Saturday, January 27, 2007

Why humans are dangerous neighbors

Or, why we no longer have "Giant kangaroos, marsupial lions and wombats the size of a car" (gratefully lifted from Mick Hartley, who is always good at noticing this kind of stuff). Some animals, like cockroaches, love having us around. But for large (non-domesticated) mammals, we have always been bad news. There once used to be lions in ancient Europe and elephants (of the woolly mammoth variety) in North America, too. --Jeff Weintraub

Mick Hartley
January 25, 2007
Giant Roos and Marsupial Lions

The thesis that human encroachment killed off the great megafauna in Australasia and America ties in well with the dates. And in New Zealand, with the extinction of moas and much of the rest of the unique giant bird species happening within historical time, the facts are undeniable. Still, it conflicts with that whole noble savage stuff, where the natives lived in harmony with their environment till the arrival of rapacious Europeans, so there have been plenty of arguments for climate change as the primary cause.

The latest finds in Australia add more weight to the human intervention argument:

Giant kangaroos, marsupial lions and wombats the size of a car survived all that climate change could throw at them but were wiped out by the arrival of mankind, according to a study. Fossil remains of the animals were found in a cave on the Nullarbor Plain, in southern Australia, and scientists have been astonished by the number and variety of creatures preserved.

At least 69 species of mammals, birds and reptiles, a third of them now extinct, have been unearthed at the site after falling and becoming trapped in the deep caves 400,000 to 800,000 years ago.

Among the hundreds of fossils were giant kangaroos that weighed 31½st (200kg) and stood 10ft (3m) high, and the first complete skeletons of Thylacoleo carnifex, the marsupial lion. Eight kangaroo species previously unknown to science were uncovered at the Thylacoleo caves, including two that lived only in woodland, and a giant bird, Leipoa gallinacea.

It had previously been assumed that for the land to support such a range of large animals it would have to have been wet enough to sustain woodland and lush vegetation of a type that is absent from the arid Nullarbor Plain today.

Analysis of the remains, however, has revealed that the climate when the animals died was just as dry as it is now — and yet it supported far more vegetation.

The finding, reported in the journal Nature, means that palaeontologists must rewrite theories on Australia’s environmental history that has hitherto held Ice Age-driven climate change to be the cause of the animals’ extinction. [...]

The research leader, Professor Richard Roberts, of the University of Wollongong, said that the animals had survived repeated climate change yet had disappeared suddenly in the past 50,000 years.

“Suddenly and during quite pleasant climatic conditions when the megafauna should have thrived, they went extinct. Why? The only new ingredient in the mix at that time was humans,” he said.

“Humans very likely played the decisive role in the extinction event through hunting of juveniles, burning of the vegetation cover and changing the plant composition to disadvantage the browsers and grazers.”
January 25, 2007 at 10:23 AM |