Dinosaurs did not appear first. For hundreds of millions of years, life had already been evolving in the oceans and on land. Immediately before the age of dinosaurs came the Permian Period, about 299 to 252 million years ago, a time of vast forests, amphibians, insects and many kinds of reptiles and their relatives.

A world of synapsids

Some of the most memorable Permian animals belonged to a branch called synapsids. This branch is part of the much older evolutionary family tree that eventually includes mammals. One famous synapsid was Dimetrodon, recognized by the tall sail on its back. Despite often appearing beside dinosaurs in popular pictures, Dimetrodon was not a dinosaur. It lived tens of millions of years before the first dinosaurs.

Later synapsids included therapsids, a diverse group with features that became more mammal-like over time. They shared the Permian landscape with amphibians, early reptiles, insects and plants such as ferns and seed plants. Evolution was already producing a rich variety of bodies and ways of life; it was not waiting for dinosaurs to begin.

The Great Dying

At the end of the Permian, about 252 million years ago, Earth experienced the largest known mass extinction in its history. The Permian–Triassic extinction reshaped life in the sea and on land. Scientists study evidence for major volcanic eruptions and severe environmental changes as important parts of the story. Ecosystems took a long time to recover.

Then came the Triassic

The Triassic Period followed the extinction. Mammal relatives and many kinds of reptiles lived in the recovering ecosystems. The first dinosaurs appear in the fossil record during the Triassic, roughly 230–240 million years ago, depending on how scientists interpret the oldest fossils. They were one branch among many, not yet the rulers of every habitat.

So what came before dinosaurs? A long, branching history of animals—and a changing planet. The Permian world reminds us that dinosaurs were one chapter in the story of life, not its beginning.

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