The Illinois Department of Natural Resources is returning a fish called the alligator gar to the state’s rivers. Some people call the fish a living fossil. Experts believe the fish first appeared during the Early Cretaceous period more than 100 million years ago. Randy Sauer is an Illinois state fisheries biologist. He says the fish disappeared from the state’s rivers in the 1990s, although they have continued to do well in southern states. Sauer says biologists want to bring the fish back to northern rivers “because it is important to have top predators to balance the species below them,” he said. Sport fishermen like to try to catch the alligator gar. Alligator gar are the second-largest freshwater fish in North America.