ABSTRACT
Across all vertebrate lineages mammals stand out for their adaptability. They are endothermic and at birth are nourished by milk secreted by the mother’s mammary glands. Mammals have an upright posture that is reflected in the bones of the limbs and girdles. The mandible is composed of a single element, the dentary, and forms a unique joint with the base of the skull. Teeth exhibit a division of labor; some like canines are used for piercing, whereas molars are for cutting or grinding. Mammals have three tiny bones in the middle ear (an evolutionary consequence of their unique jaw articulation), whereas other tetrapods have only one. These and other characteristics and their precursors are to varying degrees available in the fossil record. With them we can trace the roots of modern placental mammals that appeared in the early Cenozoic back to their synapsid heritage in the late Paleozoic.
Southern California’s mammal fauna consists of one marsupial, the non-native opossum, and 124 species of placentals with the following orders and families represented: shrews and moles (2 families, 5 species), bats (3 families, 22 species), rabbits (1 family, 3 species), rodents (7 families, 53 species), carnivores (6 families, 21 species, and 3 others historically extirpated), perissodactlys (1 family, 2 species both introduced), artiodactyls (3 families, 3 species one of which is introduced, and 1 family and species historically extirpated), and 15 species of cetaceans including both Mysticeti (baleen whales) and Odontoceti (toothed whales).
