December 2004 - Materials Science Institute - University of Oregon

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Dinosaurs at the Top of the World During the Cretaceous period, some 75 million years ago, continental landmasses (orange regions in inset at bottom left) occasionally included a bridge of land, or isthmus, across what is today the Bering Strait. Dinosaurs probably walked across this stretch of land from Asia to North America. Some settled in the far north; others headed south. In present-day Alaska the author and other paleontologists search for the fossil remains of the creatures that made their home so close to the North Pole. One of the richest sites for B e r i n g S t r a i t Arctic Circle RUSSIA PACIFIC OCEAN North Pole ARCTIC OCEAN Landmasses 75 million years ago Wainwright B e r i n g S t r a i t Colville River Kaolak River Yukon River Aniakchak National Monument bones is Liscomb Quarry (top right), where fi nds include a group of juvenile duck-billed dinosaurs, or hadrosaurs (bones at bottom right), which probably died together, perhaps in a fl ash fl ood. Footprints of a small predatory dinosaur (middle right) from a nearby site on the Kaolak River appear white because of a silicone compound that is used to mold the ancient imprints. Another footprint (bottom center)—from the Aniakchak National Monument in southern Alaska—was molded and contoured to allow the scientists to identify and study it. Liscomb Quarry Kikak- Tegoseak Quarry Brooks Range ALASKA COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC. Anchorage Hadrosaur footprint from Aniakchak National Monument, with contoured cast CANADA Liscomb Quarry Dinosaur footprints near Kaolak River Upper armbones from three juvenile hadrosaurs at Liscomb Quarry CREDIT
of northern Alaska consisted of a mixed canopy that included deciduous conifers with an understory of fl owering plants, ferns and cycads. Today mixed coniferous forests occupy a wide but well-defi ned range of climates with mean annual temperatures from three to 13 degrees Celsius (37 to 55 degrees Fahrenheit), suggesting that the average yearly temperature for northern Alaska during the Cretaceous was similar. One of the striking aspects of the modern Arctic is the angle of sunlight and the length of the day—commonly, though mistakenly, referred to as six months of daylight and six months of night. In actuality, north of the Arctic Circle, darkness occupies a longer and longer part of each day until the winter solstice (December 22), when the sun does not rise. During the Cretaceous, northern Alaska was even farther north than it is today, and so the dinosaurs that lived there would have needed mechanisms to cope with both the cold and the dark. We do not know the full explanation of how they survived. It seems unlikely that a 10-meter-long (35-foot-long) hadrosaur dug a hole in the ground and went into hibernation. But during times of environmental stress, some animals can lower their 88 SCIENTIFIC AMERICAN DECEMBER 2004 COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC. CREDIT
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DINOSAURS OF THE ARCTIC ■ MASTERP
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December 2004 - Materials Science Institute - University of Oregon

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