Mammals

Mammals Characteristics Integument & Derivatives Skin is thicker than other vertebrates Epidermis – thinner, protected by hair Dermis – thicker Glands Sweat Glands Eccrine glands Secrete a watery fluid, draws heat away when evaporated Apocrine glands Secrete milky fluids that dry on skin to form a film Scent Glands Used for communication, marking territory, warning or defense, attracting mates Sebaceous Glands produce a substance called sebum which is responsible for keeping the skin and hair moisturized. Mammary Glands Secretes milk

Mammals Characteristics Integument & Derivatives Hair – two kinds of hair forming their pelage (fur coat) Coarse & longer guard hair for protection sometimes modified to form defensive spines (as in porcupines, in which the cuticular scales elongate to form barbs that make it difficult to remove imbedded spines), Dense & soft Underfur made up of wool (ever-growing hairs), fur (relatively short hairs with definitive growth), and/or velli (down or fuzz). Mammalian embryos (including humans) also are often covered with a pelage, called lanugo, which is a kind of a fuzz.

Mammal Characteristics Food & Feeding Some have highly specialized diets, others thrive on diversified diets Teeth reveal the life habit of a mammal Incisors – simple crown/sharp edges for snipping/biting Canines – long conical crowns, specialized for piercing Premolars & Molars – compressed crowns for shearing, slicing, crushing, or grinding. Most grow two sets of teeth Deciduous (or milk) teeth – temporary set Permanent teeth – when the skull has grown large enough to support a full set Only incisors, canines & premolars are deciduous; molars are never replaced

Mammal Characteristics Feeding Specializations Insectivores Shrews, moles, anteaters, bats Feed on small invertebrates – worms, grubs, insects Have teeth with pointed cusps Herbivores Feed on grasses & other vegetation Browsers & grazers – horses, deer, antelope, cattle, sheet Gnawers – rodents, rabbits Canines are absent or reduced Carnivores Foxes, dogs, weasels, wolverines, cats Feed mainly on herbivores Omnivores Pigs, raccoons, bears, most primates Feed on plants & animals

Mammal Characteristics Movable eyelids & fleshy external ears Four – chambered heart Highly developed brain Endothermic Internal fertilization Embryos develop in a uterus Young nourished by milk from mammary glands

Reproduction Most mammals have a definite mating seasons Females fertility is restricted to a specific time (estrous cycle) Three different patterns of reproduction Monotremes Egg-laying (oviparous) mammals Duck-billed platypus – embryos develop for 10-12 days in uterus. Thin leathery shell secreted around embryo before eggs are laid. Hatch underdeveloped after 12 days. Feed on milk after they hatch

Reproduction Marsupials Pouched, viviparous mammals They give live birth, but they do not have long gestation times give birth very early and the young, helpless embryo, climbs from the mother's birth canal to the nipples, it grabs on with its mouth and continues to develop, often for weeks or months depending on the species.

Reproduction Placental mammals Placental mammals all bear live young, which are nourished before birth in the mother's uterus through a specialized embryonic organ attached to the uterus wall, the placenta. Length of gestation is longer than marsupials Larger the mammal the longer the gestation Mice – 21 days Cats & Dogs – 60 days Elephants – 22 months