Caverns Give Up Huge Fossil Haul

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Caverns give up huge fossil haul

The Australian landscape was once dominated by great beasts


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An astonishing collection of fossil animals from southern Australia is reported by scientists.
The creatures were found in limestone caves under Nullarbor Plain and date from about 400,000-800,000 years ago.

The palaeontological "treasure trove" includes 23 kangaroo species, eight of which are entirely new to science.

Researchers tell Nature magazine that the caves also yielded a complete specimen of Thylacoleo carnifex, an extinct marsupial lion.

'Took my breath away'

It appears the unsuspecting creatures fell to their deaths through pipes in the dusty plain surface that periodically opened and closed over millennia.

Most of the animals were killed instantly but others initially survived the 20m drop only to crawl off into rock piles to die from their injuries or from thirst and starvation.



The preservation of many of the specimens was remarkable, said the Nature paper's lead author, Dr Gavin Prideaux.

"To drop down into these caves and see the Thylacoleo lying there just as it had died really took my breath away," the Western Australian Museum researcher told the BBC's Science In Action Programme.

"Sitting in the darkness next to this skeleton, you really got the sense of the animal collapsing in a heap and taking its last breath. It was quite poignant.

"Everywhere we looked around the boulder piles, we found more and more skeletons of a very wide array of creatures."

In total, 69 vertebrate species have been identified in three chambers the scientists now call the Thylacoleo Caves.

These include mammals, birds and reptiles. The kangaroos range from rat-sized animals to 3m (nearly 10ft) giants.


Dr Prideaux's team continues to investigate the Nullarbor fossils


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The team even found an unusual wallaby with large brow ridges.

"When we first glanced at the animal, we thought they were horns; but on closer inspection we realised they must have performed some sort of protective function," Dr Prideaux explained.

"The beast must have been sticking its head into spiny bushes and browsing on leaves."

The 'Ancient Dry'

The scientists' investigations indicate the ancient Nullarbor environment was very similar to that of today - an arid landscape that received little more than 200mm of rainfall a year.

What has changed significantly is the vegetation. Whereas the Thylacoleo Caves' animals would have seen trees on the plain, the modern landscape is covered in a fire-resistant chenopod shrub.

This observation goes to the heart of a key debate in Australian palaeontology, the team believes.


The caves and their contents were first discovered in 2002


More details

The continent was once home to a remarkable and distinctive collection of giant beasts.

These megafauna, as researchers like to call them, included an immense wombat-like animal (Diprotodon optatum) and a 400kg lizard (Megalania prisca).

But all - including the marsupial lion - had disappeared by the end of the Pleistocene Epoch (11,500 years ago).

Some scientists think the significant driver behind these extinctions was climate change - large shifts in temperature and precipitation.

But Dr Prideaux and colleagues argue the Thylacoleo Caves' animals give the lie to this explanation because they were already living in an extremely testing environment.

"Because these animals were so well adapted to dry conditions, to say that climate knocked them out just isn't adequate. These animals survived the very worst nature could throw at them, and they came through it," co-author Professor Bert Roberts told BBC News.

"If you look at the last four or five glacial cycles, where the ice ages come and go, the animals certainly suffered but they didn't go extinct - they suffered but survived," the University of Wollongong scientist said.

This assessment would be consistent with the other favoured extinction theory - extermination by humans, either directly by hunting or indirectly by changing the landscape through burning.



As the name suggests, there are precious few trees on the Nullarbor Plain

http://news.bbc.co.uk/2/hi/science/nature/6296029.stm

 

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Humans Caused Australia's Ice Age Extinctions, Tooth Study Says
Sean Markey
for National Geographic News

January 24, 2007
An underground trove of fossil skeletons found in Australia suggests humans, not climate change, drove the continent's large land animals to extinction 40,000 to 50,000 years ago.

The conclusion is based on the first scientific analysis of a rare cache of fossils exhumed from three caves in the arid Nullarbor Plain of southern Australia.



First discovered in 2002, the three- to four-million-year-old caverns have yielded fossils of 70 animal species dating from 800,000 to 400,000 years ago.

The menagerie includes 10 intact skeletons of Thylacoleo (lionlike marsupials), a nearly hippo-size giant wombat, and 23 kangaroo species—8 of them new to science.

Gavin Prideaux, a paleontologist at the Western Australian Museum who led the study, said the fossils are remarkable for their diversity and near-perfect condition.

The ancient bones also open an unprecedented window to the environment and climate of that part of Australia during the mid-Pleistocene (800,000 to 200,000 years ago), Prideaux said.

The findings reveal important clues to what eventually drove the plain's large Ice Age animals extinct.

Teeth Tell the Tale

The Nullarbor region receives just 8 to 10 inches (20 to 25 centimeters) of rain a year.

"It's incredibly dry and bleak," said study co-author Richard Roberts, a geologist at the University of Wollongong. "Things don't get much worse than that for an animal in search of free water."

But animals do survive there, including hundreds of bird species as well as wombats and kangaroos.

The rich diversity of species found in the ancient caves shows that life was similarly thriving in the region during the Ice Age.

Two new species of tree kangaroos, for example, indicate that 300,000 years ago Nullarbor Plain wasn't as treeless as its name implies.

Researchers also found lizards that favor dry conditions and a high ratio of grazing species.



But the most telling clues, the team says, come from an analysis of tooth enamel from 13 species of ancient kangaroo and a giant wombat.

Isotopes found in tooth enamel can signal the abundance of standing water and certain types of grasses.

Researchers compared their results with a database of similar studies of enamel from modern-day kangaroos and wombats.

The results, reported in tomorrow's issue of the journal Nature, show that Nullarbor was as parched back then as it is now.

Tipping Point

According to John Long, a paleontologist at Museum Victoria and study co-author, the findings "have virtually nailed that climate change wasn't a major factor" in the animals' extinction.

"We were able to establish that this entire assemblage of [Ice Age] megafauna animals was adapted to aridity."

Australia's Ice Age creatures probably employed adaptations like those found in modern kangaroos, the paleontologist said.

Living 'roos can survive on the water from plants alone and time their reproductive cycles to coincide with rainy periods.

Roberts, the Wollongong geologist, said Australia's ancient animals "already were very well adapted to some pretty awful climates, and they didn't get any worse than they did on the Nullarbor Plain."

He notes that a recent study in the journal Geology by many of the same team members suggests that Australia's megafauna were very resilient to climate change.

The scientists therefore believe that hunting pressures and wildfires linked to ancient humans may have finally tipped the balance against Australia's large animals.

As climate shifted, the animals suffered, Roberts said. "But they always bounced back—except about 40,000 to 50,000 years ago, [after which] they never bounced back.

"And the only difference is that people were around on the scene at that stage."

http://news.nationalgeographic.com/news ... ssils.html