by Tim Flannery
The creature was the size of a Tasmanian devil (or perhaps a little larger) and was the largest kangaroo then known from Riversleigh. To my dismay the most complete jaw recovered had lost its premolar to blasting powder. Thankfully a natural mould was preserved in the surrounding rock and I made a cast of the missing tooth with resin before dissolving the stone in acid. Michael Archer and I named the new species Ekaltadeta ima meaning ‘powerful tooth’ and ‘condemned to die’ in an Aboriginal language of the Northern Territory, a name inspired by the missing premolar, which was clearly of massive proportions. Ekaltadeta is the earliest known member of the Propleopus lineage, and its description was a start to the studies I had so long hoped to complete, but until I could examine all of the Propleopus material held in the world’s museum collections I would not be able to fathom the significance of those huge, buzz-saw-shaped teeth.
Mike Archer continued to explore the Riversleigh region in 1981 while I left with Tom Rich for the Northern Territory to investigate another fossil locality. Bullock Creek is on a property several hours’ drive south of Katherine, and when we arrived I puzzled over the long, sinuous flat-topped hill that wound its way over the landscape. Only on close examination did I realise it was all that remained of a mighty river channel whose water carried so much carbonate that limestone had formed in its bed. Over the millions of years since the river had dried up, erosion had removed much of the softer, surrounding rock, leaving the limestone-filled channel standing at least ten metres above the plain.
In the bends of the ancient river system the bones of thousands of huge extinct animals could be seen bristling from the rock. They had been deposited at ‘point bars’, which are well known to those who swim in or camp by rivers because sandy spits often form in such places. This is where the current slows as the river bends, allowing things carried in the flow to drop to the bottom. The limestone enclosing the bones was white, while the bones themselves were as black as ebony, making the Bullock Creek fossils some of the most spectacular I had ever seen. Slightly acidic rain had dissolved the stone faster than the fossils, leaving the bones standing out like a bizarre Egyptian bas relief. As evidenced by their fossilised remains, huge crocodiles and giant goannas must have flourished in the region; but the most common creature by far in the deposits was a species of Neohelos, a relative of the diprotodon and about as large as a calf. Around 10 to 20 million years ago entire herds of these wombat-like creatures must have drowned in ancient floods, for their skeletons formed great mats in the limestone. The remains of kangaroos were, I discovered to my disappointment, much rarer. Only three rather uninformative fossils were found, all balbarines of a species about the size of a rock wallaby.
There is one final fossil locality that adds to our understanding of the changing situation in central Australia, and to the evolution of kangaroos. It is on Alcoota station near Alice Springs, and although we cannot date the two fossil-bearing layers found there, they seem to hail from a time when major deposition at Riversleigh had ceased. Peter Murray, the scientist who has excavated the site, estimates that the two layers may be around 8 and 6 million years old. The fossils preserved therein reveal that by this time rainforest had given way to more open environments—perhaps shrubfields, woodlands or savanna—that supported herds of ponderous diprotodontids and relatives, of which there are four kinds, the largest the size of a cow. These creatures shared the landscape with several species of dromornithids, including Bullockornis, the largest bird that ever lived. Pat Rich, who described this monster, has a cardboard cutout of its leg mounted on the wall of her office at Monash University. The top of its femur stands well above head-height.
It is also in these deposits, laid down towards the end of the Miocene, that we find evidence of the first kangaroos to reach anything larger than wallaby-size. Hadronomas, one of the earliest members of the short-faced kangaroo subfamily Sthenurinae, was as big as a grey kangaroo. It shared its habitat with a much smaller (fox-sized) species known as Dorcopsoides, which is the earliest of the macropodines, and it is with this creature that we see the piccaninny dawn of our modern age.
13
The Age of Kangaroos
Following the fleeting appearance of Dorcopsoides on the central Australian stage around eight million years ago, a frustrating dark age draws a curtain over our window on the past. When the curtain lifts, around 4.5 million years ago, a very different set of animals has populated Australia’s stage. From the dainty striped wallaby to the great grey kangaroo, the macropodine genera as we know them today are all arrayed before the palaeontologist, and forever after kangaroos dominate Australia. From browsers to grazers and fungivores to carnivores, for over four million years their increasing dominance was such that by the ice age (when the megafauna roamed the land, between about 2.4 million and 50,000 years ago) Australia was home to over eighty species of kangaroo.
We still live in the age of the kangaroo. But what of its initial flowering? Aided by its truffle-loving rat-kangaroos, southeast Australia is, from its mallee to its snow gums, a land of eucalypts. Five million years ago, however, rainforests still covered enough of southern Australia to support tree-kangaroos, and most of what we know of the animals that lived in those forests comes from a fossil locality situated in the grassy woodlands of Victoria’s Western District. The fossils owe their preservation to a catastrophe that occurred 4.46 million years ago when a lava flow overwhelmed an ancient rainforest, burning it off at the stumps and instantly freezing all biological activity. Very few bones are found at the site. Instead what you find are the exquisitely preserved enamel caps of teeth—the hardest part of the skeleton—all stained navy blue and as sharp as the day they cut their last food.
When I first saw the Hamilton site with Tom Rich in 1974 I was unimpressed. It lies at the bottom of a sheep paddock beside a grossly polluted creek known as the Grange Burn, whose banks have collapsed and eroded through thousands of cloven hooves. Yet this was once a pretty place, for upstream a waterfall tumbles into a peaceful amphitheatre, while a few reeds and white-flowering Bursaria cling to the most inaccessible niches, reminders of a more diverse vegetation. Tom recounted that the site had been discovered some thirty years earlier by the Reverend Edmund Gill, a parson of scientific persuasion and Tom’s predecessor at the museum, who in his wanderings had plucked a solitary molar from the fossil soil below the basalt. The tooth, which had the appearance of a shrivelled pea, once graced the mouth of a Propleopus. The find had inspired a group of Americans to excavate, and they recovered the isolated teeth of many other animals, but nothing more of Propleopus.
Tom had brought us here because the Hamilton site was, he said, the ‘Rosetta stone of Australian palaeontology’. Not only had the basalt preserved the site, but a technique known as potassium-argon dating (the ratios of these two elements give an estimate of when the basalt congealed) allows geologists to determine its precise time of formation—in this case 4.46 million years ago. There are very few precisely dated sites in Australia, and comparisons with the Hamilton site have permitted the ages of many other fossils to be estimated. Our job was to unearth more fossils so that those estimates could be refined. For my part, I was keen to learn more about Propleopus. The whole idea of such a creature seemed preposterous to me and, as I was to learn, in many ways the giant rat-kangaroo is one of the most bizarre creatures that ever lived. Yet so elusive was evidence of it that I had taken to calling it the ‘probably hopeless’ because I despaired of discovering anything more about it.
For sixteen days we moved innumerable basalt blocks weighing several tonnes apiece and sieved many cubic metres of fossil soil without finding a single fossil tooth. Tom was doing his best to hold the field crew together, buying chocolate and steak for the teenage volunteers out of his own pocket. Nevertheless, conspiratorial whispers about whether we were digging at the right spot were frequently to be heard, and there was even talk of desertion. But then, late on the seventeenth day, after most of the field crew had packed up
and gone home, one of the volunteers caught the glint of ancient blue tooth enamel in the bottom of his sieve. It was not a tooth of the longed-for Propleopus but that of a smaller, more ordinary kind of kangaroo. Still, I considered that we had struck paydirt, and from then on was ready to toil year after year beside the polluted waters of the Grange Burn.
While working at Hamilton we stayed at the shearers’ quarters on a nearby pastoral property in a rolling landscape of grassland and stately red-gums. Tom had secured this luxury in an unusual manner. Several years earlier he had been told of a grazier who was the proud owner of the skull of an Irish elk. The fossil was in need of expert attention, for its teeth were coming loose. The Irish elk was a denizen of the European ice age and a giant of the deer world, its antlers measuring nearly three metres across. Even today a splendid set of antlers is occasionally dragged from an Irish bog, though good skulls are rare and among the prized possessions of many museums. Tom, sceptical that one might reside near Hamilton, nevertheless decided to pay a visit and sure enough, there in the hall of the nineteenth-century farmhouse hung one of the most splendid Irish elk skulls he had ever seen—much grander than the one owned by the Museum of Victoria. The grazier’s ancestors, it transpired, were Irish aristocrats and had shipped the heirloom across in the 1840s. Two years after administering some dental care to the fossil, Tom raised the issue of accommodation, and use of the shearers’ quarters for his field crew was readily proffered.
At first the arrangement seemed ideal, for the century-old building was comfortable and roomy, comprising a large kitchen and numerous bunk beds. But we soon learned that you had to be careful when wandering far from the door, for the place was located in the bull paddock. Everything was fine at first, with the bulls remaining in a distant corner of their domain. Then a herd of heifers was moved into an adjacent paddock. To our consternation these shameless hussies began to idle their time away beside the fence in the vicinity of the shearers’ quarters, flaunting their posteriors and generally teasing the bulls mercilessly. One bull, driven to distraction by this display of bovine pulchritude, decided to leap the fence but, lacking the agility of a kangaroo, his hind-leg became entangled in the wire and was sprained. Once among the females the poor fellow could do nothing, for every time he tried to mount a willing heifer his gammy leg would give way and frustrated bellowing would fill the air. When he was returned to his own paddock with his mood considerably soured, we became even more cautious when wandering outside for firewood and other essentials.
One hot summer night we discovered that bulls were not the only hazard in the paddock. A sinister reptilian head emerged from a knothole in the wooden floor, quickly followed by a metre of tiger snake. The creature had not noticed that the room was occupied until enough of its body had passed through the knothole to make retreat impossible, so instead it decided to advance and bluff its way out. In an instant the room was awash with panicking people, which in turn panicked the snake further. Unable to locate the hole it arose from, it shot about the room full of fury and venom, striking out in all directions as it searched for an alternative escape route. Half a dozen of us shared the tabletop while one of the more nimble volunteers leapt onto the mantelpiece where he did a marvellous job of balancing for several minutes. Someone finally plucked up the courage to descend to the floor and open the door, allowing the snake to flee into the night.
One year, wanting to scout the region for other fossil localities, I arrived a few days in advance of the rest of the crew. The shearers were still in residence, and that is when I met Tom the shearers’ cook, a pint-sized fellow well known in the district for his eccentric ways. When the owner’s son introduced me as ‘Tim Flannery, the fossil hunter’, both he and I were astonished at the warmth of Tom’s welcome.
‘Oh mate, I’ve been waitin fer ages fer yer to turn up!’ Tom exclaimed as if I were a long-lost brother. ‘What would yer like to eat—sausage rolls?’
Soon there was a pile of them on the table—and a bottle of tomato sauce—and for a couple of days Tom and I got on famously. I took all of this to be a symptom of his eccentricity, but then—inexplicably—his enthusiasm for me began to cool, until by the end of the week he seemed hardly able to bear the sight of me. Perplexed, I asked one of the shearers what was going on. Tom, it seems, was a little hard of hearing and had mistaken my being a fossil hunter for a possum hunter. He was thus understandably irate that numbers of the furry creatures—the only marsupials in the area—had not diminished at all during my stay, and that I had kept to my cot at night when I should have been out hunting.
Tom had a special reason for hating possums. In the absence of other nesting places in that denuded landscape, they had sought refuge in the roof cavity of our quarters, where the ghastly growling of the males (which sounds like rasping, heavy breathing) was keeping everyone awake at night. This had not helped the mood in the shearing shed, and when one of Tom’s stews had been impugned with suspicion of pollution from the possum-piss-stained ceiling, the cook’s hatred had turned virulent. Thinking that my arrival was a last-minute bid by the cocky to avert bloodshed, he had greeted me as a saviour. But as my laziness became evident, Tom’s disappointment knew no bounds. The shearers, it transpired, had caught on to the joke and were making things worse by spreading a rumour (alas, all too true) that one evening while driving back from the Branxholme hotel I had even swerved to avoid running over a possum! The Branxholme, incidentally, was a great place to drink, for the clock had no glass on its face and when the local policeman was at the bar the time always seemed to show five minutes to closing. Tom and I were never reconciled, but with the shed ‘done’ the shearers and their cook moved on, and Tom Rich’s volunteers began arriving for another summer’s work.
14
Advancing with Feet or Stomach?
Each field season on the Grange Burn revealed a little more of the ancient rainforests that once thrived in Victoria. We learned that the tree-stumps burned off by the basalt flow were celery-top pine, which still grows in Tasmania, yet the fossil teeth we uncovered were like nothing from our southernmost state. Upon breaking open a clod of blueish-grey soil one afternoon, I discovered the distinctive teeth of a type of wallaby known only from the mountains of New Guinea, over 3000 kilometres away to the north. And a few days after that, the tooth of a tree-kangaroo emerged from one of the sieves we used to wash the ancient soil.
Making sense of such finds took some time, but my understanding of the area grew after wandering a few hundred metres downstream to a dome of pink granite-like rock that jutted out from the creek bank. On its upstream side fossil soil lapped its base, while against its downstream face lay sediments formed in an ancient Bass Strait. Here, some eighty kilometres from the modern coast, was the ancient shoreline, complete with oysters, the bones of whales and even the teeth of great white sharks that once swam in its waters. Four and a half million years ago the pink dome of rock must have stood as a bulwark against the force of the Southern Ocean, and in its lee grew our ancient rainforest, perhaps watered by the ancestor of the Grange Burn itself.
It was now 1980, and after four seasons of digging we had turned up only eight isolated teeth belonging to Propleopus which, to add to my frustration, were sent to an expert for study. To me, however, fell the immense pleasure of describing the other kangaroos from the site. There were now hundreds of teeth representing over a dozen species. A close relative of Queensland’s musky rat-kangaroo shared Hamilton’s ancient forests with a larger rat-kangaroo of the bettong type, but the most common creature was very similar to the Tasmanian pademelon (Thy-logale billardierii), which vanished from Victoria a century ago. Hundreds of its teeth had been unearthed, indicating that it was then as dominant in Victoria as its descendant is today in Tasmania.
The genus name for pademelons, Thylogale, means ‘pouched weasel’, which the creatures most emphatically do not resemble. They are instead rather nondescript wallabies, all six species of which inhabit the margins of rainfor
ests and dense scrub from Tasmania to New Guinea. They may well be the ancestral type from which the great kangaroos, striped wallabies, rock-wallabies and tree-kangaroos have sprung, so in some ways they are living fossils. Studying their teeth, I was amazed to see how little the lineage had changed in 4.46 million years. So successful is the Tasmanian pademelon that permits are given to farmers to cull them. While this may seem odd, the creation of pasture by Europeans has benefited it greatly, justifying a sustainable harvest. And besides, its flesh is so far superior to that of the kangaroo that a more basic argument may persuade people to sample it. Were it more readily available, pademelon would be one of Australia’s premium meats.
Almost as common at the Hamilton site were the teeth of a forest wallaby (genus Dorcopsulus) of a sort today restricted to the mountains of New Guinea. The remains of these hare-sized creatures have not been found at any intermediate localities, so their presence in southern Australia is an anomaly. Also found were the teeth of several larger, long-extinct wallabies, but none of the larger living kangaroos, perhaps indicating that there was no grassland nearby.
The Hamilton fauna was dominated by species of the most advanced kangaroo subfamily, the Macropodinae. This is surprising, for in older deposits (from the Miocene period, 5 to 24 million years ago) the more ancient balbarids and bulungamayines predominate. Their absence from Hamilton indicates that by 4.46 million years ago a continent-wide revolution had occurred in Australia’s kangaroo fauna, with the macropodines sweeping away most of the competition—even in the ancestral rainforests.
