Cetartiodactyls

Cetartiodactyls is a clade of mammals that unites the toothed and baleen whales with the even-toed ungulates. The group comprises Cetacea (whales, dolphins, and porpoises) and Artiodactyla (even-toed hoofed mammals such as cattle, sheep, goats, deer, pigs, camels, and hippos). Molecular and fossil evidence support a close relationship between whales and hippopotamuses, which is why many classifications treat Cetartiodactyla as a single clade rather than separate orders.

Within Cetartiodactyla, Cetacea is divided into two living subgroups: Mysticeti (baleen whales) and Odontoceti (toothed whales). Artiodactyla includes diverse families, most of which are terrestrial, though hippos are semi-aquatic. Hippos are also the closest living relatives of whales within the clade, indicating a common semi-aquatic ancestry in the lineage.

Cetaceans have adaptations for aquatic life, including forelimbs modified into flippers, a vestigial pelvis, a horizontal tail fluke, and nostrils positioned on the top of the head as blowholes. They breathe air and exhibit complex social and sensory adaptations for living in marine environments. Artiodactyls, in contrast, are typically hoofed mammals with an even number of toes; many are ruminants with a four-chambered stomach, though not all Artiodactyla are ruminants.

The clade’s origins trace to early Paleocene or early Eocene times. The earliest whales evolved from terrestrial artiodactyls, with transitional forms such as Ambulocetus documented in the fossil record. The hippo–whale relationship is supported by multiple lines of evidence, reinforcing the unity of Cetartiodactyla.

Cetartiodactyls include economically important domestic species (cattle, sheep, goats, pigs, camels) and ecologically significant marine mammals that face threats from hunting, habitat loss, and climate change.