Mammals Class Mammalia n n Small number of

Mammals

Class Mammalia n n Small number of species ~4500 But probably more successful than most animal groups (except insects) at exploiting all available environments

Class Mammalia n n 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 Mammalia n n Descended from therapsid reptiles with mammal-like characteristics Important structural changes from reptiles to mammals

Class Mammalia n n n Limbs from lateral to ventral Higher center of gravity - less stability Required greater development of cerebellum - muscular coordination center in brain

Class Mammalia n n n Separation of air and food passageways in head Can breathe with mouth full of food Allows prolonged chewing & some early digestion

Subclass Theria n n Most mammals belong to Subclass Theria Descended from some common ancestor ~150 million years ago

Subclass Theria n n Infraclass Metatheria marsupials - pouched mammals Infraclass Eutheria placental mammals

Subclass Prototheria n n Monotremes Small group of egglaying mammals So different from other groups of mammals Entirely different origin?

All mammals n n n Characteristics unique and diagnostic for mammals Hair - greatly reduced in aquatic mammals Mammary glands milk secreting glands for nourishing young

Integument & Derivatives n n n Skin generally thicker than in other vertebrates Dermis thicker than epidermis Epidermis very thin where covered with hair, thicker on palms, soles

Integument & Derivatives n n n Hair derived from epidermis Probably evolved from reptilian scales Scales still present in some (tail of rat, beaver)

Integument & Derivatives n n n Grows from follicle Epidermal structure sunk deep into dermal layer and beyond Grows by addition of new cells at base of follicle

Integument & Derivatives n n Cells pushed upward die from lack of nourishment Dead cells mostly keratin - same material in nails, claws, feathers

Integument & Derivatives n n n 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 & Derivatives n n n 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 n n n Most mammals have two kinds of hair Thick, soft underhair provides insulation Coarse, long guard hair - protects and provides coloration

Fur or Pelage n n Hair stops growing when it reaches certain length Remains in follicle until new growth starts, then falls out

Fur or Pelage n n 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 Pelage n n n Pigmentation and molts allow mammals to be different colors in different seasons Brown in summer White in winter leukemism

Fur or Pelage n n 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 n n Vibrissae - sensory hairs on snouts, other parts of head Incorrectly called whiskers

Derivatives of Hair n n n Quills - defensive structures in porcupines, hedgehogs, echidnas Break off after barbed tip embeds in flesh of other animal Work in deeper with time

Glands n n n Mammals also have variety of epidermal glands Greatest variety among vertebrates 4 basic types

Glands n n n Sweat glands simple, tubular, highly coiled Cover most of body Not found in other vertebrates Open directly to skin surface Two types

Glands n n n Sweat glands eccrine glands Secrete watery sweat for temperature regulation Hairless regions in most mammals (especially foot pads)

Glands n n n 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

Glands n n n 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

Glands n n Apocrine gland activity correlated with some aspects of sexual cycles Human females have twice as many as males

Glands n n Scent glands location and function vary Communication, warning, defense, attraction E. g. , skunk Humans have many, but taught to dislike their scent

Glands n n 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

Glands n n n Mammary glands modification of apocrine, sebaceous glands? Present in both genders, functional only in female Secrete milk to nourish young

Glands n n Contain varying quantities of fat (35%), protein, carbohydrate, salts Higher fat content (3040%) in marine and arctic mammals, where development is rapid

Horns & Antlers n n 3 kinds of horns or horn-like structures found in mammals 1) true horns 2) antlers 3) rhino horns

Horns & Antlers n n n True horns Found in ruminants like cows, goats, antelope Hollow sheaths of keratinized epidermis surrounding core of bone arising from skull

Horns & Antlers n n n Not normally shed Not branched (but may be greatly curved, twisted) Found in both sexes

Horns & Antlers n n Antlers Deer family (Cervidae) Generally males only (except caribou female’s smaller) Entirely bone when mature

Horns & Antlers n n n Annual growth Develop beneath cover of highly vascularized soft skin - velvet Growth complete, blood vessels constrict, velvet dies and is rubbed off

Horns & Antlers n n 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 & Antlers n n Rhinoceros horn Hairlike horny fibers arise from dermal papillae Cemented together to form single horn Dagger handles and medicinal uses

Teeth n n n Teeth are a less obvious characteristic of mammals Reveal more about lifestyle than any other characteristic Not in monotremes, some whales, anteaters

Teeth n n n 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

Teeth n Mammals have heterodont teeth - specialized for various functions

Teeth

Teeth n Incisors - snip, bite - simple crowns, slightly sharp edges

Teeth n Canines - piercing - pointed, long conical crowns

Teeth n Premolars - shear, slice - flat compressed crowns with 1 or 2 cusps

Teeth n n Molars - crushing, grinding - broad with variable cusp arrangement Always belong to the permanent set

Teeth n n Different diets necessitate differing development of different teeth Carnivores - large canines, some small and/or modified molars and premolars

Teeth n n Rodents and herbivores - large incisors, reduced canines, large molars Incisors grow continually, must be worn away to keep pace with growth

Teeth

Digestive Systems n n Different diets also necessitate differing digestive systems Herbivores face special problem indigestibility of cellulose, chief carbohydrate in plants

Digestive Systems n n n 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 Systems n n n Two basic approaches 1) hind-gut approach 2) fore-gut approach

Digestive Systems n n Hind-gut approach Horses and rabbits and others Large sidepocket cecum - at junction of small, large intestines Houses microbes

Digestive Systems n n n 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 Systems n Humans have vestigial cecum appendix

Digestive Systems n n n Fore-gut approach Cattle, deer, sheep, antelope are ruminants Have huge, 4 chambered stomach where digestion occurs

Digestive Systems n n n 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 Systems n n Swallowed to rumen again for further digestion by bacteria Finally passed through reticulum and churned in omasum

Digestive Systems n n Passed into abomasum - true stomach Proteolytic enzymes secreted, normal digestion occurs

Digestive Systems n n n Small intestine very long, coiled Much longer in herbivores than in carnivores, insectivores Cow small intestine 50+ m (165 feet)

Size vs. Food Consumption n n 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 Consumption n n 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 Consumption n Large carnivore may only need one meal every few days to remain healthy

Migration n Few mammals make seasonal migrations Much more difficult than for birds Most that do live in, near North America

Migration n n Barren-ground caribou - seasonal movements >1000 km North for calving, south for winter

Migration n Longest mammal migrants are whales, seals Fur seal females migrate 2800 km to give birth, winter Males stay north

Migration n n 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 n n 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

Flight n n n Success of bats: 1) flight 2) ability to navigate via echolocation

Echolocation n Fly and avoid obstacles in complete darkness Locate & catch insects with precision and speed Find way deep into caves - new habitat

Echolocation n n 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

Echolocation n n May be used by other insectivorous mammals: shrews, tenrecs Crudely developed compared to bats

Echolocation n n Echolocation highly developed in toothed whales, e. g. , sperm whale Varying frequency clicks produced in sinus passages

Echolocation n n Focused by lensshaped melon in forehead Returning echoes channeled through oilfilled cavity in lower jaw to inner ear

Echolocation n n Allows whales to determine size, shape, speed, distance, directions, density of everything in water Keep track of members of pod

Hibernation n True hibernators: ground squirrels, woodchucks Body temperature falls within few degrees of freezing Breathing, heart rates drop extremely low

Hibernation n n Not true hibernation: bears Breathing, heart rates fall, but body temperature remains similar

Reproduction n Most mammals have definite mating seasons Usually winter or spring Timed to coincide with most favorable time for rearing young after birth

Reproduction n Female mating function restricted to time during periodic cycle - estrous cycle Female receptive during brief period of cycle - estrus or heat Several other stages

Reproduction n n Proestrus - period of preparation New ovarian follicles grow

Reproduction n Estrus - mating, ovulation, fertilization, implantation, pregnancy

Reproduction n Metestrus - if no mating or fertilization, a period of repair

Reproduction n Diestrus - uterus becomes small, anemic

Reproduction n n Monestrous - single estrus during breeding season Dogs, foxes, bats Polyestrous recurrence of estrus during breeding season Mice squirrels, tropical animals

Reproduction n n Humans and Old World monkeys have slightly different cycle Post-ovulation period terminated by menstration menstrual cycle

Reproduction n n 3 different patterns of reproduction among mammals 1) monotremes 2) marsupials 3) placentals

Reproduction n n n Monotremes - egglaying 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

Reproduction n n Hatch, fed milk (licking, not suckling) No gestation - period of pregnancy Developing embryo uses nutrients in egg Young reared on milk

Reproduction n Marsupials - pouched mammals Brief gestation period, but physiology and lactation complicated E. g. , red kangaroo

Reproduction n 1 st pregnancy of season followed by 33 -day gestation, joey born underdeveloped Crawls into pouch, attaches to nipple Mother immediately becomes pregnant again

Reproduction n Presence of young in pouch arrests development at 100 cell stage - diapause Lasts ~235 days until joey leaves pouch 2 nd joey develops, born in ~month, enters pouch

Reproduction n n Becomes pregnant again Arrested development Oldest joey returns to nurse from time to time 3 young at once

Reproduction n Some marsupial variations n n Development delays Common features n Born at underdeveloped stage n Prolonged development attached to mammary gland

Reproduction n Placentals - most successful mammals Reproductive investment is in gestation Embryo nourished by food via placenta

Reproduction n n n n 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

Reproduction n n Variable condition at birth - well-furred and mobile to naked, blind, helpless Human growth slower than any other mammal

# of Young n n n Smaller animals, larger litters Larger animals, smaller litters Status in food web important Carnivores - 1 litter of 35 young Mice - 17 litters of 4 -9 young per year

# of Young n n Large mammals single young with each pregnancy Elephant - 4 young per 50 -year reproductive life

Territory n n n Defended area for exclusive use Marked using scent glands Varies in size from huge (grizzly bear) to small (squirrel)

Territory n Owner comfortable within territory, intruder at “psychological” disadvantage

Territory n Owner comfortable within territory, intruder at “psychological” disadvantage

Territory n n Some territories established for use by family unit Male beaver defends territory, female and young use it

Territory n n Some live in friendly towns - prairie dog Parents give old home to young and move out

Home Range n n Larger foraging area surrounding defended territory Neutral zone used foraging by owners of several territories

Us & Them n n n Biggest impact domestication Dogs, cats 10, 000 years ago Food animals much later

Us & Them n n Beasts of burden Some no longer exist in wild - llama, alpaca, 1 -humped Arabian camel

Us & Them n n Some not truly domesticated - do not breed in captivity Reindeer, Asian elephant

Us & Them n n Problem mammals rodents, rabbits Damage crops, foods, carry diseases

Us & Them n n Problems with us 300 species endangered Includes all cetaceans, cats, otters, primates Hunting, collecting, habitat destruction, species introductions