Because Cetacea are so highly specialized for their aquatic lifestyle, they bear little resemblance to their artiodactyla ancestors. They have nearly hairless, fusiform bodies. They lack hind limbs except for tiny internal pelvic vestiges, and the forelimbs are modified into streamlined flippers. The tail bears a flattened fluke. In addition, cetacean skulls are highly modified so that the nares are located on the top of the head. On the other hand, most artiodactyla are specialized for cursorial locomotion, with long, hoofed limbs, and they lack the extreme aquatic specializations found in cetacea. Most cetartiodactyls are relatively large animals, but there is an enormous range of body sizes in this group. Blue whales, Balaenoptera musculus, are the largest animals on earth, growing over 27 meters in length and weighing over 190,000 kg, whereas the smallest artiodactyla, the lesser mouse deer (Tragulus javanicus), is just 45 cm long and weighs 2 kg. Many species of cetartiodactyls exhibit sexual dimorphism, with males larger than females or vice versa. Also, male artiodactyla often bear antlers or large horns, and some male cetartiodactyls (narwhals (Monodon monoceros), tragulidae, and suidae) bear large tusks. (Nowak, 1999; Rice, 1984; Simpson, 1984)
- Nowak, R. 1999. Walker's Mammals of the World, vol. II. Baltimore and London: The Johns Hopkins University Press.