Cetaceans (whales, dolphins, and porpoises) are generally classified into two groups: toothed whales (including dolphins and porpoises) and baleen or filter-feeding whales. However, recent molecular evidence suggests two alternative phylogenetic trees: one that indicates sperm whales are closely related to baleen whales or the alternative that sperm whales are more closely related to the common ancestor of all cetaceans. In a recent study, Nikaido et al. (2007) tested these alternative phylogenetic trees (hypotheses) using additional DNA sequences. a. Are sperm whales more closely related to baleen whales or dolphins?
b. Which group (dolphins, sperm whales, or baleen whales) do you predict will have more nucleotides in common with hippos?
c. Why do you think hippos are included in this tree? Are they the common ancestor to all whales?