For a list of genera, species, and subspecies, see the Appendix. F. Fossil record. Modern forms of both odontocetes and mysticetes appear in the fossil record five to seven million years ago. These ancestors of present-day whales had teeth and some adaptations for an aquatic life. The relationship between early whales and modern whales is unclear due to a poor fossil record.
Scientists agree that ancestors of baleen whales probably had teeth.
Early baleen whales appeared around 30 million years ago. By 25 million years ago, early members of the right whale family appeared. The modern genus Balaena appeared about 5 million years ago. Members of the rorqual family appeared about 15 million years ago, including the modern genus Megaptera. The modern genus Balaenoptera appeared about 5 to 10 million years ago.