Class Mammalia

Characteristics

Hair of Mammals

• All mammals have hair.
• Some have more than others.
• Hair: a collection of nonliving cells filled with filaments of the protein keratin
• Two types of hair:
• Underhair: soft, insulating layer next to skin
• Guard hair: coarse, longer, found over the under hair
• Various functions:
• Beavers: waterproof, never gets soaked to the skin
• Camouflage
• Whiskers: sensory nerves, permit them to detect objects in their path
• Porcupine: barbed quills that protect them from predators

Leopards use their fur as camouflage

Porcupines use theirs for protection

Limbs of Mammals

• Usually have two pairs of limbs used for locomotion
• Look different in different animals
• Bats: elongated fingers connected by thin membranes for wings
• Moles: shovel like limbs (dig around 4 m/h)
• Whales: paddles for swimming

Whales use their front limbs as paddles

Lions use their front paws to help catch their prey

Moles use their paws as shovels

Digestion of Mammals

• If something is edible, there is probably some mammal that eats it.
• Mammals eat grass, leaves, fruits, seeds, bark, tree sap, microscopic organisms, blood, honey, invertebrates such as insects and snails, and vertebrates, including other mammals.
• A variety of teeth:
• Incisors: flat, thin teeth in the front of the mouth, used in gnawing or biting.
• Canines: rounded, pointed teeth towards the front of the mouth, used for tearing
• Molars: usually thick, squat teeth in the back of the mouth, used for grinding and chewing
• Carnivores usually have enlarged canine teeth.
• Gnawing animals have large incisors.
• Herbivores cut the foliage with the incisors and chew with molars.
• Omnivorous such as monkeys and bears have well-formed teeth of each type.
• Some animals have special structures or processes to process their food.
• Those that eat plants:
• Chew the cud
• Special enzymes
• Compartments in the stomach

Respiration and Circulation

• Oblong spongy lungs in the upper chest cavity.
• Separated from abdominal organs by diaphragm
• Air drawn into lungs by contraction of diaphragm
• Air passes down throat, through larynx (voice box)
• 4 chambered heart
• Complete separation of oxygenated and deoxygenated blood
• Circulatory system similar to man’s
• Expend energy to maintain constant body heat
• Mammals that live in hot climates have mechanisms to keep cool
• Those in cold climates have mechanisms to keep them warm.

Polar bears have proportionately small heads

Elephants take mud baths

Response

• The cerebrum—the center of intellect and instinct—dominates the mammalian brain, making mammals the most intelligent animals.
• Also used for memory 
• Many express emotions such as fear, anger, contentment, excitement, and happiness.
• Sensory organs are similar to those of man, but sensitivity is different.
• Bats hear better
• Dogs smell better

Reproduction

• Most mammals have young that develop internally, nurtured by a placenta.
• Interface between mother and offspring through which gases, nutrients, and wastes are exchanged.
• These exclude marsupials (pouched mammals) and monotremes (egg layers)

Placental Mammals 

• Female mammals paired ovaries produce and release ova. Guided through a tubular oviduct toward the uterus.
• When a female’s ova are ready to be fertilized the animal enters a period called estrus or “heat”
• Various odors are released by the female at this time to attract the male.
• The male’s testes produce sperm. Internal fertilization takes place. The sperm is carried in a liquid to the egg where it fertilizes it in the oviduct. Before it has reached the uterus, the zygote has divided several times.
• First few cells of the animal are implanted in the uterine wall. 
• Placenta is formed of some uterine cells and embryonic cells.
• Rich blood supply
• Exchange of nutrients, gases, wastes
• The two blood supplies don’t actually mix
• Blood vessels form an umbilical cord
• The length of pregnancy is called gestation.
• Gestation varies depending on species. Generally the longer the gestation the more developed the baby.
• Rats: 21 days
• Horses: 335 days
• After baby is born, mother supplies milk from mammary glands
• Many mammals train their young to hunt, select fruit, build shelters, etc. before they leave the family.

Marsupials: The Pouched Mammals

• Kangaroos, koalas, and other marsupials produce young without a placenta. Fertilized egg begins growing and dividing within the uterus, but does not implant itself.
• Nourished by a small yolk sac. When the yolk sac is depleted, the baby crawls out of uterus.
• It must then crawl from there to the pouch. It can then start to feed on milk. Completes its development in the pouch. 

Monotremes: Egg-Laying Mammals

• Exception to many mammalian characteristics. 
• Single hole for digestive, excretory, and reproductive systems.
• Lay eggs and incubate them like birds.
• Young drink milk, but they don’t have nipples. Milk empties onto the skin and the young lap it off the fur.