The temperature at the south pole this morning was 20 degrees below zero Fahrenheit, with blowing snow. But 70 million years ago, the waters around Antarctica were probably balmy -- with temperatures in the 50s.
New evidence of that dramatic temperature change comes from the discovery, announced today by the National Science Foundation, of the skeleton of a reptile that swam in what is now the Southern Ocean.
The fossil is of a plesiosaur, a long-necked animal with four fins. The new find is of a baby, not even five feet long from head to tail. It is one of the best-preserved skeletons of its type ever discovered.
"It's really a spectacular find," said Judd Case of Eastern Washington University, one of the leaders of the expedition that went to the Antarctic to scout for fossils. "We've never found anything this complete."
Digging the fossil up was no easy task. It was buried in the dry, windswept wastes of Vega Island, Antarctica. Vega Island is just off the Antarctic Peninsula, the part of the continent that comes closest to South America.
Today, the land is rocky and barren. Fossils go undisturbed there, mainly because it's so hard for anything else, including scientists, to survive. Winds howl at 70 mph for days on end, even in summer, with temperatures so cold that exposed water freezes in just minutes.
But 70 million years ago, Vega Island would have been heavily forested, with some of the world's first flowering plants. The steep slope where the plesiosaur was found was likely near a shoreline.
Plesiosaurs were technically not dinosaurs. Scientists say they had more in common with modern sea turtles and snakes.
"All we know is they lived and died in an environment that was much different than ours today," said Jim Martin of the South Dakota School of Mines, who joined Case on the expedition.
Plesiosaurs have been found in England and Scandinavia. They may have been plentiful throughout the world's oceans during the Cretaceous Period, when tyrannosaurrus rex roamed the land.
But fossils are hard to come by, not only because plesiosaurs were marine creatures, but because the preservation of any fossil is almost a matter of luck.
When living things die, most decay quickly. On a rare occasion, they get caught in a rock slide, or the mud at the bottom of a pond or lake. All too often, whatever kills them crushes them.
In the case of this young creature, death was probably swift -- and violent. The scientists speculate that this plesiosaur may have been caught in the blast of a volcano, smothering it, but also protecting its remains from water and air.
"We think that this poor baby may have had a very difficult end, caught in a very major volcanic eruption, and that this volcanic eruption was very explosive and catastrophic," said Martin.
Such accidents probably happened to a tiny fraction of all living things -- and in most cases, that's the only way scientists can ever know that they existed.
The fossil, protected in plaster, was taken to South Dakota to be cleaned and studied. Its existence now will probably be somewhat more sedate than its life was.
Scientists say the plesiosaur was probably a carnivore, living off the prehistoric fish and other marine reptiles that shared the ocean with it. Stones were found in the area of its stomach; whether they acted as a ballast or helped digestion, it's unlikely anyone will ever know. The animal's long neck probably made fishing easier; it could move its head without having to move its whole body.
But the animal probably had to fend off larger predators -- including the ancestors of the modern shark, which already existed but had trouble competing with larger sea creatures that are now extinct.
"Life for a young plesiosaur, like a young sea turtle, was a little bit tough," said Martin. "You're just trying to survive and get big enough so people will leave you alone. Not any different from being on the school playground."