Up for bid is one fossil mosasaurs tooth. . You will receive one tooth randomly selected with all being in good to very good condition. Mosasaurs are a family of enormous, extinct, marine dinosaurs (reptiles) that ruled the seas for 25 million years during the Cretaceous period. Some species of Mosasaurus could reach lengths in excess of 50 feet and where the apex predator in nearly every part of the seas during their time. Great for necklaces, natural science gifts or to just talk about, Stock photo. Nice fossil. Great natural science gift.