Final answer:
The evidence for cetaceans being part of artiodactyl mammals comes from fossils like Rhodocetus with artiodactyl-like ankle bones, phylogenetic trees showing shared ancestry with other artiodactyls, and genetic data from the Mammalian Supertree supporting a close evolutionary relationship.
Step-by-step explanation:
Evidence for Cetacean Artiodactyl Relationship
The evidence for the placement of Cetacea within the artiodactyl mammals is multifaceted, involving paleontological, anatomical, and genetic data. One significant piece of evidence comes from the fossil record, particularly the discovery of the aquatic mammal Rhodocetus, which possesses a distinct type of ankle bone that is characteristically found in artiodactyl land animals. Further support is provided by phylogenetic trees, used to trace evolutionary relationships, which show that cetaceans, including various species of whales and dolphins, are descended from even-toed ungulates and share a common ancestry with other artiodactyls such as hippos, cows, sheep, camels, and pigs. This suggests a close evolutionary relationship, indicating a terrestrial origin for these marine mammals.
Additional evidence comes from ancient cetaceans like Pakicetus and Rhodocetus, with both demonstrating hindlimb presence in varying degrees, linking them further to land-dwelling ancestors. This phylogenetic evidence is supported by genetic studies, such as the Mammalian Supertree derived from DNA comparisons, revealing cetaceans as part of the wider artiodactyl group. Combined, these findings paint a clear evolutionary picture of the terrestrial origins of cetaceans, and their subsequent adaptations for aquatic life, highlighting the process of natural selection and evolutionary change.