back to Grade 6+ Fossils by: Julianne M., Grade: 6+ When dinosaurs became extinct some of them became fossils,fossils are formed when a animal decays and a sediment covers them and makes a mold.Other types of fossils are called trace fossils,petrified fossils and amber.Petrified fossils are just like petrified wood.Amber fossils are formed when a insect gets traped in tree sap and then it hardens.Fossils can be found all over the world. back to Grade 6+