<p>Because <span class="taxon">Cetacea</span> are so highly specialized for their aquatic lifestyle, they bear little resemblance to their <span class="taxon">artiodactyla</span> 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 <span class="taxon">artiodactyla</span> are specialized for cursorial locomotion, with long, hoofed limbs, and they lack the extreme aquatic specializations found in <span class="taxon">cetacea</span>. Most cetartiodactyls are relatively large animals, but there is an enormous range of body sizes in this group. Blue whales, <span class="taxon"><em>Balaenoptera musculus</em></span>, are the largest animals on earth, growing over 27 meters in length and weighing over 190,000 kg, whereas the smallest <span class="taxon">artiodactyla</span>, the lesser mouse deer (<span class="taxon"><em>Tragulus javanicus</em></span>), 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 <span class="taxon">artiodactyla</span> often bear antlers or large horns, and some male cetartiodactyls (narwhals (<span class="taxon"><em>Monodon monoceros</em></span>), <span class="taxon">tragulidae</span>, and <span class="taxon">suidae</span>) bear large tusks.<span> (Nowak, 1999; Rice, 1984; Simpson, 1984)</span></p> <p><strong>Other Physical Features: </strong>Endothermic; Homoiothermic; Bilateral symmetry</p><p><strong>Sexual Dimorphism: </strong>Sexes alike; Female larger; Male larger; Ornamentation</p>
- Nowak, R. 1999. Walker's Mammals of the World, vol. II. Baltimore and London: The Johns Hopkins University Press.