Over the past decade, palaeontologists and hardy volunteers have been painstakingly blasting and drilling into the base of a 90-metre-high cliff in a remote part of the rugged coast of southeastern Australia – the only dinosaur mine in the world. Buried in the cliff, at the site called Dinosaur Cove, are the remains of dinosaurs that once lived close to the South Pole. The finds from this site, along with bones from the North Slope of Alaska, make a fascinating and controversial story.
They challenge the common perception that dinosaurs only thrived in lush, verdant tropical regions. Instead, they suggest that dinosaurs were able to withstand cold, and survive long periods of darkness – even, perhaps, those caused by the dust thrown up by a meteorite impact. Indeed, some dinosaurs in ancient Australia may have evolved a brain and eyes that helped them to see in the gloom. The research also suggests, but does not prove, that some dinosaurs were warm-blooded. And there is evidence that at least two groups of dinosaurs, common in the northern hemisphere, may have evolved in the supercontinent of Gondwana, from which Australia and Antarctica were formed.
Dinosaur Cove is at the foot of the Otway ranges, coastal mountains about 220 kilometres west of Melbourne (see map on next page). This summer, a team of dinosaur hunters, led by palaeontologists from Monash University, in Victoria, and the Museum of Victoria, are making their last expedition to the site before turning their attention to other, less well explored sites in the Strzelecki coastal region, east of Melbourne. They arrived at Dinosaur Cove in mid-January and will work solidly at three sites for 70 days until early April. Their main task is to use explosives to weaken a pillar of rock that has acted as support for two tunnels. They expect this pillar, which has deliberately been left untouched until this last ‘dig’, to contain the richest seam of fossils ever found at Dinosaur Cove, including more of the skeleton of a hypsilophodont, a small herbivore that was prolific in the region.
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Evidence for antipodean dinosaurs was scanty until the late 1970s; there was just a collection of trackways and two partial skeletons from Queensland. Until 1978, the only fossil evidence of dinosaurs along the coast of Victoria was the claw of a meat-eater called Megalosaurus, found late in the last century by the geologist William Ferguson, who was mapping exposures of early Cretaceous rock. The Cretaceous period, which encompasses both Dinosaur Cove and the Strzelecki sites, lasted from about 140 to 65 million years ago and was the last of three geological periods in which dinosaurs are known. They first appeared in the fossil record just over 200 million years ago during the Triassic.
In 1978 Tim Flannery and John Long, then graduate students at Monash University, found 30 dinosaur bones at Eagles Nest in the Strzelecki, where Ferguson had found the dinosaur claw. Then in 1979 and 1980 Flannery and a group of palaeontologists from museums and universities decided to explore the Otways, which contain coastal outcrops similar to those at Eagles Nest. After a frustrating first year, Michael Archer from the University of New South Wales found a fragment of bone. Tom Rich from the Museum of Victoria scribbled a name for the site in his notebook – Dinosaur Cove. With primitive tools, the palaeontologists soon found another dozen fragments.
Rich and his wife, Pat Vickers-Rich (who is now at Monash University) are both naturalised Australians who were born in the US. They have been leading expeditions to Dinosaur Cove for almost a decade. The first expedition, with 65 volunteers, was in 1984. ‘In 16 frantic days we drilled out an area about the size of two telephone booths,’ says Rich. ‘We found 85 bones and bone fragments, including some limb bones and a dinosaur tooth.’ The expeditions have provided the first comprehensive picture of antipodean dinosaurs and more than 5000 specimens have now been found – a paltry amount compared with sites in North America, but an important tally for Australia. Private companies have provided the explosives, mining equipment, diesel fuel and food that have made the annual expeditions possible. Volunteers, many of them from Earthwatch, a practical conservation organisation based in Massachusetts, have a laborious job of extracting the fossils .
The deposits at Dinosaur Cove were laid down between about 100 and 110 million years ago, when Australia and Antarctica were connected by a rift valley that could have been crossed on foot. Today, Antarctica lies about 2900 kilometres south of Dinosaur Cove, and is separated from it by an ocean. The ancient rift valley was a flood plain. During floods, most likely caused by the annual meltwater from the highlands at the sides of the valley and from volcanic peaks, rivers and streams broke their banks and picked up bits and pieces of plants and bones, along with soft sands, mud and volcanic ash.
Over millions of years, the sediments and the debris were gradually buried as deep as 3 kilometres, as the floor of the rift valley sank. The sediments, with their load of bones, were pressed into hard rock. During the past 30 million years the sediments have been uplifted to form the Otway and Strzelecki coastal ranges. In these types of mountains, the chemical processes which convert rock into soil usually destroy fossilised bones before they are exposed by natural erosion. However, because ocean waves erode the rock so quickly, fossils are exposed before the chemical processes of soil formation take effect.
TIME TUNNEL
The ancient channels, according to Rich, acted like filters. That is why only small bones – small enough to be carried along a narrow stream – have been found. ‘In a way, our sample of dinosaurs is biased,’ says Rich, ‘but we do have fossil evidence of larger dinosaurs such as Allosaurus and Megalosaurus.’ Rich and his colleagues tunnel into the alternating layers of sandstone and mudstone, about a metre above the fossil-bearing deposits. They then use jackhammers to reach the layer of fossils, which is no more than 30 centimetres thick, often much less. Most of the fossils are found in chunks of rock that are carefully broken apart in daylight on the shore platform.
In the Cretaceous, Victoria, and hence Dinosaur Cove, was much closer to the South Pole – between 65 degrees and 85 degrees South, although most estimates suggest it lay near the southern extreme of this range. Today, the area is at 38 degrees South. But in the Cretaceous the world was warmer than it is now, and subtropical conditions extended to about 60 degrees South. This summer, Michael Whitelaw of the University of Texas at El Paso will make palaeomagnetic surveys of these areas to determine more accurately the latitude of the Otway and Strzelecki ranges 100 to 125 million years ago. The method involves measuring the record of past magnetic fields that is preserved in ancient rocks. It is possible to work out what the latitude was from the direction and angle of alignment of these fields with the poles.
Once this palaeolatitude is well established, it should be possible to say how long the area was plunged into continuous darkness each year. The only relief from the gloom would have been occasional moonlight and the aurora australis, or southern lights. If Dinosaur Cove was 70 degrees South there would have been six weeks of continuous darkness each year. If the latitude was 85 degrees South the darkness would have lasted four-and-a-half months. The farther south, the harsher the conditions the dinosaurs would have faced.
A method commonly used for determining palaeotemperatures, called oxygen isotope ratios, involves analysing calcium carbonate in rocks. These measurements suggest that the mean annual temperature was somewhere between -5 °C (that of modern day Nome, Alaska) and 6 °C, while palaeobotanists favour a milder 10 °C (similar to modern London) from their studies of fossilised plants. Rich and Vickers-Rich say that in summer the Sun shone for 24 hours. In winter the nights were long and cold with the air temperature well below freezing, and lakes and rivers froze over. Prominent annual growth rings in fossilised trees from the site found by Judy Parrish from the University of Arizona at Tucson and Robert Spicer from the University of Oxford confirm a pronounced variation in seasons.
The landscape was relatively green and lush, given its southerly location, with ferns and Araucarians being the most prominent plants. Other non-flowering plants included ginkgoes, cycads and podocarps. Angiosperms, or flowering plants, were making their first appearance, but were still a rarity. Both evergreens and deciduous trees grew. Bands of charcoal in the rocks indicate that forest fires occurred.
There was ample food for herbivorous dinosaurs, and where there are herbivores, carnivores are not far away. A meat-eating Allosaurus, a species smaller in stature than its cousins in the northern hemisphere, hunted the plant eaters. The Australian Allosaurus was only about 2.5 metres high, the same size as one of the smallest individuals in a sample of 55 Allosaurus fragilis from a site in Utah. Remains of Allosaurus have only been found at one Strzelecki site but it, or something similar to it, is likely to have preyed on animals at Dinosaur Cove too.
The dinosaurs shared their world with a wide variety of other animals including fish, lizard-like reptiles, primitive turtles that were yet to evolve retractable necks, flying reptiles called pterosaurs, birds, amphibians and plesiosaurs. Most plesiosaurs, large aquatic reptiles with long necks, lived in the oceans, but those of ancient southeastern Australia inhabited fresh water. Perhaps they were a marine species that swam up river to hunt or breed, but Dinosaur Cove was well inland 110 million years ago. So far, more than 150 different species of flora and fauna have been identified as well as 12 orders of insects found.
Rich and Vickers-Rich say that the biota lived under circumstances with no modern counterpart – cool, but not freezing temperatures all year round, combined with a prolonged period of darkness. The dinosaurs needed to be adaptable. Finds from China and Canada have led palaeontologists to speculate that herds of large plant-eating dinosaurs migrated southwards from high latitudes in winter, followed by predators such as Allosaurus.
But Rich and Vickers-Rich believe that in ancient Australia, annual migration of the small dinosaurs at least was most unlikely. Instead, they say, these dinosaurs adapted to the prolonged cold and dark. Most of the fauna in polar Australia were small, and would have found an annual migration of more than 1000 kilometres, across or around inland waterways, exceedingly difficult. Some of the animals may have hibernated by burrowing into the soil and allowing their body temperature to drop to freezing or below. But a find made deep underground at Dinosaur Cove in 1987 suggests that one dinosaur at least was active during the winter.
In that year the dinosaur hunters found a skull which contains what they describe as the ‘exquisitely preserved’ cast of the brain of a juvenile hypsilophodontid, a dinosaur about the size of a large chicken. Natural casts of dinosaur brains are uncommon; those of juveniles are even rarer. What was remarkable about the skull was the size of the animal’s optic lobes – the region where the nerve impulses from the brain are processed to form a visual image. ‘In the skulls of hypsilophodontids from nonpolar regions, the optic lobes do not leave an impression on the brain case,’ says Vickers-Rich. ‘This one has two whopping impressions.’ Such a creature would have been able to adapt to darkness.
LIGHT WORK FOR THE EYES
‘It’s a reasonable assumption,’ says Vickers-Rich, ‘that if you have a dinosaur in high latitudes with a huge area of its brain dedicated to processing light, it’s there to be used.’ Also, if the animal was actively foraging for leaves on the forest floor during winter, it would have required a high metabolic rate. It may, therefore, have been warm-blooded. The specimen, one of five new species of hypsilophodontids found at Dinosaur Cove, was named Leaellynasaura, after Leaellyn Rich, the palaeontologists’ daughter and long-time member of the expeditions.
Many of the hypsilophodontid bones found at Dinosaur Cove are from juveniles. This suggests that adults hatched and reared their young in this region, rather than in warmer latitudes. ‘It’s another reason for doubting that they migrated,’ says Vickers-Rich. The long balmy days of summer, when temperatures could have reached 10 °C or more, could also have allowed the dinosaurs to build up fat for insulation and energy for the winter.
Next season, the dinosaur hunters will turn their attention to the rocky coastal outcrops of the Strzelecki ranges. The smattering of fossils already found along the eastern coast suggest that the Strzelecki region will be even more rewarding than Dinosaur Cove. ‘And we won’t have to do any mining, just digging,’ says Rich.
The Strzelecki sites are 110 to 125 million years old, slightly older than the deposits at Dinosaur Cove, laid down about 100 to 110 million years ago. ‘We will be able to trace the evolution of the dinosaurs over that 25-million-year period,’ says Rich. The method of deposition in the Strzelecki region was different from that of Dinosaur Cove, which may explain why different fauna are being found there. Sediments containing fossils were washed down the sides of fault scarps as the floor of the rift valley subsided. Many bones were buried in these ancient alluvial fans that spread out from the base of the escarpments.
Finds made last year from the Otway and Strzelecki sites are as striking as those from Dinosaur Cove. They suggest that two dinosaur groups may have originated in the southern hemisphere, rather than the northern hemisphere where their remains are common. The dinosaurs do not appear in the northern fossil record until well after the age of the Australian deposits. An ulna – a bone of the lower front leg – was found at both sites, and both bones could have come from a small ceratopsian, a horned dinosaur that first appeared in the fossil record in Asia no earlier than 95 million years ago. The Strzelecki specimen, according to Rich, is strikingly similar in size and shape to that of a ceratopsian, Leptoceratops gracilis, found in 65-million-year-old rocks in Alberta, Canada. When Rich showed the specimen to Dale Russell from the National Museum of Canada he exclaimed: ‘We are in violent agreement! It looks like a ceratopsian.’
Other palaeontologists are likely to question the identification, and therefore the possible migration, of these dinosaurs between hemispheres. The Australian specimen appears to be in the wrong place, both geographically and chronologically, for it to be from the ceratopsian group. The ceratopsians evolved extremely rapidly to become one of the dominant groups of the Late Cretaceous in the northern hemisphere. The group includes the massive Triceratops.
The other find, made by a volunteer at Dinosaur Cove, was a vertebra and several leg bones of what appears to be an ornithomimosaur, an ostrich-like dinosaur that was also abundant in the northern hemisphere in the Late Cretaceous. The specimens are primitive when compared with ornithomimid fossils from the Tyrrell Museum of Palaeontology in Alberta, says Rich, but the Australian find complements an earlier one from Tendagaru in East Africa. According to Rich, the finds suggest that ornithomimosaurs evolved in Gondwana. Africa and Australia were part of Gondwana until about 150 million years ago. What is not clear from the fossil record – because of the paucity of material – is what happened to these dinosaurs in the southern hemisphere.
Earlier finds from the Strzelecki are also controversial. They suggest that some animals, including at least one species of dinosaur, lived in southern polar regions well after they had become extinct elsewhere. Rich refers to these animals as ‘living fossils of the Cretaceous’. The Allosaurus was there 20 million years after it disappeared in North America. Labyrinthodonts, large carnivorous amphibians, may also have held on. Until a decade ago, based on finds in Germany, labyrinthodonts were thought to have died out at the end of the Triassic, about 208 million years ago. Recently, specimens from the Jurassic, between about 208 and 145 million years ago, have been reported from several places in Asia, as well as from single sites in Australia and Asia.
But younger remains of Early Cretaceous labyrinthodont fauna are common in the Strzelecki ranges. This extends their existence by at least another 25 million years, according to Rich. Curiously, labyrinthodonts are not found in the Otways – crocodiles apparently filled the same ecological niche. Vickers-Rich says the slightly warmer temperatures which prevailed when the Otway deposits were formed allowed the crocodiles to invade and displace the labyrinthodont.
DARK DAYS
When combined with finds from Alaska, the Australian deposits suggest that dinosaurs could survive many weeks of total darkness in near-freezing temperatures. If this is correct, it challenges the argument that darkness and cold caused by an asteroid impact wiped out the ancient reptiles. ‘The presence of dinosaurs near both poles was an enduring association, not a random event,’ says Rich.
In the mid-1980s, William Clemens from the University of California at Berkeley and Elisabeth Brouwers from the US Geological Survey found the plentiful remains of duck-billed dinosaurs called hadrosaurs on the Colville River at a site well within the Arctic Circle. Now Rich is working with Roland Gangloff from the University of Alaska at Fairbanks to organise the excavation of fossil deposits on the banks of the Colville, about 100 kilometres from Prudhoe Bay and within 30 kilometres of the Arctic Ocean. The deposits are from the Late Cretaceous, about 67 million years ago, just before the dinosaurs suddenly disappear from the fossil record.
The Alaskan dinosaurs are found today at about 70 degrees North, much closer to the latitude at which they lived and died, compared with the remains in southeastern Victoria. According to Rich, the mining methods developed at Dinosaur Cove will be useful in Alaska: ‘They’ve been digging in the summer, using techniques you would use in mid-latitudes, but I think that is dangerous. At that time of year, the ice that holds the river banks together is melting and the banks keep collapsing. When I was there in 1989 you could hear the rush of tonnes of mud sliding into the river every minute or two.’
Rich and Gangloff, who consulted miners in Alaska, agree that the excavation should be done in early spring when the ground is still solid. ‘A series of holes should be dug for explosives, the rock dislodged, and then scraped out – just like at Dinosaur Cove.’ If funding can be found, the work will begin next spring, right after the first full-scale expedition to the Strzelecki sites. If past experience is anything to go by, palaeontologists can expect some interesting finds to ponder.
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How to mine a dinosaur
Dinosaur remains have been discovered down a coal mine in Belgium, but the mine at Dinosaur Cove in Victoria is believed to be the first one excavated specifically for dinosaurs. The fossils at Dinosaur Cove are embedded in hard sandstones, siltstones and claystones that can only be freed using proper mining tools – jackhammers, drills and explosives.
Tom Rich, who leads the team of palaeontologists and volunteers at the site, has become a qualified mine manager. He insists that only expert mining engineers, who volunteer their services, lay the charges and supervise the blasts. Over the years, at a site within Dinosaur Cove called Slippery Rock, about 300 tonnes of rock have been removed and more than 60 metres of tunnels have been excavated, including two large underground chambers.
In 1991, 60 tonnes of concrete were poured to support a pillar of rock which for several years has prevented the collapse of two tunnels dug into the cliff face. The rock, expected to be rich in fossils, will be removed this year. The mining equipment, as well as the sand, screenings and cement used for the concrete, were taken to the site via a 305-metre long ‘flying fox’ – an aerial tramway on a cable. Rich estimates that because of the primitive techniques used, the bags of sand screenings were handled nine times each before the concrete was poured. ‘We have a real love of labour at Dinosaur Cove,’ he says.
Working in the area can be dangerous too. In 1990, a stormy sea dislodged a 20-tonne boulder onto the shore platform that was to be used as the staging area for the expedition. One year, Rich fractured a bone when he was thrown against a rock by a wave. The dinosaur hunters have not worked at night since a nocturnal wave ripped drilling equipment out of a tunnel – the gear was recovered later from rock pools.