The first four-legged vertebrates did not grow up like tadpoles after all. That idea has shaped the story of life on land for decades. Early tetrapods, the ancient animals that gave rise to mammals, birds, reptiles, and amphibians, were widely thought to begin life much like modern amphibians. They were believed to hatch into a larval stage and later transform into adult bodies through metamorphosis. But newly described fossils of baby tetrapods suggest that picture is wrong. Writing in Science, researchers report that some of the earliest known hatchlings from the fish-to-tetrapod transition lacked the hallmark features of amphibian larvae, especially external gills. Instead of passing through a frog-like tadpole stage, these animals appear to have developed more directly. “When a lot of us were in high school, we were taught this simplified story of evolution: that some fish evolved into amphibians, and some of those amphibians evolved into reptiles, and some of those reptiles evolved into mammals. And our study shows that this basic underlying premise, that the first four-legged vertebrates grew up like …