Fifty miles north of the coast, a gentle breeze wafts beneath tangled canopies and over still waters. Sequoia, cypress, and monkey puzzles tower in interlocking trunks over a wide backwater bayou, their branches encrusted with colonies of fern, moss, and creeping fig. Gentle slopes are covered in trees similar to modern beech and walnut, their roots tangled in flowering thickets and piles of decaying leaves. Insects buzz in lazy trails between the flowers. Fruits tumble to the forest floor or plop into the bayou, accompanied by the whoop and honk of toothed birds. Unseen things — striking garfish, perhaps — splash against the surface, sending concentric rings questing out across the reflected forest. The air smells of earth, pollen, and rot, and its humid weight presses down in a suffocating blanket.



This is the temperate Appalachian rainforest, a place known only from scattered leaf impressions, petrified wood and coal, and water-bound bodies. The canopies form a broad, unchanging belt around the continent, with only minimal differences deep into the interior. During the wet season, swollen rivers overflow their banks and spread across the lowlands in a network of backchannels, replenishing ponds and drying swamps. Even the high ground — a relative term here — is cut by narrow, gushing creeks. Plant families that in our day are separated by thousands of miles — jungle ferns and tulip trees, ficus and spruce — grow here in interconnected groves from Montreal to Tuscaloosa. Yet despite the richness of these forests, they seem to support only a few types of large dinosaurs.

To understand why this is the case, it helps to look at the intersection of geology and evolutionary theory. Of the many processes driving the evolution of distinct species, one of the most powerful is geographic diversity and isolation: Animal populations that can’t easily interbreed tend to grow more distinct over time. In Laramidia, the growing Rocky Mountains carve the landscape into isolated provinces, leading to a cornucopia of distinctly horned, armored, duck-billed and carnivorous dinosaurs. But Appalachia’s mountains are dying. By the late Cretaceous, they’ve been reduced to low foothills and slumping tablelands, and it will be many millennia before tectonic processes raise them to their current heights. The ability to move across the entire continent without much effort means that the same sorts of plants and animals are found across the entire landmass. There are only a handful of big herbivores and a solitary big carnivore. The lower ranks of small dinosaurs and birds are doing somewhat better, but can’t match their western comrades in terms of distinct species. The continent is a warning of a coming state of affairs. In 12 million years, dwindling dinosaur diversity will culminate in the catastrophic Cretaceous extinction.



But for now, while biodiversity is low, the creatures that do live here are numerous, successful, and quite distinct from their western neighbors. The continent is a refuge for the archaic and the bizarre, and several million years of isolation have led to ecological relationships that can only be guessed at.

In the shadows of the high boughs, one of the habitat’s primary architects is currently at work, a hundred feet from the bayou’s edge. A duck-billed dinosaur, Lophorhothon, is stripping the nearby vegetation with single-minded thoroughness. Thirty-six feet long and heavy as a bull elephant, she scoops up leaves and ferns, shoulders over saplings, and scrapes orange mushrooms off overturned logs. Everything is mashed by batteries of teeth and swallowed into a bulging crop. She is eating for 10 — several miles away, she and the other females in her loose group have shallow nests filled with crowds of striped, peeping young. For the first month of their life, the chicks are dependent on their parents for food. So, while the males guard against predators, the females spread out on foraging missions.



Appalachia is the ancestral home of the hadrosauroids, the group of herbivorous dinosaurs to which Lophorhothon belongs, and the eastern branch of the family has largely kept the appearance of its forebearers. Unlike their western kin, they generally don’t have elaborate head crests.