From Laura Klappenbach,
Your Guide to Animals / Wildlife.
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Cetaceans
Cetaceans (Order Cetacea) are marine mammals that includes toothed whales and toothless, filter-feeding (baleen) whales. Cetaceans are a unique and highly-specialized group of mammals with hairless bodies, flipper like forelimbs, and reduced back limbs that are located within the body wall (vestigal).

Hoofed Mammals
Hoofed mammals are classified into 2 orders, 13 families, and about 244 species. Mammals in this group include horses, rhinoceroses, tapirs, pigs, hippos, camels, deer, giraffes, and cattle. The two orders of hoofed mammals are the Perissodactyla (the odd-toed hoofed mammals) and the Artiodactyla (the even-toed hoofed mammals). Hoofed mammals are terrestrial herbivores.

• Order Perissodactyla: The odd-toed hoofed mammals include animals such as horses, zebras, rhinoceroses, and tapirs. Horses and zebras belong to the Family Equidae and exhibit great running speed and endurance and have a solid hoof on each foot. Rhinoceroses belong to the Family Rhinocerotidae. Rhinos have thick, plates of bare skin, and short, stout limbs. They have an ancient, almost reptile-like appearance. Tapirs are moderately-sized mammals with a pig-like appearance. They inhabit forests and even spend much time hiding in water evading predators.
• Order Artiodactyla: The even-toed hoofed mammals include animals such as pigs, boars, hippos, camels, llama, deer, elk, pronghorn, giraffe, okapi, yak, and American bison.

Rodents
Rodents are highly successful group of mammals that includes 30 families and over 1700 species. Rodents have worldwide distribution and live in a wide variety of environments such as terrestrial, semiaquatic, tree-dwelling, and underground habitats. They have acute senses of hearing and smell. Some species are nocturnal and have large eyes that enable them to see better in the dark.

• Squirrels and Relatives: Squirrels and their relatives belong to the Suborder Sciuromorpha. This group includes not only squirrels but also beavers, chipmunks, marmots, prairie dogs, and gophers.
• Mouselike Rodents: Mouselike rodents belong to the Suborder Myomorpha. This group includes mice, rats, voles, lemmings, hamsters, gerbils, and jerboas.

Seals and Sea Lions
The pinnipeds—the group of mammals that includes seals, sea lions and the walrus—are well-adapted to aquatic lifestyles. Pinnepeds belong to the Order Pinnipedia, a group of mammals composed of three families and about 34 species. The pinnipeds' streamlined bodies and flipperlike limbs enable them to swim with ease. Pinnipeds breed on land, and when doing so, often establish and guard territories on beaches.

• Monk Seals: This shy, reclusive group of seals feeds on fish, eels, sardines, and octopus. There are three species of monk seals, the Mediterranean monk seal, the Hawaiian monk seal, and the Caribbean monk seal. The Mediterranean and Hawaiian monk seals are endangered while the Caribbean monk seal is feared extinct.
• Walrus: The walrus is a social pinneped, gathering on land in large numbers. The walrus eats shellfish, shrimp, and fish and inhabits arctic waters.