[Aqualist] Quaternary in the news

[Tim Barrows]

http://www.abc.net.au/science/articles/2009/06/23/2606054.htm


Giant kangaroo extinction theory disputed

Tuesday, 23 June 2009 
<http://www.abc.net.au/profiles/content/s2193248.htm?site=science>Anna Salleh
ABC

Claims that the largest ever kangaroo was hunted to extinction in 
Australia 45,000 years ago are "unsubstantiated", says one archaeologist.

But the conclusions have been defended in the latest round of 
argument over megafauna extinction, triggered by a new paper in this 
week's <http://www.pnas.org/>Proceedings of the National Academy of 
Sciences on the giant Pleistocene kangaroo, Procoptodon goliah.

Palaeontologist Dr Gavin Prideaux of 
<http://www.flinders.edu.au/>Flinders University in Adelaide and 
colleagues found carbon isotopes and microscopic scratches in the 
teeth the 230-kilogram kangaroo, which suggests it ate tough 
drough-tolerant plants.

Given the kangaroo's bones are distributed in dry regions where the 
hardy, drought-tolerant saltbush grows they conclude this was its main food.

An analysis of oxygen isotopes in the kangaraoo's teeth back up the 
conclusion, suggesting it had to drink a lot from water holes to 
counteract the salt from plants it ate.

Prideaux says this and other evidence suggests the kangaroo was 
adapted to dry conditions, and says this undermines the idea that 
climate change was the reason the animal went extinct.

He says saltbush does not burn well, which undermines another theory, 
that human burning of the landscape was the cause of extinction.

Prideaux says this all points to hunting as the only viable theory to 
explain the animal's extinction.


"Unsubstantiated"

But archaeologist Dr Judith Field of the 
<http://www.usyd.edu.au/>University of Sydney rejects this conclusion 
as "completely unsubstantiated" and a "giant leap of faith".

She says the research provides "terrific" information on the diet and 
distribution of the P. goliah.

But just because the kangaroo was adapted to aridity doesn't mean it 
was hunted to extinction and was not vulnerable to extreme aridity, says Field.

Her main concern is that there is no direct evidence showing the 
kangaroo was hunted by humans.

"If you're going to make any case about humans and these megafauna 
then you've got to have them in the same place in the same time," she says.

"You've got to find archaeological sites that have megafauna in them 
with evidence of butchering. And we just don't have these."

Field has previously reported evidence that humans and megafauna 
coexisted happily for 15,000 years at Cuddie Springs, but this 
evidence is disputed.

She says around 65% of megafauna were gone by the ice age 130,000 
years ago - long before humans arrived in Australia.

This suggests the harsh climate at the time may well have been a 
factor in the extinction of megafauna.


The 'odds favour' hunting

But Prideaux says both humans and giant kangaroos were generally 
occupying the same dry parts of Australia 50-45,000 years ago and it 
is unlikely they could have avoided one another.

"It's not hard to put two and two together and say it's a possibility 
that as those animals came down to waterholes where humans were 
hanging around, they may have picked them off," he says.

"Let's face it, saltbush-fed sheep taste really nice, it's quite 
possible saltbush-fed kangaroo taste really nice as well."

Prideaux says it would not take the hunting of many kangaroos to put 
a dent in their population, since such large animals reproduce slowly.

He says this would make it highly unlikely scientists would find 
bones from butchering in the record.

Prideaux rejects Field's estimate of what proportion of the megafauna 
had become extinct prior to human arrival and calls for more evidence.

He says knowing what happened in the 100,000 years before humans 
arrived is crucial to understanding more about the cause of megafauna 
extinction.

But he says we just don't have enough data to know what happened at this stage.

Field agrees there is a dearth of data.

"We are dealing with an incredibly thin data set here," she says.

"When you are dealing such thin data sets you can invoke just about 
any explanation you like without any fear of it being tested."