The fossil record provides a highly variable and incomplete geological record of life on earth. Fossils from the equatorial zone are particularly rich in terms of their evolutionary history. Fossilized bones from this region often suggest very similar phenotypes for organisms as far apart as East Asia and southern Europe. These bones seem to have been deposited by organisms who shared a common ancestor. The similar structure and phenotypic indicators of the fossils suggests that at some point the common ancestral species migrated across different regions and settled in different parts of the world. Over time, the ancestral species evolved into several unique species, each adapting to its particular environment.