In July 2014, researchers looking for fossil turtles in southern Utah’s public lands found hints of a “monstrous murderer”: the ankle bone of a tyrannosaur named Teratophoneus. Within hours, they had brushed through the sand between pinyon junipers and found the jumbled remains of multiple Teratophoneus—all of which seemed to have died in the same place, at the same time.

Scientists unveiled the site to the world in a study published last Tuesday in the scientific journal PeerJ, suggesting tyrannosaurs congregated in social groups. “Dinosaur behavior, dinosaur ecology, is probably always going to turn out a little more complex than we think at any given time,” says lead study author Alan Titus, a paleontologist with the U.S. Bureau of