Dinosaurs under the Aurora

1. The Arctic Setting

1 1 THE ARCTIC SETTING The Arctic coastal plain is crisscrossed by a host of meandering rivers that drain the northern slope of the rugged ancestral Brooks Range to the south. The rivers are pregnant with organic-rich sediment and rush headlong to the northern sea, being fed by melting snowfields and the common cloudbursts that sweep in from the Western Interior Seaway to the north and east. Large herds or aggregates of duck-billed dinosaurs move along river banks feeding on dense “gardens” of mud-loving horsetail rushes that have sprung forth from their subterranean rhizomes into the reawakening sunlight.1 Monodominant patches of drought-resistant ferns are interspersed with clumps of herbaceous angiosperms and grasses on small ridges and levee slopes.2 Stacks and tangles of lichen and moss-encrusted logs and branches form along the edges of sloughs and oxbow lakes. Large logs of deciduous conifers, such as Parataxodium from forests deep in the interior, have mixed with smaller ones that had spent their lives closer to where they now lie. The rushes and ferns grow very rapidly due to the long, warm, lengthening days. The largest concentrations of duckbills are located along the margins of shallow sloughs, floodplain lakes, ephemeral ponds, and river banks with smaller groups strung out along the crowns of larger river levees. The rich bounties of aquatic plants that occupy the floodplain lakes and ponds are the targets of groups of duckbills like Edmontosaurus, who can use their spoonbill-like jaws to “shovel” in rhizome mats and clusters of plants similar to water ferns, duckweed, and water lilies. Some small groups of duckbills venture into upland coniferous forests and come upon larger groups of ceratopsians such as Pachyrhinosaurus. The ceratopsians and duckbills selectively partake of mixes of deciduous conifer trees such as Parataxodium and Podozamites. Some hadrosaurs and ceratopsians feed on the leaves of these trees as well as on an understory of ferns, scattered cycadophytes (Nilssoniocladus), and the rarer clusters of mistletoe and sandalwood. Individual ceratopsians such as Pachyrhinosaurus select fruits such as Ampelopsis and Cissites.3 On occasion, they take in insects and snails crawling over the leaves—a serendipitous protein treat. Only adults and subadults venture deep into the denser wooded areas and upland forests where Troodon and other gracile predators can hide and wait in ambush. These woodlands are too dangerous for the more vulnerable juveniles to feed in. The Arctic Coastal Plain circa Seventy Million Years Ago Dinosaurs under the Aurora 2 Hours later, the sky turns to an angry gray, filling with roiling masses of water-laden clouds that are being driven southward against a dark wall of mountains. Torrents of rain sweep down the mountain slopes and are channeled northward to the sea. A 100 miles away, the groups of Edmontosaurus are totally absorbed by their search for food, unaware of the rush of water that is coming their way. A large group of Edmontosaurus, a few standing conspicuously above the rest, appears at the top of a large levee and stops to feed on the lush plant smorgasbord before descending to the edge of the fast-flowing river. While their fellow travelers are dining, a dozen of the larger individuals approach the river. Hesitating for just a moment, they plunge in, making enormous splashes as they push against the strong current. The rest of the group is now dominated by juveniles that are half to one-quarter the size of their adult and subadult attendants. Just as the adults finally reach the opposite shore and struggle up the opposite embankment, a larger group of adults and subadults catch up. Anxious to follow their leaders, they take the plunge, and this spurs the juveniles to follow. The water is shallow enough that most of the juveniles can just touch bottom. Just as this mix of adults, subadults, and juveniles makes it a quarter of the way across the river, a four-foot-high pulse of water reaches the struggling group, greatly increasing the strength and velocity of the current. Most of the larger animals struggle across, making ever-widening arcs, and end up hundreds of feet farther downstream than those who first crossed. The juveniles, who are only one year old or younger, are quickly exhausted by the struggle against the current and are unable to touch bottom. The first youngsters flail about wildly and begin to drown as they are carried down river. The remainder of the nursery that is onshore continues to plunge...