For more than 100 years, researchers assumed that dinosaurs were like giant lizards: sluggish reptiles that spent most of their day basking in the sun. This image changed when we started to realize that dinosaurs were far more similar to birds than to modern-day lizards. Today, researchers agree that birds are technically dinosaurs — the only ones to have survived the mass extinction 66 million years ago. Yet, if that's true, why aren't birds cold-blooded like most modern-day reptiles?
The answer is straightforward: Most dinosaurs were probably warm-blooded, too.
