It's the first morning in the field and Creaser, a geologist, kneels in the red dirt of Queensland's Gulf country, 200 km northwest of Mount Isa. His right hand clutches a crack hammer, which is poised over a piece of rock the size of two bricks. What's inside the rock will make Creaser's day and remind the rest of the party that, for all the wonders this place has yielded, it has much more to give. "Work at Riversleigh," says team leader Mike Archer, "will go on forever."
Creaser is entitled to feel hopeful as he takes aim. As fossil deposits go, Riversleigh is like a golf course where you can't help but shoot sub-par. Bones abound: even the untrained eye can spot them protruding from the gray limestone outcrops. In an area of 40 sq. km, Archer's teams have found and named hundreds of sites since 1976, when he and palaeontologist Henk Godthelp decided to check out reports that Riversleigh - then a cattle station, now part of Lawn Hill National Park - might contain valuable fossils. And it did - in the same way that the Louvre could be said to house some nice paintings. Riversleigh has since provided an annual bounty of exquisitely preserved bones and teeth, the remains of creatures - fish, frogs, crocodiles, turtles, snakes, birds, marsupials, bats - that lived anywhere up to 25 million years ago, when Riversleigh was a thriving rainforest in a cooler, wetter (and more southern) Australia. In so doing, the site has filled in what were once gaping holes in our understanding of the origins of modern Australian fauna. "Only in one or two places on the surface of our planet, in the course of the last three thousand million years, have conditions been just right to preserve anything like a representative sample of the species living at any particular time," naturalist Sir David Attenborough wrote in 1991. "Those places are the rare treasure houses of palaeontology. Riversleigh is one of them."
But lately Archer, among others, has begun to view Riversleigh as more than just a portal into the ancient past. It is also, he believes, a harbinger. In stunning detail, Riversleigh chronicles a collapse in Australia's mammal diversity in the past 25 million years. Archer warns that if humans don't stop abusing the earth and "incarcerating our precious biotas in reserves that are demonstrably too small to sustain them," we could jeopardize our survival as a species. Alarmist? Keep in mind, he suggests, that the average mammalian species hangs around for 5 million years; Homo sapiens has been around for some 300,000 years. "We haven't been tested yet."
A single strike breaks the rock in two, revealing a mass of bone in each piece. Creaser gazes at what he recognizes to be the jaws of a largish animal, one that perished some 24 million years ago. But what kind of animal? The others gather around, including Archer, who's one of Australia's best at classifying - all but instantly - what would look to most people like generic bone. "The finest specimen of a marsupial lion jaw that's ever been found," he declares. It seems to have belonged, he explains later, to a previously unknown, intermediate species of this most ferocious marsupial - a link between the cat-sized Priscileo and the leopard-sized Wakaleo - whose lineage coexisted with Aborigines before dying out 35,000 years ago. "Nearly 30 years of digging," says Lizard Cannell, the team's explosives expert, "and we're still finding firsts. All the time."
Compared to years past, it's a small group that assembles in Mount Isa for this June-July dig. Volunteers have previously swelled the team to a force of more than 50. This time it's just nine workers - six men, three women (plus some family) - who pile into several sturdy vehicles for the four-hour trip across rough road. Teams used to camp by the banks of the Gregory River, and regulars speak wistfully of those times. Alas, local authorities banned the practice, pushing the scientists a little further north to the more comfortable, if less invigorating, facilities of Adels Grove camping ground.