Final answer:
The recent theory on whale phylogeny identifies a close evolutionary link with even-toed ungulates, especially hippos, based on vestigial structures and genetic evidence. Fossil records of early whale ancestors and genetic analysis have both contributed to understanding their transition from land-dwelling to aquatic life.
Step-by-step explanation:
The recent theory of the phylogeny of whales suggests that these marine mammals share a closer evolutionary relationship with even-toed ungulates and in particular with the hippopotamus, despite their superficial resemblance to fish due to convergent evolution. Evidence supporting this includes fossil records exhibiting vestigial hindlimbs in early whale ancestors like Pakicetus and Rodhocetus, which imply a terrestrial origin. Moreover, recent genetic analysis has further solidified this relationship as modern whales share genetic similarities with these terrestrial ancestors.
Whales, as part of the order Cetacea, have undergone significant evolutionary changes transitioning from land to sea, resulting in the loss of functional hindlimbs and adaptations suited for an aquatic environment. Their phylogenetic trees continually evolve with new discoveries that increasingly highlight their terrestrial ancestry. At one point in their evolutionary history, cetaceans transitioned from possessing limbs conducive for land, like their ancestral even-toed ungulates, to developing flippers and other adaptations necessary for life in aquatic environments.