Fossil Overview Fossils are the remains of a prehistoric animal or plant that has been covered in earth and preserved in the ground. Many fossils are found in sedimentary rocks. Technically there is no orgamc material left in the fossil because the bone has been transformed into a mineral. There are different types of fossilizations. A Mold fossil is when all the original material compnsmg an organism decays and leaves behind its shape in a rock, and over time the shape is filled in by rocks and minerals. Another type is called a compression fossil, where an organism's remains are intact, but its chemical make up has been altered over time. Trace fossils are left behind footprints or indentations, eggs, or even feces, while resin fossils are insects or small animals that have become trapped in amber which is formed from hardened tree sap. Oddly enough there are living fossils, these are living animals that resemble other creatures from the fossil record. To be a living fossil the animal has only recently been found alive or has no close living relatives. One of the first prehistoric fossils was that of a plesiosaur. The plesiosaur fossils were discovered in 1821 near Lyme Regis by Mary Anning. Another early paleontologist was Richard Owen who created the name "dinosaur," meaning terrible lizard. French naturalist Georges Cuvier was the first. scientist to compare ancient animals to modern animals. Paleontology is an ever changing scientific field, some of the most important discoveries were made in the last few years. American paleontologist Jack Horner discovered the first dinosaur eggs in the western hemisphere in the 1970s. In 1990 the most complete T-Rex skeleton was found and is named "Sue" after her discoverer Susan Hendrickson. 55 .