Seven other species are extinct, prehistoric species known from fossils. They contain some limestone rocks showing abundant marine fossils. Most of these Precambrian fossils are microscopic bacteria or microfossils. The area is rich in dinosaur fossils. Attenborough spent his childhood collecting fossils, stones, and natural specimens. The island is one of the most important areas in Europe for dinosaur fossils. The paleontological evidence consists of changes in the geographical distribution of fossils. None of the Ediacaran fossils had hard body parts like skeletons. Vertebrates are known from both body fossils and trace fossils. The earliest fossils of ostrich-like birds are Paleocene taxa from Europe. The sites include Sterkfontein, one of the richest sites for hominin fossils in the world. Some other "Plesiosaurus" fossils are from later Sinemurian rocks. This makes some corals useful index fossils. The latter contain well-preserved, freshwater fossils. Preserved tracks and burrows are examples of trace fossils (also called ichnofossils).