Mammals All Materials © Cmassengale

Main Characteristics of mammals:

• Endothermy - maintain high, constant body temperature through their metabolism
• Pelage - hair or fur made of protein called keratin covering all or part of the body for insulation & camouflage
• Four chambered heart ( two atria & two ventricles) keep oxygenated & deoxygenated blood from mixing; double circulation

Mammal Heart

• Mammary glands in females are modified sweat glands that make milk containing sugars, proteins, & fats to nourish young
• Single jawbone
• Specialized teeth for biting, cutting, & chewing
• Highly developed brain (large cerebrum)

• Diaphragm - muscle below lungs that aids respiration
• Most are viviparous (live birth)
• Uterus in females where young develop
• Placenta lines uterus & provides nutrients and gas & waste exchange for developing young
• Have sweat glands for cooling & scent glands for attracting mates & marking territories

Mammal Ancestors:

• Fossil records show mammals arose from group of reptiles called therapsids at the end of the Paleozoic era
• Therapsids were endotherms with specialized teeth like mammals

Therapsid

Early Mammals:

• First mammalian fossil found in Mesozoic era (hair, single jawbone, specialized teeth, & endothermic)

• Early mammals were small, shrew like, insect eaters that had large eye sockets making them probably nocturnal

• When dinosaurs became extinct, new habitats & food supplies opened up for mammals

• "Age of mammals" occurred during Cenozoic era

• Oviparous (egg laying) monotremes evolved first

Echidna	Platypus
Monotremes

• Viviparous (live birth) marsupials with incomplete uterine development appeared next & then placental mammals 

Tasmanian Devil	Armadillo
Marsupial	Placental

Specializations of the mouth & digestive system:

• Single jawbone
• Incisors - specialized, chisel like front teeth for biting & chewing
• Canines - pointed teeth or fangs behind incisors to help grip, puncture, & tear prey
• Bicuspids - teeth with two points behind the canines used to shear & shred food
• Molars - flattened back teeth to grind & crush
• Baleen - thin plates in the roof of the mouth of some whales that strain food from water
• Microorganisms living in the gut help some mammals digest cellulose from plants
• Hoofed mammals (cows, sheep, giraffes...) have a four-chambered stomach with bacteria living in the first chamber or rumen
• Cud - digested food in the rumen that is regurgitated, swallowed, & then chewed again to break down plant cellulose
• Caecum - stomach chamber in elephants, horses, & rabbits that contains bacteria to digest cellulose

Adaptations for Endothermy:

• High demand for oxygen
• Right & left sides of heart separated by septum so oxygenated & deoxygenated blood don't mix
• Left side of heart pumps blood to lungs & back (pulmonary circulation)
• Right side of blood pumps oxygenated blood to body cells (systemic circulation)
• Diaphragm - sheet of muscle below lungs that moves up & down in chest to change air pressure so gas moves into & out of the lungs
• Alveoli or air sacs in the lungs are surrounded by capillaries and increase the surface area for the absorption of oxygen
• Hair or fur and a fat layer insulates and prevents heat loss

Nervous System Adaptations:

• Largest vertebrate brain
• Cerebrum surface is folded to increase surface area without increasing volume
• Cerebrum controls sensory organs, coordinates movement, regulates behavior, & is responsible for memory & learning
• Have five major senses --- vision, hearing, olfaction (smell), touch, & taste
• Bats, whales, dolphins, porpoises  use echolocation (bouncing off of high frequency sounds) to navigate & find prey  

Reproductive Adaptations:

• Each of the 3 mammal groups --- monotremes, marsupials, & placentals--- has a unique reproductive pattern
• Monotreme females lay 1-2 leathery-shelled eggs containing yolk & incubates them with her body heat

• Young monotremes are small & partially developed at hatching so depend on mother for protection and milk from mammary glands
• Marsupials have short development period inside of the mother & newborns must crawl to the mother's pouch or marsupium after birth, attach to a nipple for milk, and finish developing 

Mother Kangaroo & "Joey"

• Placentals are the largest group of mammals
• Gestation (period of development inside mother) is longer in placental mammals
• Nutrients, wastes, gases exchanged through membrane lining uterus called the placenta

Order Monotremata:

• Oviparous
• Not completely endothermic (lower body temperature & it fluctuates)
• Have a cloaca where wastes, eggs, & sperm are emptied
• Includes duck-billed platypus & spiny anteaters or echidna

Echidna	Platypus
Monotremes

• Live only in Australia & New Zealand
• Platypus:
  1. Waterproof fur
  2.Webbed feet
  3. Flattened tail for swimming
  4. Flat, sensitive, rubbery muzzle used to root for worms & crayfish
  5. Digs a den in bank of river to lay eggs
  6. Female curls around eggs & incubates them
  7. Newborns lick milk from nippleless mammary glands    
• Echidnas:
  1. Terrestrial
  2. Coat of protective spines
  3. Long snout to probe ant hills & termite nests
  4. Incubate eggs in a brood pouch on female's belly

Order Marsupialia:

• Found in New Guinea, Australia, & the Americas
• Dominate animal in Australia due to lack of competition from placental mammals
• Known as pouched animals
• Pouch called marsupium
• Viviparous (live birth)
• Tiny, immature young must crawl to mother's pouch after birth
• Young attach to mammary gland nipple to nurse until able to survive outside of pouch
• Includes opossum, kangaroo, wombat, & koala

Koala & baby	Opossum

Placental Mammals :

• Young carried in uterus & nourished by placenta
• Gestation periods (time of development within uterus) varies among species
• Adapted for life on land in water, and in air
• Mammal species make up 95 % of all animals
• At least 18 orders exist

Order Insectivora:

• Includes moles, hedgehogs, & shrews
• Small with high metabolic rate
• Found in North America, Europe, & Asia
• Have long, pointed noses to grub for insects & worms
• Teeth adapted to pick up & pierce prey
• Adapted to live on & under ground, in trees, and in water
• Shrews feed above ground & have claws to help sweep invertebrates into their mouths
• Moles live underground, have reduced eyes & no external ears, and have short limbs to dig tunnels

Mole	Shrew

Order Rodentia:

• Largest mammal order (40% of all species)

• Found everywhere except Antarctica

• Includes squirrels, chipmunks, gophers, rats, mice, & porcupines

• Have two instead of four incisors

• Teeth continue to grow throughout their life

• Feed on hard seeds, twigs, roots, & bark

• Gnawing keeps incisors sharp

• High reproductive capacity

• Guinea pig & capybaras are two rodents found in South America

Chipmunk	Porcupine

Order Lagomorpha:

• includes rabbits, hares, & pikas
• Found worldwide
• Have a double row of upper incisors & two large front teeth backed up by two smaller teeth
• Continuous growing teeth
• Herbivores

Pika	Hare

Order Edentata:

• Includes anteaters, armadillos, & sloths
• Found in North, Central, & South America
• Means "without teeth"
• Only anteaters are completely toothless
• Armadillos & sloths have peg-like teeth without enamel
• Have long sticky tongues & claws on powerful front paws to open ant hills& termite nests
• Sloths are herbivores
• Armadillos eat small reptiles, frogs, mollusks, & dead animals

Armadillo	Sloth

Order Chiroptera:

• Only flying mammals
• Includes bats found everywhere except polar regions
• Front limb is modified into a wing with a skin membrane stretching from the finger bones to the hind limb
• Clawed thumb, extending from top edge of wing, is used for walking, climbing, & grasping
• Most are nocturnal (night active)
• Use echolocation (emission of high frequency sounds that bounce off objects) to navigate and locate food
• Have small eyes & large ears
• Feed mainly on insects
• Tropical bats don't use echolocation, but have large eyes & keen sense of smell to find fruit to feed on & nectar

Order Cetacea:

• Includes whales, dolphins, & porpoises
• Most inhabit oceans, but some dolphins live in freshwater rivers
• Have a fish shaped body
• Forelimbs modified as flippers
• No hind limbs
• Broad, flat tails to propel through water
• Breathe through a blowhole on top of the head
• Divided into two groups --- toothed whales & baleen whales
• Toothed whales:
  1. Includes beaked, sperm, beluga, & killer whales; narwhals; dolphins; porpoises
  2. Have 1 to more than 100 teeth
  3. Prey on fish, squid, seals, & other whales

Narwhal	Beluga	Orca

• Baleen whales:
  1. Lack teeth
  2. Includes blue, grey, right & humpbacked whales
  2. Have baleen or thin plates of fingernail like material that hangs from the roof of the mouth
  3. Baleen strain shrimp & other invertebrates from water as food

Blue Whale	Humpbacked Whale

Order Sirenia:

• Includes manatees & dugongs
• Large herbivores
• Inhabit tropical seas, estuaries, & rivers
• Front limbs modified into flippers
• No hind limbs
• Flattened tail for propulsion

Manatees	Dugongs

Order Carnivora:

• Found worldwide
• Includes cats, dogs, raccoons, bears, hyenas, & otters
• Meat eaters (carnivores) mainly
• Many feed on both plants & animals (omnivores)
• Have long canine teeth & strong jaws
• Clawed toes for seizing & holding prey
• Keen sense of sight & smell
• Long limbs for running fast

Raccoons	Hyena

Order Pinnipedia:

• Aquatic carnivores
• Includes sea lions, seals, & walruses
• Streamlined bodies adapted for swimming
• Steer & propel through water using broad, flattened tail
• Called pinnipeds
• Return to land to feed & give birth
• Spend much of their time in cold water
• Large land carnivores so this helps maintain endothermy
• Can remain under water for 5 minutes to an hour for some species

Order Artiodactyla:

• Known as ungulates or hoofed mammals

• Have an even number of toes

• Includes deer, elk, bison, moose, sheep, cows, caribou, goats, pigs, & camels

• Herbivores

• Have large flat molars for grinding plants

• Found everywhere except Antarctica

• Cloven or split hooves

• Fast runners (used for defense)

• Have storage chamber called rumen in stomach where bacteria break down cellulose

• Stored food called cud is chewed again & then swallowed to go through digestive system a second time

Order Perissodactyla:

• Odd toed ungulates

• Includes horses, zebras, rhinoceroses, & tapir

• Most are native to Africa & Asia

• Tapirs are found in Central & South America

• Have a large, convoluted caecum or blind sac near the small intestine where bacteria digest cellulose

Caribou (even-toed)	Tapir (odd-toed)

Order Proboscidea:

• Have a boneless trunk or proboscis
• Includes the African & Asian elephant
• Wooly mammoth is an extinct member of this order
• Largest terrestrial mammal
• Weigh more than 6 tons
• Feed on plants up to 18 hours a day
• Proboscis used to gather leaves from high branches & to suck water without lowering the head
• Modified incisors called tusks help dig for roots & strip bark
• Jagged molars up to 30 cm long grind plants
• Have the longest gestation period (20 months for females & 22 months for males)
• Females can continue to have calves until they are 70 years old

African Elephant	Asian Elephant

Order Primates:

• Includes 2 main groups --- Prosimians & Anthropoids
• Most are omnivores
• Have teeth suitable for a varied diet
• Prosimians include lemurs, tarsiers, & lorises
• Anthropoids include monkeys, apes, & humans
• Anthropoids have a larger brain
• Show more complex behaviors than other animals
• Highly organized social groups
• Gorilla is the largest primate
• Have 2 forward-facing eyes for depth perception
• Have grasping hands & most with grasping feet
• Some have a grasping tail for life in trees
• Live in a variety of habitats

Lemur	Gorilla