In hot pursuit of polar dinosaurs
Some hibernated. Some grew large eyes. All adapted to the extreme winter. Now their secrets are being unearthed.
INVERLOCH, AUSTRALIA — Standing on a low bluff overlooking the Pacific Ocean, paleontologist Tom Rich pauses. "This is pretty civilized for a fossil dig," he admits.
He and his team sleep in a resort town. They spend hours on the beach slathered in sunblock. When it gets too hot, they cool off in a tide pool nearby.
Yet, this is hardly a vacation. The team is sifting for clues about some of the least-understood creatures of prehistory: polar dinosaurs.
Some 115 million years ago, long before Tyrannosaurus Rex was a glint in anybody's eye, dinosaurs roamed what is now southeastern Australia, which at the time lay well within the Antarctic Circle. Now, their remains - unearthed on this narrow stretch of beach two hours southeast of Melbourne - are contributing to the most species-rich collection of polar dinosaur fossils in the world. And they're opening new windows on how these ancient animals adapted to frigid climates, and why some survived in one of the world's most isolated regions while their kin had died out elsewhere.
The site also challenges the ingenuity of archaeologists who, instead of scratching for fossils in an arid wasteland, pack up every time the tide comes in, then pump out their dig and begin again.
Indeed, discovery of the surprising diversity of creatures that existed here between 115 million and 105 million years ago - particularly the dinosaurs - is perhaps the most important result to come out of the work done in the region, says Hans-Dieter Sues, associate director for research and collections at the National Museum of Natural History in Washington.
"The fact that this very diverse assemblage of vertebrates was living in what at the time were really high latitudes has important implications," he says. "Dinosaurs were coping with this extreme environment. This flies in the face of the now-ancient notion that dinosaurs were just overgrown reptiles" in tropical settings.
At the time, this region had a climate closer to that of Fairbanks, Alaska, than to, say, tropical Cairns, Australia. Dr. Rich's site was part of a vast river-laced valley formed as Australia and Antarctica began to part company. Thus, some of the region's creatures show evidence that they hibernated or otherwise slowed their body processes in the winter. Others appear to have been active all year, their eyes larger than others' in order to function in winter darkness.
From the work here at Flat Rocks, outside Inverloch, and at Rich's previous site at Dinosaur Cove, west of Melbourne, it appears that Australia served as a retirement home for over-the-hill dinosaurs. "These polar environments are places where animals could go and be safe, and last when they were being wiped out at lower latitudes," says Rich, curator of vertebrate paleontology at Melbourne's Victoria Museum. But new species "also could be generated here."
The coexistence of dinosaurs and mammals in such extremes is raising questions about just how wildly the climate varied and the range of mechanisms creatures developed to cope with such changes.
As evidence of the wide swings, Rich takes a visitor to a thick petrified tree trunk jutting from the rock shelf, suggesting that a temperate forest thrived here at one point. Just 200 yards away, he shows soil layers at the base of the bluff that indicate permafrost, evidence for tundra-like conditions at another stage.
"We don't know if some of the animals we find lived here all the time, or whether they migrated in and out as climate shifted from warm to cold periods," Rich says.
The Flat Rocks site also is yielding insights into the evolution of ancient mammals. For example: Until now, many paleontologists held that the complex bone structure within a mammal's ear probably evolved from a common ancestor. But it now appears that this "middle ear" evolved independently among different groups of mammals, based on a 115 million-year-old jawbone Rich and his colleagues unearthed here. Researchers say the results, reported in the Feb. 11 edition of the journal Science, provide a striking example of similar features evolving separately in groups of mammals only loosely related.
Rich's work, undertaken with his wife, Patricia, a paleobiologist at Monash University in Melbourne, is part of a broader effort to piece together the history of life in one of the world's most isolated continents.
For understanding the history of life on Earth, "Australia is a very significant region," says Dr. Sues, whose museum is part of the Smithsonian. Its geological history, which has led to its isolation, has left Australia with a unique assemblage of animals. Thus, the continent has been a mecca for evolutionary biologists, who have been keen to trace the lineages and early history of its plants and animals as far back as the fossil record will allow.
That same geological history, however, has been a bane to paleontologists trying to study the period Rich's work covers. In much of the country, conditions for fossil preservation are poor. Erosion over millions of years has erased much of the oldest fossil records, as has water leaching through porous soils.
Rich notes that the first dinosaur fossil found in the state of Victoria, in which Inverloch lies, appeared in 1903. It was taken from the face of a seaside bluff only a mile or so from Flat Rocks. The next major dinosaur discovery didn't surface until 1978.
Rich's team began working at what came to be known as Dinosaur Cove in 1984. The site yielded more than 8,000 bones over 10 years. As that dig was winding down, a storm hit the coast, stripping the sand from the surface of the vast stone platform that gives Flat Rocks its name. The storm exposed the fossil-bearing layer and 20 to 40 bones. This marks their 12th season at the site.
The location poses unique challenges. Each day is a race against the tide. The fossils come from rock pulled from a jack-hammered pit 8 feet wide by 16 feet long and 3 feet deep. When the tide rises, the excavation team covers the pit with weighted tarps. These keep out most of the sand, but none of the water. Once the tide recedes, excavators must pump out the pit and empty it of sand before they resume work. The pace is quick; the team only has six weeks to work each summer.
The work takes place on an open beach, so it's not unusual to see people stroll through the site walking dogs or hunting for shells. One year, a group of clean-cut men in starched overalls walked by, recalls Nichole Evered, a longtime volunteer. Seeing the sizable number of people huddled over boulders, one asked Ms. Evered what she was doing.
"Breaking rocks," she replied.
"Voluntarily?" he asked, incredulously.
"He was part of a prison work party," she explains.
With each split in a sample, team members peer through magnifying glasses looking for telltale fossils, some no bigger than half of a pinkie's fingernail. Two volunteers bring a potential fossil to Lesley Kool, who prepares the fossils for archiving at the museum. She gives it a quick look-over. "Sorry, guys. It's just a bit of rust."
But the team will not go back to the house empty-handed. Two men have freed a large chunk of promising stone from an outcropping near the main pit. It yields a bonanza, including what looks to be a small leg bone.
The day's haul prompts Rich to proclaim as the tide comes in: "It's been a good day."