More than 95 million years ago, a mighty river system roared through what is now the Moroccan Sahara, providing a home to one of the most unusual river monsters known to science, the predatory dinosaur Spinosaurus. Fully grown, the 50-foot-long, seven-ton beast stretched longer than an adult Tyrannosaurus rex and had an elongated snout similar to a crocodile’s that bristled with sharp, conical teeth.

Now, paleontologists plumbing these ancient sediments have found large abundances of those conical teeth at two sites in southeastern Morocco. In one bone bed, teeth from Spinosaurus outnumber those of other dinosaurs by roughly 150 to one. Because these rocks formed from river sediments, the discovery implies that Spinosaurus lost its teeth in the water far more