On a balmy Sunday morning in early March, I'm on a beach in southern Australia looking for ice—or at least traces of it. It's summer in the Southern Hemisphere, and most of the beachgoers sloshing through the rising tide or walking their dogs are wearing T-shirts and shorts. Tom Rich, a paleontologist at Museum Victoria in Melbourne, leads the way along the low, tawny cliffs that crowd the shoreline. Rich is 66, with a stubbly silver beard, sparse gray hair and slanting eyebrows that give his face a sad, world-weary look. He was raised in Southern California and Texas but has spent his professional life in Australia. During more than three decades down under, he's picked up Aussie citizenship and plenty of the country's colorful lingo, but his accent remains stubbornly American. "I sound like I just got off the plane," he says.

This part of the coast, known as Flat Rocks, is near the resort town of Inverloch, about a two-hour drive southeast of Melbourne through farms and woodland parched by more than a decade of drought. Rich stops next to a pile of rubble at the base of a cliff. "That's it," he says. Partly buried by flakes of battleship-gray rock is a telling geological formation. Tongues of dark tan sediment droop into the lighter-colored layer below. The formation is called a "cryoturbation" and was caused when once-frozen clay sank into an underlying layer of sand during a thaw long ago.

Snow and ice are rare in this part of Australia today. But evidence from Flat Rocks and other nearby sites confirms that a little over 100 million years ago, "it was bloody cold around here," as Rich puts it. Though about a third of Australia now lies within the tropics, back then the continent sat about 2,000 miles south of its current position, snuggled against Antarctica. Southeastern Australia probably had a climate similar to that of Chicago, if not Fairbanks.

All the more surprising, then, that dinosaurs thrived here at that time. Think "dinosaurs" and you probably conjure up behemoths trudging through sweltering swamps or torrid tropical forests. But Rich and other scientists working in Australia, Alaska and even atop a mountain in Antarctica have unearthed remains of dinosaurs that prospered in environments that were cold for at least part of the year. Polar dinosaurs, as they are known, also had to endure prolonged darkness—up to six months each winter. "The moon would be out more than the sun, and it would be tough making a living," says paleontologist David Weishampel of Johns Hopkins University.

The evidence that dinosaurs braved the cold—and maybe scrunched through snow and slid on ice—challenges what scientists know about how the animals survived. Although Rich wasn't the first to unearth polar dinosaurs, he and a few other paleontologists are filling in the picture of how these animals lived and what their environments were like. Recent research might also shed light on two of the most disputed questions in paleontology: Were dinosaurs warmblooded? And what killed them off?

Every year from late January to early March, Dinosaur Dreaming—the polar dinosaur project led by Rich—descends on the shore near Inverloch. The sound you hear as you walk up the beach toward the dig is the clinking of hammers on chisels. Kneeling around flat-topped beach boulders that serve as improvised workbenches, a dozen or so volunteers pound on lumps of gray rock. Several wear this year's fashion statement, a T-shirt that reads "Mammalia: Popcorn of the Cretaceous" and shows a bipedal dinosaur clutching two ratlike mammals in one paw and tossing another toward its gaping, toothy mouth.

Down in the "hole," a knee-deep gash near the waterline marked off by a circle of fluorescent pink construction netting, another group is using a rock saw and chisels to dislodge blocks the size of loaves of bread. These chunks will also go under the hammer.

At a folding table in the lee of the cliffs, Lesley Kool is triaging the finds brought in by the rock-breakers. Kool started out as a volunteer on Rich's first dino excavation in 1984. She knew little about dinosaurs, but she trained herself to be an expert preparator—the person who winkles fossils out of the rock without smashing them to dust—and developed a knack for identifying fossils. Now she runs the dig. She can tell you that the brownish chunk you hoped was the dinosaur find of the century is really a commonplace bit of fossilized turtle shell.

The crew she supervises includes a smattering of students, a retired literature professor from Tucson, a vacationing manager from an auto parts maker and the owner of an environmental cleanup service who can't stop bursting into song. Most of them come back year after year. They say they return for the camaraderie—and the chance of making a discovery. "It's an addiction for which there is no cure," says Nicole Evered, 68, who has worked on the Flat Rocks dig since it started.

Here the stereotypical image of the fossil hunter sprawled in the dust, unearthing a gigantic dinosaur bone with only a whisk broom and dental picks, doesn't apply. The fossils are too small, too fragmentary and too scattered. In more than 20 years of digging at various places in southern Australia, Rich and his crew have discovered only three articulated specimens, with bones connected as they were in life.

Most of the dinosaur bones they find at Flat Rocks, Kool explains, come from "hypsis" (pronounced HIP-sees), short for hypsilophodonts. These small, darting plant-eaters typically stood about as tall as turkeys. Their distinctive thighbones, which sport a downward-pointing spur, are easy to recognize. But this year's dig has also turned up some rarer finds, such as a thumbnail-size tooth from an as yet unnamed meat-eating dinosaur. One rock yielded a long, black fang that looks like an obsidian toothpick and may have come from a pterosaur, a type of flying reptile. And just two months ago, Rich's colleague Anthony Martin of Emory University in Atlanta announced that patterns in a 115-million-year-old layer of mud at Flat Rocks are dinosaur tracks. The 14-inch-long, three-toed footprints came from a type of meat-eating dinosaur called a theropod. Judging from the size and spacing of the prints, it must have stood about 12 feet high, making it the largest carnivorous dinosaur known to have lived there.

Promising fossils get wrapped in toilet tissue and newspaper for protection. Back at the museum, preparators will remove the encasing rock with tools that range from tungsten carbide needles to miniature, hand-held jackhammers powered by compressed air. Even unpromising chunks of rock will be pounded down to nuggets the size of sugar cubes; the team will check the bits for mammal jaws that are so small they could fit on a postage stamp.

It was the prospect of finding ancient mammal bones—not dinosaurs—that drew Rich to Australia. He was never a dinomaniac, not even as a child. What hooked his imagination, though, were the early mammals that scurried around at the same time as the dinosaurs. One illustration in a book he read as a boy portrayed the animals as snacking triumphantly on dinosaur eggs. Rich went with the evolutionary winners and studied fossil hedgehogs for his doctorate at Columbia University.

He landed in Australia in the early 1970s with no job and no intention of looking for one. His wife, Patricia Vickers-Rich, also a paleontologist, was in the country to follow up on her PhD research on fossil birds. But while thumbing through a newspaper "to get an idea what this country was about" he saw a help wanted ad for a curator at the local museum. He got the job and works there to this day. Rich and his wife—now a professor at Monash University in Melbourne and chief collaborator on the dinosaur research—stayed here because, he says, "the country was wide open" for studying the early evolution of mammals and birds.

In 1982, Rich met some museum volunteers eager to get their hands dirty at a dinosaur dig, but he initially resisted their pleas. He knew of a site 180 miles west of Flat Rocks that he had dubbed Dinosaur Cove after finding a few unidentifiable bone fragments there years earlier. Excavating there would require tunneling into cliffs—a dangerous proposition—with no guarantee of finding anything. But in 1984 he finally gave in, and within weeks the team found several dinosaur bones and a tooth.

For ten years Rich and a mostly amateur crew blasted, bored, picked and chiseled into the steep hillside. They dug two tunnels, each more than 60 feet long, and moved more than 600 tons of rock, much of it by hand. Rich says that "you wouldn't have to work that hard in Montana," which is famous for its dinosaur deposits and where the tectonic movements that hoisted the Rockies exposed bone-harboring rock strata. In contrast, Rich calls Australia, where dinosaur sediments are mostly buried deep, a "crappy country for dinosaur fossils."

By weight, the haul from the decade-long Dinosaur Cove dig was relatively small, about 100 pounds of fossils, and only traces of the mammals Rich covets—an arm bone and a shard of tooth. But the finds supplied clues about polar dinosaurs' metabolism and their strategies for weathering the long winters. They even provided a rare glimpse of the creatures' brains. Poring over the skeletons made Rich one of the world's experts on polar dinos.

At the time dinosaurs arose, around 220 million years ago, the earth's continents were fused into a single supercontinent we now call Pangea. It began breaking up around 200 million years ago, and Australia and Antarctica, which were still stuck together, stayed near the South Pole. When the fossilized creatures Rich studies were scurrying around, about 100 million years ago, southern Australia sat close to the bottom of the planet, and was just starting to pull away from Antarctica. (Australia's current position reflects that it has been inching northward "at the rate your fingernails grow," Rich says.)

During the animals' heyday in the early Cretaceous period, the sun didn't rise in southern Australia for one and a half to four and a half months every year. At the North and South poles, the gloom lasted for six months. Plant growth in these areas would have periodically slowed or stopped, potentially creating a food crisis for any dinosaurs that lived there. In more than 20 years of digging, Rich and his colleagues have found the remains of at least 15 species. For example, the knee-high hypsi Leaellynasaura amicagraphica (named for Rich's daughter, Leaellyn) once dodged predators at what is now Dinosaur Cove. Rich's son, Tim, got his name attached to another Dinosaur Cove denizen, the six-foot-tall Timimus hermani, which probably looked and ran like an ostrich.

Dinosaurs also thrived farther south. Antarctica hasn't moved much in the past 100 million years, stalling over the South Pole. Today, well-insulated animals and stubbly plants can survive the continent's brutal cold, at least close to the coast. But fossilized leaves and other plant remains suggest that during the dinosaurs' day Antarctica had a temperate climate. Judd Case of Eastern Washington University in Cheney says that Antarctic dinosaurs from the late Cretaceous period around 70 million years ago resembled those that lived in other parts of the world some 60 million years earlier. Case says this suggests that some kinds of dinosaurs hung on in Antarctica long after they had died out elsewhere. Perhaps Antarctica was an oasis for them as flowering plants spread across the rest of the world and outcompeted the pine tree relatives that warmer-climed dinosaurs ate.

William Hammer of Augustana College in Rock Island, Illinois, digs at an elevation of 13,000 feet on the slope of Mount Kirkpatrick, about 400 miles from the South Pole. He has pried out the bones of Cryolophosaurus ellioti, a 22-foot-long meat-eater with a bony crest curving up from its forehead like a cowlick. He has also found fossil evidence of a prosauropod, an ancestor of enormous dinosaurs such as Brachiosaurus and Apatosaurus.

At the opposite end of the globe, on Alaska's North Slope, Anthony Fiorillo, a paleontologist from the Museum of Nature and Science in Dallas, has been exhuming bones from dinosaur graveyards along the Colville River. Although northern Alaska wasn't as cold 70 million years ago as it is today, winters would still have brought snow and ice. Back then, sharp-toothed relatives of Tyrannosaurus rex stalked the 35-foot-long, duck-billed dinosaur Edmontosaurus. The surprise from these finds, Fiorillo says, is that the same types of dinosaurs lived in Alaska as in toastier environments farther south, such as Montana and even Texas. So far, he hasn't unearthed any dinosaurs that appear to have lived only in frosty climes.

Dinosaurs had two choices when winter arrived—tough it out or try to escape. The question of how dinosaurs survived the polar cold has gotten entangled with the broader question of whether the ancient beasts were warmblooded (endothermic), like modern birds and mammals, or coldblooded (ectothermic), like modern reptiles. In a cold environment, endotherms keep their bodies warm enough for muscles to flex and nerves to fire by generating heat through their metabolism. Ectotherms, by contrast, warm their bodies by absorbing heat from their surroundings—think of a lizard basking on a rock. Endothermy isn't necessarily better, notes David Fastovsky of the University of Rhode Island. Endotherms have the edge in stamina, but ectotherms need much less food.

The prize discovery from Rich's Dinosaur Cove excavation suggests that Leaellynasaura stayed active during the long polar winters. A two-inch-long Leaellynasaura skull the color of milk chocolate is the closest to a complete dinosaur skull the team has found. The base remains partly embedded in a disk of gray rock scored by numerous grooves where Kool meticulously exposed the fossil with a fine needle. Enough of the bone is visible for Rich to analyze the size of the eye sockets. Hypsis generally had big eyes, but Leaellynasaura's are disproportionately large—perhaps so they could capture more light during the protracted murk of polar winters. Moreover, the back of the same skull has broken off to expose a mold of the brain, known as an endocast. Rich found that the dinosaur had bulging optic lobes, parts of the brain that process visual information. Leaellynasaura's optic lobes are larger than those from hypsis that lived in non-polar environments, suggesting that it had extra brainpower to analyze input from its big eyes.

Similarly, Fiorillo and Roland Gangloff, a retired paleontologist from the University of Alaska, have found that the small meat-eater Troodon was much more common on the North Slope of Alaska than farther south. Troodon might have gained an advantage over the other carnivorous dinosaurs in the north because it also had large eyes and a hefty brain, perhaps useful for hunting all winter long.

Other dinosaurs might have migrated south for the winter (or north, if they lived in the Southern Hemisphere). Rich says his dinosaurs would have made unlikely travelers. They were small, and an inland sea would have blocked their path to warmer climes. But Edmontosaurus, from Alaska's North Slope, is a better candidate for seasonal migration. Adults were about the size of elephants, so they would not have been able to crawl under rocks when temperatures fell. Rough calculations suggest that by ambling at about 1 mile per hour—"browsing speed" for animals of that size—herds of Edmontosaurus could have journeyed more than 1,000 miles south in three months, says paleobotanist Bob Spicer of the Open University in Milton Keynes, Britain. Such a migration would have taken them out of the "zone of darkness" and into areas where plants might have still been growing.

For his part, Fiorillo doubts it. He and Gangloff contend that juvenile Edmontosaurus grew too slowly to have tramped long distances. They couldn't have kept up with a herd, so the animals must have stayed put, regardless of temperatures. This kind of back-and-forth might be dizzying, but it's how science moves ahead, especially in paleontology, where researchers have to draw conclusions from small numbers of often-fragmentary fossils.

The dinosaurs had an impressive run. They settled every continent, grew bigger than any other land animals and lasted for more than 150 million years. And then they vanished. Their demise has spawned more than a little speculation about its cause. Scenarios range from disease or competition with mammals to the flyby of an as-yet-undetected companion to the sun, a kind of death star.

Most paleontologists have accepted another extraterrestrial killer, an asteroid more than six miles wide that socked Earth 65 million years ago. It gouged a crater more than 100 miles wide on what is now the Yucatán Peninsula in Mexico. According to the leading scenario, the impact threw huge amounts of dust and other debris into the atmosphere, blocking sunlight and sinking the Earth into darkness for weeks or even months. A global disaster certainly struck at the time, according to overwhelming fossil and geological evidence. As Fastovsky and Weishampel write in The Evolution and Extinction of the Dinosaurs, "the world's oceans were virtually 'dead'" as photosynthesis by plankton ceased and marine food webs unraveled. The dinosaurs died, while the ancestors of today's mammals, birds and reptiles hung on.

Paleontologists disagree about what the existence of polar dinosaurs says about the asteroid-winter scenario. Fiorillo says he is skeptical of it because "dinosaurs in Alaska were doing just fine in conditions just like that." He argues that climate changes caused by shifts in circulation of the atmosphere and oceans probably did in the dinosaurs.

But Rich says that the lives of polar dinosaurs can help researchers understand why dinosaurs went extinct after the impact. The catastrophe had to have been long and severe enough to kill off the dark- and cold-adapted animals. "You can't just have it [darkness] for a month and do the job," he says.

But Fastovsky says that polar dinosaurs tell us nothing about the animals' demise because we don't know whether these particular species were even alive at the end of the Cretaceous period. Rich's Australian dinosaurs were long extinct by the time the asteroid hit. Whether the dinosaurs on the North Slope of Alaska were alive is uncertain, he says; researchers have found no fossil layers there from the very end of the Cretaceous period.

For polar dinosaurs to provide more definitive evidence on dinosaur metabolism and extinction, we'll need more fossils. This year Rich embarked on a dig on Alaska's North Slope, his first. It's expensive work, and it took him 18 years to line up the funding necessary to transport, on a single-engine Otter plane and snow machines, his field party and their equipment, which included rock drills, chainsaws, jackhammers and explosives.

Rich and his advance team prepared the site on the Colville River, about 375 miles north of Fairbanks, in late March and early April, when the temperatures sink to minus 40 degrees Fahrenheit. They hired a miner to drive a horizontal shaft into the riverbank just above a layer of dinosaur fossils. Working at that time of year sounds crazy, Rich admits, but it's actually easier to dig a tunnel when the ground is frozen solid.

In August, the full ten-member team walked into the tunnel and extracted fossils from the floor. They are still sorting the bones, but Rich has already identified one notable find: a type of pachycephalosaur, a plant-eating dinosaur with an unusually thick skull that has been found only once before, also in Alaska. It might be the first known dinosaur that lived exclusively in the Far North, more evidence that the ancient beasts endured even the coldest and darkest days.

Mitch Leslie was a dinosaur fanatic as a child and studied reptiles before becoming a writer. He lives in Portland, Oregon.

Books
Dinosaurs of Darkness, by Thomas H. Rich and Patricia Vickers-Rich, Indiana University Press, 2000
Dinosaurs of Australia and New Zealand and other animals of the Mesozoic Era, by John A. Long, Harvard University Press, 1998
The Evolution and Extinction of the Dinosaurs, 2nd edition, by David E. Fastovsky and David B. Weishampel, Cambridge University Press, 2005