Whole Ichthyosaur

Photograph by O. Louis Mazzatenta

Ichthyosaurs, like this one found in Guizhou Province, China, evolved in the early Triassic, nearly 250 million years ago. Early specimens were reptilian in form—in fact, "ichthyosaur" means "fish-lizard"—but quickly evolved a dolphinlike shape. They went on to become one of the top ocean predators and thrived for 160 million years before going extinct in the mid-Cretaceous, about 25 million years before the dinosaurs died out.