Deinosuchus crocodile. Computer artwork of Deinosuchus underwater, shown with a human for size comparison. Deinosuchus is an extinct crocodile that lived in the upper Cretaceous period. It is thought to have reached up to 12 metres in length. It was an ambush predator that hunted fish and dinosaurs. Deinosuchus fossils have been found in both freshwater and saltwater habitats.