions produced hundreds of fossils so well-preserved that they constitute a veritable "Rosetta Stone for Ice-Age Australia", expedition leader Gavin Prideaux said of the find, detailed in the latest edition of the journal Nature.
The team discovered 69 species of mammals, birds and reptiles, including eight new species of kangaroo, some standing up to three metres tall.
Protected from wind and rain, and undisturbed due to their remote location, the remains of the mega-beasts are in near-perfect condition, including the first-ever complete skeleton of a marsupial lion, Thylacoleo carnifex.
"Unwary animals bounding around, in the case of kangaroos, or running around, in the case of marsupial lions and wombats, fell down these holes, as presumably most were nocturnal. It's very difficult to see a small opening on a flat surface at night," Dr Prideaux said.
Research into the fossils challenges recent claims that Australia's megafauna were killed off by climate change, pointing the finger instead at fires, probably lit by the first human settlers.
The lands inhabited by the megafauna once supported flowers, tall trees and shrubs. But isotopes extracted from skeletal enamels show the climate was hot and arid, similar to today.
The plants, the scientists said, were highly sensitive to so-called fire-stick farming, where lands were deliberately cleared by fires to encourage regrowth.
"Australian megafauna could take all that nature could throw at them for half-a-million years, without succumbing," said Richard Roberts, a geochronologist at the University of Wollongong. "It was only when people arrived that they vanished."
In another scientific breakthrough, zoologists have discovered a new species of squirrel-like mammal, which they have described as a strikingly unusual creature, in the high mountains of Peru.
The nocturnal animal looks similar to a squirrel, and is about the same size, but DNA tests have shown that it is more closely related to a family of South American spiny rats whose fur bristles with spines.
The new species is a climbing rodent with strange-looking, long, dense fur, a broad head and thickly furred tail tipped with white. It also has a distinctive blackish crest of fur on its crown, nape and shoulders.
Scientists discovered the rodent during a field survey in 1999 of Peru's Manu National Park and Biosphere Reserve Mountains on the lush eastern slopes of the Andes in southern Peru, which is one of the richest regions in the world for wildlife.
However, its formal scientific description and official naming has only now been made public in the journal Mastozoologia Neotropical.
The same field trip, which extended from 1999 to 2001, uncovered 11 additional species new to science - one opossum, seven bats and three other rodents.
"Like other tropical mountain ranges, such as the Himalayas, the Andes support a fantastic variety of habitats. These in turn support some of the richest faunas on the planet," said research team leader Bruce Patterson.
"The new species is not only a handsome novelty. Preliminary DNA analyses suggest that its nearest relatives, all restricted to the lowlands, may have arisen from Andean ancestors," Dr Patterson said.
"The newly discovered species casts a striking new light on the evolution of an entire group of arboreal rodents," he said.
Little is known about the species except that it lives in the cloud forests at an altitude of 1900 metres and probably feeds on seeds, nuts, berries and small insects.
- REUTERS, INDEPENDENT
