by Tim Flannery
‘That’s it there. Can’t you see the flags?’
Sure enough, rising from among the rusting chassis were flags of the kind that mark tees. Marree is a strange place.
In 1980 I had no idea what to expect from Lake Eyre. Despite being known as the rain gauge of Australia (one sixth of the continent drains into it), the Lake Eyre Basin is the driest part of the country. But when the tropical monsoon brings rain to the headwaters of the Cooper Creek in far away Queensland, the stretch of salt crust surges into life, becoming an inland sea whose fresh waters float atop the brine. Then, birds and fish in their millions thrive in the parched interior, which may itself have received no rain at all.
The region has attracted the attention of palaeontologists ever since Scots professor J. W. Gregory led a group of students from the University of Melbourne there in the summer of 1901. University holidays seem perversely scheduled to torment those who are desert
Encasing fossils in plaster for safe transportation is a filthy job. As Tom’s volunteer I crawled under this block to plaster the overhead base. I’m wrapped in hessian to keep the wet plaster, dust and flies off my skin.
or tropics-bent, but Gregory’s team did remarkably well, finding an extensive outcrop of fossil bones on Cooper Creek. But these were recent specimens—none more than a million or so years old, and I was interested in far older fare. (Gregory, incidentally, drowned in the Amazon River, an odd end for a man whose reputation was made in deserts.)
On that trip in 1980 I camped with Tom Rich and his wife Pat, also a palaeontologist. We had come to look for fossils at Lake Palankarinna, but had little luck. To the east of our camp was gibber—the highly polished pavement of desert stone so characteristic of large parts of the Centre. Traversing it one morning we came across a pair of dingoes that had pulled down a female red kangaroo. The blood was still wet on the stones when we stopped to investigate, and the clay between them told of the doe’s dawn struggle for her life. Dingo numbers are so high in this cattle country that reds are a rarity.
Within a few days of our arrival black cloud had built up, sealing in the heat and producing an unpleasant humidity. Upon stepping out of my tent around midnight for relief from the sauna-like atmosphere, I found the ground alive with scorpions, the largest of which were twenty centimetres long. The place was seething with them, with barely room enough to place a foot between the pale, translucent bodies. Perhaps they had emerged to mate or hunt; whatever the cause I have never seen a sight like it before or since. In the small hours a thin scatter of raindrops fell, yet by dawn all signs of the ghostly-pale scorpions and moisture alike had vanished.
In 1982 I had the opportunity to work at the most remote fossil locality in the Simpson Desert. Dating to a more recent geological epoch than those from Lake Pinpa, it outcrops around Lake Ngapakaldi, a small salt lake lying to the northeast of Lake Eyre. Getting there is difficult, involving grinding across the bleached sand of the Cooper Creek, then picking the inter-dune valley that the lake lies in. Choose the wrong valley and you could drive right past without ever seeing the small oval of salt.
The whole region north of the Cooper was as dry as a sunstruck bone during our visit and, with the exception of a teeming mass of rabbits in this pre-calici Australia, appeared lifeless. As we set up camp just south of the lake, rabbits swarmed around us, making me determined to enjoy a roast dinner before we quit the place—a pleasure we arranged that very evening. Dawn comes strangely in this part of the desert. The gradually lightening sky leads first to an awareness of the dry air, and as I lay choking on a dry throat not a single bird gave voice to greet the day. The deathly silence was broken only by a distant pulse—the sound of my own blood pumping.
As we walked the two kilometres that separated us from the lake we saw no spinifex, but instead a miserable sort of cane grass that favoured the dune summit, while a few dead-looking acacia and rattle-pod bushes lay scattered over the inter-dune valley. We continued in silence, carrying tools and water, and I came to appreciate how this most remote of ecosystems had been devastated by European impacts, despite the fact that few Europeans had ever entered it. Too dry to be used for cattle, it had become a paradise for rabbits, and doubtless the foxes and cats that prey upon them. They had eaten the place alive, and all that was left of the native mammals that had thrived fifty years earlier was the odd bone poking out of the dunes. Even the birds and insects had been affected, for the rabbits had stripped much of the vegetation. I have often wondered how this corner of Australia looks now, after calicivirus has purged the place of rabbits, and whether any remnant of those vanished marsupials might have survived to enjoy the arid paradise that, I hope, has sprung up in its wake.
Lake Ngapakaldi’s only distinguishing feature is a scatter of water-worn pebbles on its shore, an unusual thing in this desert of wind-eroded stones, and it marks the bed of a creek that last ran perhaps 20 million years ago. If you dig down deep into the briny, pebbly sand you will hit a layer of thick black clay. Break open a lump, crumble it under your nose, and you will smell something utterly different from the dusty, salty and bitter smell of the desert; rich organic compost from the floor of a central Australian forest which flourished 20 million years ago.
Whole leaves have been held in suspended animation by that remarkable clay, and although they have turned black they remain as flexible as the day they fell from the twig. But when the leaves are again exposed to sunlight an eon of decomposition catches up with them, and in the time it takes to boil a billy they are nothing but dust. Scientists have beaten the heat and dryness by preserving a few fragments in glycerine, which reveals that Lake Ngapakaldi’s ancient billabong was fringed with reeds, behind which grew trees typical of the rainforest edge; among them was a genus that was to achieve dominance—the eucalypt. Their presence is a clear indication that by Ngapakaldi times the rainforests were breaking up and the seeds of a future Australia were springing up at the continental heart.
The fossil bones we had come to find were concentrated in gravels below the clay. Most were small and water-worn, as if they had travelled a great distance in that ancient stream before coming to rest. Sometimes I would spot the distinctive brown colour of bone protruding from a clod of gravel and break it open to reveal the jawbone of an ancient ringtail possum. The work was like time travel and I was entranced, sweating as I swung the mattock. Another clod might reveal the jaw of a bandicoot, or a wallaby-like creature, the likes of which the world has not seen since the Miocene period 20 million years ago, and as I worked on, in my mind I was soon back in that very different central Australia.
We did not see most of the fossils we excavated, for the gravel had to be dried, broken down in water and picked through under a magnifying glass before they would be revealed. So we bagged up the sediment and loaded it into the Land Rover to await a cool night, preferably with a dew to consolidate the sand. Over the days our stockpile beside the Birdsville Track grew and grew, until a truck picked it up and delivered it to the railhead at Marree, and thence to Sydney.
12
Where the Great Roos Came from
In Sydney we sorted the sack’s contents at Michael Archer’s laboratories in the University of New South Wales, and found that the fossils from Lake Ngapakaldi were typical of those from central and northern Australia which date to the Miocene Period, 24 to 5 million years ago. In 1982 little was known of the kangaroos of this period—just a few teeth, jaws and isolated bones—and they presented a great puzzle. While many teeth looked superficially similar to those of later kangaroos, subtleties of their shape—a cleft in the enamel crown here, a wriggle there—intimated that the same tooth shape may have arisen in entirely different ways in these ancient kangaroos as compared with living species. Yet somewhere here lay the origins of the great kangaroo subfamilies—the Macropodinae and Sthenurinae—that would dominate ice-age and modern Australia.
The ancient kangaroos from Lake Ngapakaldi and similar-aged sites could be divided into two type
s, which myself, Michael Archer (then my PhD supervisor) and Mike Plane of the Bureau of Mineral Resources classified into two subfamilies that we called the Bulungamayinae and Balbarinae. The balbarines were generally larger (about the size of hares), and had molars resembling those of the quokka. We decided that the balbarines were the most likely candidates to be the mothers of all kangaroos, the rat-kangaroos alone deriving from the bulungamayines. But we were soon to learn that the evolution of the kangaroo family resembles a great twiggy bush, where similarities can sometimes be misleading.
The discovery of rich fossil deposits at Riversleigh finally dispelled all doubt surrounding this aspect of kangaroo evolution. Michael Archer had a long-standing interest in Queensland, for he had been curator of mammals at the Queensland Museum before coming to Sydney and, in 1981, he invited me to visit some fossil deposits on Riversleigh station in Queensland’s Gulf country.
Our route lay through Mount Isa and during our overnight stay there we witnessed several brawls; but the sense of intimidation they produced was nothing compared with the feelings the countryside elicited as we travelled towards Riversleigh station. The tropical heat and blistered rocks give the impression that, if lost in that country, there would be no surviving even a few hours without water. Then, almost miraculously, we came across a hidden oasis—the limpid, spring-fed Gregory River. Our base camp was established among the deep green trees of this paradise where waterlilies, freshwater crocs and waterbirds formed an ever-changing panorama. But the place we had come to investigate was not in this verdant strip but on a blasted limestone ridge a few kilometres away.
The following morning, on passing the Riversleigh homestead we discovered that ‘Honest John’ Moloney, a travelling vendor to stockmen, had set up shop at the front gate. It was rodeo time and the young jackaroos had gathered around Honest John’s van, for it was important to look the part when atop a wild bull or bucking bronco, and these men were paying large dollops of hard-earned cash for R. M. Williams belts, boots and hats. The whole ritual, from Honest John’s spruiking of his goods from the back of his gaudily painted van, to the shy Aboriginal youths awaiting their turn to buy, was a vivid reminder that we were in cattle country.
We continued on, finally reaching a low limestone cliff to see where fossils had first been found in 1910. Impressive remains still abounded, in one huge boulder the jaws of massive crocodiles jostled for space with the skeleton of a titanic, emu-like bird known as a dromornithid. Yet the limestone was tough and mammal fossils scarce so we set to work at an old bat roost discovered four years earlier. We broke it apart with explosives, then gathered the fragments and carried them back to the University of New South Wales to be dissolved in acetic acid, thereby releasing the bones.
This Riversleigh expedition was a disappointment to me. At that time only a couple of kangaroo jawbones had been found in the deposits, none of which contributed much to our understanding of kangaroo evolution. But what was worse from my youthful perspective was that there was so little to see at the site, for the major fossil deposits were yet to be revealed.
In 1983 Michael Archer returned to Riversleigh—and hit the jackpot. The new sites yielded thousands of kangaroo fossils, including some near-complete skeletons. Dr Bernie Cook, a palaeontologist from Queensland, elegantly analysed this material, demonstrating conclusively that the balbarine kangaroos, whose teeth look so similar to those of some living wallabies, were in fact an evolutionary dead-end. Rather than being the mothers of all kangaroos, they are a primitive lineage that branched off early in the evolution of the group and led nowhere. It was the rat-kangaroo-like bulungamayines that had given rise to both rat-kangaroos and the more successful macropodines that so dominate Australian environments today. I was not really surprised to see our earlier hypothesis overturned, for it was based on very few fossils, though all that was available.
Bernie’s discoveries provided a vital lesson in the nature of the enterprise I had embarked upon. Sooner or later all scientific hypotheses will be proven wrong or insufficient. That is the way science progresses, and scientists are well served by never allowing too much ego to get tied up in their discoveries, for it is inevitable that other researchers will come along to test, modify and often dismiss their ideas.
Dr Ben Kear, who had been my doctoral student, also studied the Riversleigh kangaroos. His research, which has focused on the few partial kangaroo skeletons found, has provided insights into why the bulunga-mayine kangaroos were so successful while the balbarids vanished. A balbarid kangaroo skeleton lacks several specialisations necessary for hopping. Instead it retained a grasping great toe on its hind-foot (like a possum) and a partially prehensile tail. This suggests that balbarids bunny-hopped, and possibly climbed, through the rainforest. The bulungamayines may have been the very first kangaroos to hop, thus translating the potential of their reorganised hind-limb into the most efficient means of getting about ever devised by a land mammal. This alone may have assured their success, but it seems likely that, in the lineage leading to the kangaroos, wallabies and rat-kangaroos, it was accompanied by a second change which involved their digestion.
Today the macropodine kangaroos, the group that dominates the continent, share Australia with the rat-kangaroos—animals such as bettongs and potoroos. At the time of European settlement ten species of rat-kangaroo lived in Australia, and they were sometimes considered pests. Very few Australians see rat-kangaroos in the wild today, for their numbers are much diminished. This is a tragedy for the Australian environment as these seemingly obscure animals play a vital role in maintaining the health of our ecosystems. They do this by spreading a vital partner of many Australian plant species—the mycorrhizal fungi, otherwise known as ‘Marsupial truffles’.
The mycorrhizae are normally invisible thread-like organisms that remain buried underground. They occur in massive volume in Australian soils, and are strongly attracted to the roots of many plants, around which they form a sheath. Australia’s soils are so infertile that many plants cannot support their growth unless they form a partnership with these fungi, which have a special way of concentrating soil nutrients. In the kwongan heathlands of southwestern Australia around 80 per cent of all plants have an association with the fungi. Even the mighty eucalypts depend heavily upon the thirty-micron-thick halo of fungus that surrounds their roots, allowing them to grow faster, be healthier and recover more rapidly from wilting.
For their part the mycorrhizae gain water and sugars from the plants. But they have a problem. Many are host-specific, and getting from one host plant to another is difficult. This is where the rat-kangaroos come in, for they have as exquisite a nose as any truffle-hunting pig, and can smell the ‘marsupial truffles’ produced by the fungi deep underground. These they dig up and consume, in the process spreading the fungi’s spores. Rat-kangaroos have a greatly expanded stomach, dominated by one very large pouch at its front end, which is used like a sack to store the ‘truffles’. For such small, vulnerable creatures, being able to quickly fill their stomach-sacks, then retreat to shelter, is advantageous, for it minimises exposure to predators.
Rat-kangaroos also assist the environment by turning over the leaf litter, thereby hastening its decomposition and enhancing the water-holding capacity of the soil. The boodie or burrowing bettong (Bettongia lesueur), digs far deeper, and in so doing unearths fertile soil from deep underground. Two hundred years ago these grey, blunt-faced, rabbitsized animals could be found over most of the drier parts of the continent. They did not decline immediately upon European colonisation—so abundant were they around some settlements in the mid-nineteenth century that their penchant for excavating in country cemeteries saw them accused of ‘disturbing the rest’ of the pioneers—but by 1940 they had vanished entirely from the Australian mainland and today survive on just a few offshore islands.
Burrowing bettongs are feisty creatures whose growls and grunts, if disturbed, give adequate warning to human and goanna alike to leave them alone or risk a sev
ere biting and scratching. Their pugnacious nature, however, is coupled with a stunning naivety in the face of obvious danger. Scientists first stumbled across this aspect of their personalities when they had to instil fear of dogs into some island-bred bettongs to be released in a mainland national park.
In order to convince all doubters, the researchers produced a film of the experiment, which shows a fearsome bull-mastiff frothing at the mouth and barking as it strains at the end of its chain, while centimetres from its nose a trusting bettong is stretching towards the open maw, wearing a contented, curious expression. It took many weeks to teach the bettongs that dogs could be dangerous, but even that hard-won knowledge was short-lived, for when the bettongs were retested a few months later they again displayed no fear of the chained dog!
The warrens of burrowing bettongs can still be seen in many parts of Australia. Areas with a hard, almost concrete-like surface layer known as calcrete were especially favoured (which may explain their predilection for burrowing under gravestones). In 2000, on Mount Gibson station, several hundred kilometres north of Perth, I saw some burrows in mulga country with very little shrub or herb understorey. But a very different plant community grew where the bettongs had heaped up great piles of earth from under the calcrete. These plants presumably need the extra nutrients offered by the fresh soil, and possibly support a greater diversity of animals than might otherwise exist. You might think that those inveterate burrowers, the rabbits, would make a good replacement for the bettongs, but their proclivity to eat the plants in the vicinity of their burrows means that the benefits of their excavations extend to few creatures but themselves.
The Riversleigh deposits have yielded the skull and jaws of an animal strikingly similar to the living burrowing bettong, suggesting that these creatures have been enhancing Australia’s biodiversity for millions of years. Other kinds of rat-kangaroos, though, are much more prevalent at Riversleigh, foremost of which, I discovered to my delight, was a relative of the Propleopus that had so intrigued me in the Museum of Victoria years before.
