The Age of Dinosaurs opened and closed with two of Earth's worst catastrophes
The Mesozoic began after the Great Dying, when perhaps 90 percent or more of marine species vanished, and ended with an asteroid strike off the Yucatan. In between, over roughly 186 million years, dinosaurs rose to dominance, birds branched off from them, flowers appeared, and Pangaea tore apart.
British geologist John Phillips coined the name in 1840 from Greek words meaning middle life, placing the era between the Paleozoic and the Cenozoic. It had earlier been called the secondary era. It runs from about 252 to 66 million years ago and splits into the Triassic, Jurassic and Cretaceous. The climate swung between warm and cool spells but was hotter overall than today, and gymnosperms such as cycads, ginkgos and araucarian conifers dominated the plant world for most of it.
The Triassic opened on a devastated planet, with deserts across Pangaea's interior and survivors such as Lystrosaurus roaming the land. By the Middle Triassic ecosystems had recovered, ichthyosaurs swam the seas, and the first dinosaurs and crocodilians evolved. Another extinction closed the period, possibly driven by flood basalt eruptions in the Central Atlantic region, clearing competitors and helping dinosaurs take over as the leading land vertebrates for somewhere between 135 and 150 million years.
The Jurassic was humid and tropical. Herds of sauropods such as Brachiosaurus and Diplodocus grazed fern prairies while Allosaurus hunted them, and the first avialans, including Archaeopteryx, evolved from small theropods. Mammals stayed small, under 15 kilograms, but diversified cleverly: Castorocauda swam and caught fish, Fruitafossor dug into insect nests, and Volaticotherium glided like a flying squirrel. Rising seas began opening the Atlantic.
The Cretaceous, the longest period, brought seasons back and saw flowering plants spread until they displaced conifers. Tyrannosaurus, Triceratops and Ankylosaurus shared the land, and mosasaurs ruled the oceans. Near the end, the Deccan Traps were pouring out volcanic gases when a large impactor created the Chicxulub crater 66 million years ago. That event erased all non-avian dinosaurs, along with pterosaurs, mosasaurs and plesiosaurs; estimates put losses at about 75 percent of life.
Source: Mesozoic
