Things got pretty crowded in western North America about 75 million years ago. Back then, the region was an island less than one-third the size of today’s North America but hosted as many as eight species of herbivores that weighed a ton or more—a number unseen in today’s ecosystems and almost unprecedented at any time in the fossil record. Perhaps the dinos were just slow eaters, or maybe the ecosystems were exceptionally productive, researchers thought.
But a new analysis of fossils found in southern Alberta suggests that the giants got along because they ate different things, a trend called “dietary niche partitioning” that didn’t put them in direct competition with each other. In an ecological study broader than any other for dinosaurs of this era, researchers looked at a dozen different aspects of the skulls and jawbones of dinosaurs from 12 groups of species representing three major lineages of megaherbivores: horned ceratopsians (left), duck-billed hadrosaurs (browsing on trees in background at center right), and the group that includes ankylosaurs and nodosaurs (second from left and at right in foreground, respectively).