Mammal - BIOLOGY JUNCTION

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

Lycaenops: drawing by Steve Kirk - Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals, ed.. Barry Cox

TherapsidEarly 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

Section 1 Review

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

photograph of kangaroo and her joey
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

Section 2 Review

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