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Mammals. Class Mammalia. Small number of species ~4500 But probably more successful than most animal groups (except insects) at exploiting all available environments. Class Mammalia. Very diverse group not constrained by particular lifestyle (like flight in birds)

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class mammalia
Class Mammalia
  • Small number of species ~4500
  • But probably more successful than most animal groups (except insects) at exploiting all available environments
class mammalia1
Class Mammalia
  • Very diverse group not constrained by particular lifestyle (like flight in birds)
  • Diversity makes it difficult for layperson to identify various mammals as being closely related
class mammalia2
Class Mammalia
  • Descended from therapsid reptiles with mammal-like characteristics
  • Important structural changes from reptiles to mammals
class mammalia3
Class Mammalia
  • Limbs from lateral to ventral
  • Higher center of gravity - less stability
  • Required greater development of cerebellum - muscular coordination center in brain
class mammalia4
Class Mammalia
  • Separation of air and food passageways in head
  • Can breathe with mouth full of food
  • Allows prolonged chewing & some early digestion
subclass theria
Subclass Theria
  • Most mammals belong to Subclass Theria
  • Descended from some common ancestor ~150 million years ago
subclass theria1
Subclass Theria
  • Infraclass Metatheria - marsupials - pouched mammals
  • Infraclass Eutheria - placental mammals
subclass prototheria
Subclass Prototheria
  • Monotremes
  • Small group of egg-laying mammals
  • So different from other groups of mammals
  • Entirely different origin?
all mammals
All mammals
  • Characteristics unique and diagnostic for mammals
  • Hair - greatly reduced in aquatic mammals
  • Mammary glands - milk secreting glands for nourishing young
integument derivatives
Integument & Derivatives
  • Skin generally thicker than in other vertebrates
  • Dermis thicker than epidermis
  • Epidermis very thin where covered with hair, thicker on palms, soles
integument derivatives1
Integument & Derivatives
  • Hair derived from epidermis
  • Probably evolved from reptilian scales
  • Scales still present in some (tail of rat, beaver)
integument derivatives2
Integument & Derivatives
  • Grows from follicle
  • Epidermal structure sunk deep into dermal layer and beyond
  • Grows by addition of new cells at base of follicle
integument derivatives3
Integument & Derivatives
  • Cells pushed upward die from lack of nourishment
  • Dead cells mostly keratin - same material in nails, claws, feathers
integument derivatives4
Integument & Derivatives
  • Hair consists of 3 layers
  • Medulla - core
  • Cortex - contains pigment
  • Cuticle - composed of imbricated scales
  • Different types of hair result from differential development of the 3 layers
integument derivatives5
Integument & Derivatives
  • Each follicle has muscle attached to it - erector muscle
  • Contraction causes hair to stand up straight
  • Increase insulation thickness, serve as warning
fur or pelage
Fur or Pelage
  • Most mammals have two kinds of hair
  • Thick, soft underhair - provides insulation
  • Coarse, long guard hair - protects and provides coloration
fur or pelage1
Fur or Pelage
  • Hair stops growing when it reaches certain length
  • Remains in follicle until new growth starts, then falls out
fur or pelage2
Fur or Pelage
  • Mammals lose hair in periodic molts
  • Most have 2 annual molts - entire pelage shed (humans shed and replace continually)
  • Spring - thin summer
  • Fall - heavy winter
fur or pelage3
Fur or Pelage
  • Pigmentation and molts allow mammals to be different colors in different seasons
  • Brown in summer
  • White in winter - leukemism
fur or pelage4
Fur or Pelage
  • Lack of pigment results in albinism - recessive gene - blocks pigment formation (don’t confuse with leukemism)
  • Excess of black pigment is melanism
derivatives of hair
Derivatives of Hair
  • Vibrissae - sensory hairs on snouts, other parts of head
  • Incorrectly called whiskers
derivatives of hair1
Derivatives of Hair
  • Quills - defensive structures in porcupines, hedgehogs, echidnas
  • Break off after barbed tip embeds in flesh of other animal
  • Work in deeper with time
  • Mammals also have variety of epidermal glands
  • Greatest variety among vertebrates
  • 4 basic types
  • Sweat glands - simple, tubular, highly coiled
  • Cover most of body
  • Not found in other vertebrates
  • Open directly to skin surface
  • Two types
  • Sweat glands - eccrine glands
  • Secrete watery sweat for temperature regulation
  • Hairless regions in most mammals (especially foot pads)
  • Some mammals don’t have eccrine glands - rodents, rabbits, whales
  • Some have them all over body - humans, horses, dogs
  • Racial differences in abundance in humans
  • Sweat glands - apocrine glands
  • Found in all mammals
  • Longer, more winding than eccrine glands
  • Open into follicle at surface
  • Secretion not involved with heat regulation
  • Apocrine gland activity correlated with some aspects of sexual cycles
  • Human females have twice as many as males
  • Scent glands - location and function vary
  • Communication, warning, defense, attraction
  • E.g., skunk
  • Humans have many, but taught to dislike their scent
  • Sebaceous glands - associated with hair follicle
  • Secrete fat (sebum) to keep hair and skin soft
  • Polite fat - does not turn rancid
  • Generally all over body - most numerous on human scalp, face
  • Mammary glands - modification of apocrine, sebaceous glands?
  • Present in both genders, functional only in female
  • Secrete milk to nourish young
  • Contain varying quantities of fat (3-5%), protein, carbohydrate, salts
  • Higher fat content (30-40%) in marine and arctic mammals, where development is rapid
horns antlers
Horns & Antlers
  • 3 kinds of horns or horn-like structures found in mammals
  • 1) true horns
  • 2) antlers
  • 3) rhino horns
horns antlers1
Horns & Antlers
  • True horns
  • Found in ruminants like cows, goats, antelope
  • Hollow sheaths of keratinized epidermis surrounding core of bone arising from skull
horns antlers2
Horns & Antlers
  • Not normally shed
  • Not branched (but may be greatly curved, twisted)
  • Found in both sexes
horns antlers3
Horns & Antlers
  • Antlers
  • Deer family (Cervidae)
  • Generally males only (except caribou - female’s smaller)
  • Entirely bone when mature
horns antlers4
Horns & Antlers
  • Annual growth
  • Develop beneath cover of highly vascularized soft skin - velvet
  • Growth complete, blood vessels constrict, velvet dies and is rubbed off
horns antlers5
Horns & Antlers
  • Antlers dropped after breeding season
  • New buds appear within few months
  • New pair larger, more elaborate
  • Strain on mineral metabolism - moose, elk must accumulate 50+ lbs of calcium salts from vegetable diet
horns antlers6
Horns & Antlers
  • Rhinoceros horn
  • Hairlike horny fibers arise from dermal papillae
  • Cemented together to form single horn
  • Dagger handles and medicinal uses
  • Teeth are a less obvious characteristic of mammals
  • Reveal more about lifestyle than any other characteristic
  • Not in monotremes, some whales, anteaters
  • Diphyodont teeth - two sets of teeth
  • Set of deciduous “milk teeth” replaced by set of permanent teeth
  • Reptiles have polyphyodont teeth - many sets - all are homodont - uniform, unspecialized
  • Mammals have heterodont teeth - specialized for various functions
  • Incisors - snip, bite - simple crowns, slightly sharp edges
  • Canines - piercing - pointed, long conical crowns
  • Premolars - shear, slice - flat compressed crowns with 1 or 2 cusps
  • Molars - crushing, grinding - broad with variable cusp arrangement
  • Always belong to the permanent set
  • Different diets necessitate differing development of different teeth
  • Carnivores - large canines, some small and/or modified molars and premolars
  • Rodents and herbivores - large incisors, reduced canines, large molars
  • Incisors grow continually, must be worn away to keep pace with growth
digestive systems
Digestive Systems
  • Different diets also necessitate differing digestive systems
  • Herbivores face special problem - indigestibility of cellulose, chief carbohydrate in plants
digestive systems1
Digestive Systems
  • No digestive enzyme to break down cellulose
  • Depend on anaerobic bacteria to do it
  • Developed various digestive structures where microbes can do their thing
digestive systems2
Digestive Systems
  • Two basic approaches
  • 1) hind-gut approach
  • 2) fore-gut approach
digestive systems3
Digestive Systems
  • Hind-gut approach
  • Horses and rabbits and others
  • Large sidepocket - cecum - at junction of small, large intestines
  • Houses microbes
digestive systems4
Digestive Systems
  • Sometimes all isn’t digested first time through
  • Rabbits, hares, some rodents eat fecal pellets - coprophagy
  • More bacterial fermentation, chance to absorb vitamins manufactured by bacteria
digestive systems5
Digestive Systems
  • Humans have vestigial cecum - appendix
digestive systems6
Digestive Systems
  • Fore-gut approach
  • Cattle, deer, sheep, antelope are ruminants
  • Have huge, 4-chambered stomach where digestion occurs
digestive systems7
Digestive Systems
  • Grass passed down esophagus to rumen
  • Broken down by bacteria and formed into small balls of cud in reticulum
  • Regurgitated to mouth and chewed to crush fibers
digestive systems8
Digestive Systems
  • Swallowed to rumen again for further digestion by bacteria
  • Finally passed through reticulum and churned in omasum
digestive systems9
Digestive Systems
  • Passed into abomasum - true stomach
  • Proteolytic enzymes secreted, normal digestion occurs
digestive systems10
Digestive Systems
  • Small intestine very long, coiled
  • Much longer in herbivores than in carnivores, insectivores
  • Cow small intestine - 50+ m (165 feet)
size vs food consumption
Size vs. Food Consumption
  • The smaller the mammal, the greater its metabolic rate, and the more it must eat relative to its size
  • Small mammals spend more time hunting, eating than large mammals
size vs food consumption1
Size vs. Food Consumption
  • 2 g shrew eats > its body weight in food each day
  • Will starve to death in few hours if deprived of food
size vs food consumption2
Size vs. Food Consumption
  • Large carnivore may only need one meal every few days to remain healthy
  • Few mammals make seasonal migrations
  • Much more difficult than for birds
  • Most that do live in, near North America
  • Barren-ground caribou - seasonal movements >1000 km
  • North for calving, south for winter
  • Longest mammal migrants are whales, seals
  • Fur seal females migrate 2800 km to give birth, winter
  • Males stay north
  • Few bats with power of flight use it to migrate
  • Most hibernate during winter
  • 4 spp. of American bats migrate - red bat
  • Winter in Mexico, summer north, west
  • Flight, gliding evolved independently in several different groups: marsupials, rodents, lemurs, bats
  • Bats are only true fliers - nocturnal insectivore niche left open by most birds
  • Success of bats:
  • 1) flight
  • 2) ability to navigate via echolocation
  • Fly and avoid obstacles in complete darkness
  • Locate & catch insects with precision and speed
  • Find way deep into caves - new habitat
  • Emit short pulses (5-10 msec) from mouth
  • Ultrasonic to human ear
  • 10-200 pulses/sec
  • Echo received with great ears - form image of surroundings as good as eyes of other mammals
  • May be used by other insectivorous mammals: shrews, tenrecs
  • Crudely developed compared to bats
  • Echolocation highly developed in toothed whales, e.g., sperm whale
  • Varying frequency clicks produced in sinus passages
  • Focused by lens-shaped melon in forehead
  • Returning echoes channeled through oil-filled cavity in lower jaw to inner ear
  • Allows whales to determine size, shape, speed, distance, directions, density of everything in water
  • Keep track of members of pod
  • True hibernators: ground squirrels, woodchucks
  • Body temperature falls within few degrees of freezing
  • Breathing, heart rates drop extremely low
  • Not true hibernation: bears
  • Breathing, heart rates fall, but body temperature remains similar
  • Most mammals have definite mating seasons
  • Usually winter or spring
  • Timed to coincide with most favorable time for rearing young after birth
  • Female mating function restricted to time during periodic cycle - estrous cycle
  • Female receptive during brief period of cycle - estrus or heat
  • Several other stages
  • Proestrus - period of preparation
  • New ovarian follicles grow
  • Estrus - mating, ovulation, fertilization, implantation, pregnancy
  • Metestrus - if no mating or fertilization, a period of repair
  • Diestrus - uterus becomes small, anemic
  • Monestrous - single estrus during breeding season
  • Dogs, foxes, bats
  • Polyestrous - recurrence of estrus during breeding season
  • Mice squirrels, tropical animals
  • Humans and Old World monkeys have slightly different cycle
  • Post-ovulation period terminated by menstration - menstrual cycle
  • 3 different patterns of reproduction among mammals
  • 1) monotremes
  • 2) marsupials
  • 3) placentals
  • Monotremes - egg-laying mammals
  • One breeding season each year
  • Ovulated eggs (2) fertilized in oviduct
  • Shell added in oviduct
  • Eggs laid in burrow nest
  • Incubated for 12 days
  • Hatch, fed milk (licking, not suckling)
  • No gestation - period of pregnancy
  • Developing embryo uses nutrients in egg
  • Young reared on milk
  • Marsupials - pouched mammals
  • Brief gestation period, but physiology and lactation complicated
  • E.g., red kangaroo
  • 1st pregnancy of season followed by 33-day gestation, joey born underdeveloped
  • Crawls into pouch, attaches to nipple
  • Mother immediately becomes pregnant again
  • Presence of young in pouch arrests development at 100-cell stage - diapause
  • Lasts ~235 days until joey leaves pouch
  • 2nd joey develops, born in ~month, enters pouch
  • Becomes pregnant again
  • Arrested development
  • Oldest joey returns to nurse from time to time
  • 3 young at once
  • Some marsupial variations
    • Development delays
  • Common features
    • Born at underdeveloped stage
    • Prolonged development attached to mammary gland
  • Placentals - most successful mammals
  • Reproductive investment is in gestation
  • Embryo nourished by food via placenta
  • Gestation variable
  • Mice - 21 days
  • Rabbits - 30-36 days
  • Cats, dogs - 60 days
  • Cattle - 280 days
  • Elephants - 22 months
  • Baleen whales - 12 months
  • Bats - 4-5 months
  • Variable condition at birth - well-furred and mobile to naked, blind, helpless
  • Human growth slower than any other mammal
of young
# of Young
  • Smaller animals, larger litters
  • Larger animals, smaller litters
  • Status in food web important
  • Carnivores - 1 litter of 3-5 young
  • Mice - 17 litters of 4-9 young per year
of young1
# of Young
  • Large mammals - single young with each pregnancy
  • Elephant - 4 young per 50-year reproductive life
  • Defended area for exclusive use
  • Marked using scent glands
  • Varies in size from huge (grizzly bear) to small (squirrel)
  • Owner comfortable within territory, intruder at “psychological” disadvantage
  • Owner comfortable within territory, intruder at “psychological” disadvantage
  • Some territories established for use by family unit
  • Male beaver defends territory, female and young use it
  • Some live in friendly towns - prairie dog
  • Parents give old home to young and move out
home range
Home Range
  • Larger foraging area surrounding defended territory
  • Neutral zone used for foraging by owners of several territories
us them
Us & Them
  • Biggest impact - domestication
  • Dogs, cats 10,000 years ago
  • Food animals much later
us them1
Us & Them
  • Beasts of burden
  • Some no longer exist in wild - llama, alpaca, 1-humped Arabian camel
us them2
Us & Them
  • Some not truly domesticated - do not breed in captivity
  • Reindeer, Asian elephant
us them3
Us & Them
  • Problem mammals - rodents, rabbits
  • Damage crops, foods, carry diseases
us them4
Us & Them
  • Problems with us
  • 300 species endangered
  • Includes all cetaceans, cats, otters, primates
  • Hunting, collecting, habitat destruction, species introductions