The oldest fossils are remains of marine organisms that populated the ... bones, shells, or wood -- were preserved. Fossils can be formed in several ways. Buried bone and shell contain tiny ...

Sharks have ruled the Earth’s oceans for 400 million years. Recent research on fossil shark teeth has discovered an ...

12. Dwellings and structures: Some marine worms secrete calcareous tubes in which they live. The fossil is not of the organism, but of a structure it built. Even more elaborate dwellings have been ...