Why Dinosaurs Were Like Tuna, Great Whites, and Echidnas

Fifty years ago, dinosaurs lumbered across our screens like the slow-moving, shambling oafs they were thought to be. Now, they stride and sprint. They’re portrayed as active animals, often lithe and agile.

This popular makeover was inspired by a scientific one. Scientists used to believe that dinosaurs, like modern-day reptiles, were cold-blooded ectotherms. That doesn’t mean their blood was literally cold, but that they relied on the environment to heat their bodies. Many lines of evidence challenged this view, suggesting instead that some dinosaurs were warm-blooded endotherms like mammals and birds: they generated body heat by burning energy at a much greater rate than most reptiles.

This debate about dinosaur metabolism—were they ectotherms, endotherms or something in between?—is one of the

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