Did humans wipe out Australia's big beasts?

This week– play a smaller role in determining species diversity in Australia than has been thought, he says. Australian megafauna died out roughly 40,000 years ago, and Prideaux says the discovery that they survived in an arid environment undermines one of two popular theories for what killed them off – namely, that ice-age aridity was responsible. That leaves the second theory, which suggests that the giant kangaroos and wombats were wiped out by the actions of humans, either through habitat destruction or hunting, says Prideaux. That conclusion is supported by other discoveries by teams led by Prideaux in the Naracoorte caves in south-eastern Australia. Fossils here showed that many species of megafauna survived the recent ice ages – except the last one, which occurred after humans had arrived (Geology, vol 35, p 33). “We’re never going to find a diprotodon [one of the largest extinct marsupials] with a spear in it, but this is as close as you can get to nailing the argument,” says team –At least we know what killed this one– member John Long of Museum Victoria in Melbourne. what they had been eating – Not everyone is convinced, and hence the kind of climate they however. “You can say that a species experienced – the team analysed was arid-adapted 200,000 years ago, the oxygen and carbon content of but you can’t then extrapolate to the tooth enamel from fossils of 40,000 years ago and say ‘So humans 13 kangaroo species, including must have done it,’” says Judith Field several giants, and one species of of the University of Sydney. “It’s far giant wombat. The composition was too simplistic.” similar to that of the tooth enamel of Field argues that archaeological kangaroos and wombats living today finds from Cuddie Springs in southon the parts of the Nullarbor that are eastern Australia, the only place extremely dry, indicating that the fossil animals had also lived in an “We’re never going to find a arid climate (Nature, vol 445, p 422). diprotodon with a spear in it, However, the wide variety of but this is as close as you can herbivore species represented by get to nailing the argument” the bones – 23 species of kangaroo alone, some of which could climb trees – suggests that the Nullarbor where human and megafauna must once have had much more remains have been found in the varied vegetation than the few same place, do not show that the species of shrub it sports today. animals were hunted. “It’s astonishing. I never imagined She prefers the idea that different tree kangaroos on the Nullarbor species were driven to extinction Plain. Australia’s arid zone was clearly at different times and places. once capable of supporting a much Combinations of events, including wider variety of browsing animals,” the stress of the later, more severe ice says Tim Flannery of Macquarie ages, could have been responsible, University in Sydney. Climate may she says. Rachel Nowak ●

CLAY BRYCE/ WESTERN AUSTRALIAN MUSEUM

Did humans wipe out Australia’s big beasts?

TO ANIMALS unfortunate enough to fall in, it was a death trap. To palaeontologists, it was a sensational discovery. Now the first detailed analysis of a spectacular cache of fossilised prehistoric “marsupial lions”, giant wombats and kangaroos, owls and parrots discovered in a cave in Australia suggests that humans killed off the continent’s megafauna. The cache, found in the Nullarbor Plain in south-central Australia, contains fossils of 69 species of mammal, bird and reptile, and includes many complete skeletons, including the first of a marsupial lion (see Photo). There are also eight species of kangaroo that had never been recorded before. The site was discovered by cavers in 2002, but its size and depth – 20 to 70 metres below the desert – means that it has taken a team led by Gavin Prideaux of the Western Australian Museum in Perth four years to collect and analyse the fossils. The team found that the animals fell into the caves between 800,000 and 200,000 years ago. To work out 10 | NewScientist | 27 January 2007

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THIS WEEK 50 YEARS AGO Supersonic flight to go ahead THERE seems little doubt that a supersonic airliner will be built in Britain during the next 10 years. On the initiative of the Ministry of Supply the project has been under discussion by seven firms in the aircraft industry. Associated with them are two airline operating companies. All the schools of design are being discussed – the plain swept wing, the delta and the curly crescent – and only an advocate for the straight, thin, equal-camber wing is missing, although this is still being studied by researchers at Farnborough. There is even fanciful talk of an M-shaped wing, which has the advantage of combining the reduced drag of a swept wing with a lighter load, but building such a wing with strength factors for all flight conditions, including the torsion experienced at supersonic speeds, would require exhaustive research. One other key factor needs to be discussed, though, and that is the economics. The price a commercial operator is prepared to pay for speed is not expressed in terms of military advantage but in cost per ton-mile and utilisation. Drag, and thus fuel consumption, goes up furiously from about Mach 0.85 (610 miles per hour) to Mach 1.05 (750 mph) and the aircraft costs much more to operate. This increment in speed is not worth the cost to a commercial operator, but if speed increases further, the drag coefficient flattens out, and running at about 1000 mph can provide a costeffective return trip across the Atlantic in 24 hours, providing the aircraft is allowed reasonable take-off and landing speeds. The operation of such a commercial venture will, whatever the design, involve considerable cost, the real value of which may ultimately be recouped in the employment of the considerable numbers of people required to design, build and maintain the airliner. From The New Scientist, 31 January 1957

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