Arctic dinosaurs raise questions.

The 65-million-year-old bones of at least three dinosaur species and two prehistoric reptiles have been recovered from a site in the Alaskan tundra by a team of researchers from the University of California at Berkeley and the University of Alaska at Fairbanks.

Although the magnetic orientation of rock in the area indicates that the site, near Prudhoe Bay, was at least as far north when the dinosaurs lived as it is today (70[deg.] N latitude, fossils and other geologic evidence suggest that the site was a coastal swamp with a subtropical to temperate climate. Temperature rarely, if ever, dropped below freezing, says William Clemens, the Berkeley paleontologist who led the expedition. Such a mild climate was possible in spite of annual periods of darkness because the earth's climate was much more "equable" -- or uniform -- in those days, explains Fairbanks paleontologist Carol Allison.

Clemens says the dinosaurs' presence at such high latitudes challenges a recent theory that all dinosaurs became extinct after asteroids smashed into the earth and raised dust clouds that darkened the planet for weeks (SN: 4/21/84, p. 250). According to the theory, the darkness and subsequent falling temperatures caused plants to die, leaving the warm-blooded dinosaurs chilled and starving. Since fossil findings indicate that both young and old dinosaurs were at the Alaska site in great numbers and over a long period of time, says Allison, "you have to consider the possibility that, unless they engaged in some huge mass migration every year, they were dark-adapted."

Last week, Clemens took the bones back to Berkeley, where he hopes to determine whether the dinosaurs belong to previously unidentified species. If they are different from dinosaurs already known from lower latitudes, that would support the idea that they did not migrate and were dark-adapted. In the unlikely event that they did migrate, he says, "it's a little mind-boggling the distances they'd have had to move, but we just don't know what their biology was like."

The most common dinosaur at the site is the plant-eating duck-billed dinosaur, or hadrosaur, which walked on its hind legs and stool as tall as 15 feet. The paleontologists also found two carnivorous dinosaurs -- a small birdlike one and the teeth of something like Tyrannosaurus rex -- as well as the bones of a large crocodile-like reptile and an aquatic reptile known as the pleisosaur.

Although the dinosaur bones were first discovered at the site by a Shell Oil Co. employee in 1961, Shell did not reveal the find until last year, say the researchers.