At a remote and barren Sahara desert site in Niger, scientists have unearthed fossils of a new species of Spinosaurus, among the biggest of the meat-eating dinosaurs, notable for its large blade-shaped head crest and jaws bearing interlocking teeth for snaring slippery fish. It prowled a forested inland environment and strode into rivers to catch sizable fish like a modern-day wading bird — a “hell heron,” as one of the researchers put it, considering it was about 40 feet long and weighed 5-7 tons. The dinosaur presented a striking profile on the Cretaceous Period landscape of Africa some 95 million...