"We think there are so many here because they were well-adaptedmaybe pre-adaptedto the high latitudes, and they came here and thrived," said Rich.
There are several characteristics that made the hypsilophodontid well suited to polar conditions. Their optic lobes are enlarged compared to dinosaurs found closer to the Equator, which would enable them to see better in the dark. Thomas and Patricia Rich estimate that the polar dinosaurs living in southeastern Australia spent about three months a year in darkness.
"But it wasn't complete darkness; remember the moon," said Rich. "During that time of the year you see the moon from half full to full, back to half full, so you do have some light."
There has been some speculation as to whether polar dinosaurs lived in the high latitudes during the warmer months, and then either migrated to warmer climes or perhaps hibernated through the colder months.
The researchers think both scenarios are unlikely. The bones of most dinosaurs show lines of arrested growth, meaning that at some time, probably annually, their growth slowed significantly. This is not true for the hypsilophodontids, which implies they remained active year round, and didn't hibernate, said Rich.
Migration is also unlikely, they say.
"When you're talking about migrating long distancesthe caribou, for instance travels around 2,000 kilometers (1,250 miles)you're talking about an animal the size of a horse or a cow. The hypsilophodontid is a very small animal; if they flew, that would be one thing, but for a little animal on foot, it's too far and doesn't make sense energetically," said Rich.
Alaska's North Slope
The dinosaurs on Alaska's North Slope wouldn't need to hibernate or migrate because the temperatures were much warmer than they are today. Researchers estimate that from about 90 million to 65 million years ago, temperatures on the North Slope probably ranged from a maximum of 55 degrees Fahrenheit (13 degrees Celsius) to a minimum of 36 to 46 degrees Fahrenheit (2 to 8 degrees Celsius).
However, it was cold enough that a lot of animals seen at slightly lower latitudes are missing from the North Slope fossil record.
"When you look at the vertebrate composition in the Late and Middle Cretaceous on the North Slope, you're not seeing the total vertebrate record that you see with dinosaurs in Montana and Alberta," said Gangloff. Truly cold-blooded animals like lizards, newts, turtles, and crocodilians, which are superabundant farther south are missing, he said. The lack of these fossils could provide some clues to dinosaur physiology.
"The concept of cold-blooded versus warm-blooded has been so oversimplified that it makes physiologists grit their teeth and want to bite someone," said Gangloff. "The range of dinosaurs is huge; a sauropod is 70 feet (21 meters) long; you have other dinosaurs that are the size of birds."
Rather than thinking in black and whitean animal is either cold-blooded or warm-bloodedphysiologists think in terms of an animal falling into a range between being physiologically endothermic (body temperature is controlled internally) or ectothermic (body temperature is controlled by external factors). It's likely that there are wide metabolic variations among dinosaurs, and polar dinosaurs can begin to shed some light on the issue.
Establishing a polar fossil record is not easy; the logistics required to hunt for fossils in the isolated corners of the Earth are far more costly than at mid-latitudes. But there is tremendous potential in the Northern Hemisphere for more work to be done, and the researchers are anxious to take the next step.
"We've established that dinosaur fossils found in polar regions are not a fluke and that dinosaurs were capable of adapting to a huge range of environmental conditions," said Gangloff.
One way to learn more about polar dinosaurs is to tunnel into the permafrost using the same tunneling machines used for gold mines, underground subways, and for oil.
Understanding how dinosaurs adapted to a climate that was quite a bit warmer could give us an idea of our own future, said Rich.
"If we're going to muck about with the environment, and make the Earth a much warmer place than it is today, studying extinct biotas will give us some kind of indication about the world we'll be passing on to our grandchildren," he said.
Recent National Geographic News stories on dinosaurs:
Study Paints New Picture of Dinosaur's Nose
Skeleton of New Dinosaur "Titan" Found in Madagascar
"Tidal Giant" Roamed Coastal Swamps of Ancient Africa
"Feathered" Fossil Bolsters Changing Image of Dinosaurs
Oddly Angled Teeth Make Masiakasaurus Stick Out
Additional dinosaur resources from National Geographic:
Paul Sereno: NG explorer-in-residence and dinosaur hunter
Destinations: Dinosaur National Monument
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