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The Q? Blog

Who Was Boss Before the Dinosaurs?

by Devin Reese -- Sep 15, 2015
Devin Reese, smiling

Devin is the lead digital science writer for the Q?rius website. She writes and gathers media for the Smithsonian Science How? webcast series,...

Large hippo-like mammal forerunner ("Placerias") that lived, and died off, during the Triassic. National Park Service Image.
Large hippo-like mammal forerunner ("Placerias") that lived, and died off, during the Triassic. National Park Service Image.

The Jurassic witnessed a world populated by dinosaurs -- giant plant-eaters munching their way through ferns and conifer forests, while large carnivores chased them down for lunch. At the height of the Age of Dinosaurs, they were found on every continent, flourishing in the warm environments of the time.

But, dinosaurs were not always so prominent. Fossil evidence shows that they arose about 230 million years ago during the Triassic period, but remained scarce as other reptiles took center stage. Many mammal forerunners, such as the large plant-eater Placerias, prospered. Huge crocodile-like animals like Smilosuchus were the top predators of the Triassic.

Paleontologists who study the fossil record have discovered that something big happened 200 million years ago that radically changed life on land and in the sea, paving the way for dinosaur diversification and prominence. What happened was so momentous that it caused more than half of all life on Earth to go extinct. The large crocodile-like reptiles that had dominated the landscape were eradicated, as were many of the mammal forerunners.

Find out more about the events that opened the door for the Age of Dinosaurs. Watch a “Smithsonian Science How” video on How Fossils Explain the Rise of Dinosaurs on the Q?rius website. Paleontologist Dr. Hans Sues from the National Museum of Natural History discusses and answers questions. Get teaching resources to support your experience.

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