Caverns give up huge fossil haul

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

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.

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.

All shapes

"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.

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 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.


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