Smithsonian Magazine · People & society

Five Ways the Dinosaur World Differed From Ours

The Earth during the Age of Dinosaurs (Mesozoic Era, 252-66 million years ago) was significantly different from today's world, not just in its inhabitants but also in its environments and geology.

The flora of the dinosaur era lacked flowering plants, featuring instead large relatives of ginkgoes and horsetails, alongside extinct lineages. Forests were often kept open by large herbivores. Flowering plants became more common in the Cretaceous period, but modern dense forests only emerged after the dinosaurs' extinction.

The Mesozoic Era was largely a global hothouse, with periods of extreme heat causing ice-free poles and high sea levels. The early Triassic was particularly hot due to volcanic activity, with average global temperatures around 89°F, compared to today's 59°F.

Geologically, most of Earth's landmass was united as the supercontinent Pangaea during the early dinosaur age. Plate tectonics gradually broke Pangaea apart, separating continents and creating new oceans throughout the Jurassic and Cretaceous periods.

Ocean levels fluctuated, with seas repeatedly encroaching on landmasses. Marine life was also distinct, featuring abundant ammonites, crinoids, and spectacular marine reptiles like ichthyosaurs, plesiosaurs, and mosasaurs, which have no modern equivalents.

Mammals existed alongside dinosaurs but were often very different. Early mammals, or mammaliaformes, were diverse, some laying large clutches of eggs, while others, like multituberculates, had smaller litters and nursed their young. Placental mammals, similar to humans, only became prominent after the dinosaurs' extinction.

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