ABSTRACT
Apes, humans, monkeys, and prosimians such as lorises, bush babies, and lemurs make up the 234 species of primates, a mammalian order with distinctive common features indicating descent from a single ancestor: a small, tree-dwelling mammal that subsisted on fruit and insects. All primates share behavioral and anatomical characteristics, but humans and chimpanzees are particularly close. Elephants and rhinoceroses are ungulates. Their teeth adapted for their plant diet, with strong molars for grinding. Preyed upon by big cats, wolves and other carnivores, ungulates rely on various methods of defence. Some are large, many are swift, and others grow horns or antlers. They often mass in large herds to minimize the risk to an individual. Dolphins, porpoises and whales are known as cetaceans. They are aquatic mammals that must come to the waters surface to breathe through blowholes. There are about 80 species of cetaceans. Dolphin species include pilot and killer whales, and river dolphins living in South America and Asia.
