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)
Diversity makes it
difficult for layperson
to identify various
mammals as being
closely related
Class Mammalia


Descended from
therapsid reptiles with
mammal-like
characteristics
Important structural
changes from reptiles
to mammals
Class Mammalia



Limbs from lateral to
ventral
Higher center of
gravity - less stability
Required greater
development of
cerebellum - muscular
coordination center in
brain
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


Most mammals
belong to Subclass
Theria
Descended from
some common
ancestor ~150 million
years ago
Subclass Theria


Infraclass Metatheria
- marsupials pouched mammals
Infraclass Eutheria placental mammals
Subclass Prototheria




Monotremes
Small group of egglaying mammals
So different from
other groups of
mammals
Entirely different
origin?
All mammals



Characteristics
unique and diagnostic
for mammals
Hair - greatly reduced
in aquatic mammals
Mammary glands milk secreting glands
for nourishing young
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 & Derivatives



Hair derived from
epidermis
Probably evolved
from reptilian scales
Scales still present in
some (tail of rat,
beaver)
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 & Derivatives


Cells pushed upward
die from lack of
nourishment
Dead cells mostly
keratin - same
material in nails,
claws, feathers
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 & 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



Most mammals have
two kinds of hair
Thick, soft underhair provides insulation
Coarse, long guard
hair - protects and
provides coloration
Fur or Pelage


Hair stops growing
when it reaches
certain length
Remains in follicle
until new growth
starts, then falls out
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 Pelage



Pigmentation and
molts allow mammals
to be different colors
in different seasons
Brown in summer
White in winter leukemism
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


Vibrissae - sensory
hairs on snouts, other
parts of head
Incorrectly called
whiskers
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
Glands



Mammals also have
variety of epidermal
glands
Greatest variety
among vertebrates
4 basic types
Glands





Sweat glands simple, tubular, highly
coiled
Cover most of body
Not found in other
vertebrates
Open directly to skin
surface
Two types
Glands



Sweat glands eccrine glands
Secrete watery sweat
for temperature
regulation
Hairless regions in
most mammals
(especially foot pads)
Glands



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





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


Apocrine gland
activity correlated with
some aspects of
sexual cycles
Human females have
twice as many as
males
Glands




Scent glands location and function
vary
Communication,
warning, defense,
attraction
E.g., skunk
Humans have many,
but taught to dislike
their scent
Glands




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



Mammary glands modification of
apocrine, sebaceous
glands?
Present in both
genders, functional
only in female
Secrete milk to
nourish young
Glands


Contain varying
quantities of fat (35%), protein,
carbohydrate, salts
Higher fat content
(30-40%) in marine
and arctic mammals,
where development is
rapid
Horns & Antlers




3 kinds of horns or
horn-like structures
found in mammals
1) true horns
2) antlers
3) rhino horns
Horns & Antlers



True horns
Found in ruminants
like cows, goats,
antelope
Hollow sheaths of
keratinized epidermis
surrounding core of
bone arising from
skull
Horns & Antlers



Not normally shed
Not branched (but
may be greatly
curved, twisted)
Found in both sexes
Horns & Antlers




Antlers
Deer family
(Cervidae)
Generally males only
(except caribou female’s smaller)
Entirely bone when
mature
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 & 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 & Antlers




Rhinoceros horn
Hairlike horny fibers
arise from dermal
papillae
Cemented together to
form single horn
Dagger handles and
medicinal uses
Teeth



Teeth are a less obvious characteristic of
mammals
Reveal more about lifestyle than any other
characteristic
Not in monotremes, some whales, anteaters
Teeth



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

Mammals have heterodont teeth - specialized
for various functions
Teeth
Teeth

Incisors - snip, bite - simple crowns, slightly
sharp edges
Teeth

Canines - piercing - pointed, long conical crowns
Teeth

Premolars - shear, slice - flat compressed
crowns with 1 or 2 cusps
Teeth


Molars - crushing, grinding - broad with variable
cusp arrangement
Always belong to the permanent set
Teeth


Different diets
necessitate differing
development of
different teeth
Carnivores - large
canines, some small
and/or modified
molars and premolars
Teeth


Rodents and
herbivores - large
incisors, reduced
canines, large molars
Incisors grow
continually, must be
worn away to keep
pace with growth
Teeth
Digestive Systems


Different diets also
necessitate differing
digestive systems
Herbivores face
special problem indigestibility of
cellulose, chief
carbohydrate in plants
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 Systems



Two basic
approaches
1) hind-gut approach
2) fore-gut approach
Digestive Systems




Hind-gut approach
Horses and rabbits
and others
Large sidepocket cecum - at junction of
small, large intestines
Houses microbes
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 Systems

Humans have
vestigial cecum appendix
Digestive Systems



Fore-gut approach
Cattle, deer, sheep,
antelope are
ruminants
Have huge, 4chambered stomach
where digestion
occurs
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 Systems


Swallowed to rumen
again for further
digestion by bacteria
Finally passed
through reticulum and
churned in omasum
Digestive Systems


Passed into
abomasum - true
stomach
Proteolytic enzymes
secreted, normal
digestion occurs
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


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


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

Large carnivore may
only need one meal
every few days to
remain healthy
Migration



Few mammals make
seasonal migrations
Much more difficult
than for birds
Most that do live in,
near North America
Migration


Barren-ground
caribou - seasonal
movements >1000
km
North for calving,
south for winter
Migration



Longest mammal
migrants are whales,
seals
Fur seal females
migrate 2800 km to
give birth, winter
Males stay north
Migration




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


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



Success of bats:
1) flight
2) ability to navigate
via echolocation
Echolocation



Fly and avoid
obstacles in complete
darkness
Locate & catch
insects with precision
and speed
Find way deep into
caves - new habitat
Echolocation




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


May be used by other
insectivorous
mammals: shrews,
tenrecs
Crudely developed
compared to bats
Echolocation


Echolocation highly
developed in toothed
whales, e.g., sperm
whale
Varying frequency
clicks produced in
sinus passages
Echolocation


Focused by lensshaped melon in
forehead
Returning echoes
channeled through
oil-filled cavity in
lower jaw to inner ear
Echolocation


Allows whales to
determine size,
shape, speed,
distance, directions,
density of everything
in water
Keep track of
members of pod
Hibernation



True hibernators:
ground squirrels,
woodchucks
Body temperature
falls within few
degrees of freezing
Breathing, heart rates
drop extremely low
Hibernation


Not true hibernation:
bears
Breathing, heart rates
fall, but body
temperature remains
similar
Reproduction



Most mammals have
definite mating
seasons
Usually winter or
spring
Timed to coincide with
most favorable time
for rearing young after
birth
Reproduction



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


Proestrus - period of
preparation
New ovarian follicles
grow
Reproduction

Estrus - mating,
ovulation, fertilization,
implantation,
pregnancy
Reproduction

Metestrus - if no
mating or fertilization,
a period of repair
Reproduction

Diestrus - uterus
becomes small,
anemic
Reproduction




Monestrous - single
estrus during breeding
season
Dogs, foxes, bats
Polyestrous recurrence of estrus
during breeding season
Mice squirrels, tropical
animals
Reproduction


Humans and Old
World monkeys have
slightly different cycle
Post-ovulation period
terminated by
menstration menstrual cycle
Reproduction




3 different patterns of
reproduction among
mammals
1) monotremes
2) marsupials
3) placentals
Reproduction






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




Hatch, fed milk (licking,
not suckling)
No gestation - period of
pregnancy
Developing embryo
uses nutrients in egg
Young reared on milk
Reproduction



Marsupials - pouched
mammals
Brief gestation period,
but physiology and
lactation complicated
E.g., red kangaroo
Reproduction



1st pregnancy of
season followed by
33-day gestation, joey
born underdeveloped
Crawls into pouch,
attaches to nipple
Mother immediately
becomes pregnant
again
Reproduction



Presence of young in
pouch arrests
development at 100cell stage - diapause
Lasts ~235 days until
joey leaves pouch
2nd joey develops,
born in ~month,
enters pouch
Reproduction




Becomes pregnant
again
Arrested development
Oldest joey returns to
nurse from time to
time
3 young at once
Reproduction

Some marsupial
variations


Development delays
Common features
 Born at
underdeveloped
stage
 Prolonged
development
attached to
mammary gland
Reproduction



Placentals - most
successful
mammals
Reproductive
investment is in
gestation
Embryo nourished
by food via placenta
Reproduction








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


Variable condition at
birth - well-furred
and mobile to
naked, blind,
helpless
Human growth
slower than any
other mammal
# 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 Young


Large mammals single young with
each pregnancy
Elephant - 4 young
per 50-year
reproductive life
Territory



Defended area for
exclusive use
Marked using scent
glands
Varies in size from
huge (grizzly bear)
to small (squirrel)
Territory

Owner comfortable
within territory,
intruder at
“psychological”
disadvantage
Territory

Owner comfortable
within territory,
intruder at
“psychological”
disadvantage
Territory


Some territories
established for use
by family unit
Male beaver
defends territory,
female and young
use it
Territory


Some live in friendly
towns - prairie dog
Parents give old
home to young and
move out
Home Range


Larger foraging area
surrounding
defended territory
Neutral zone used
for foraging by
owners of several
territories
Us & Them



Biggest impact domestication
Dogs, cats 10,000
years ago
Food animals much
later
Us & Them


Beasts of burden
Some no longer
exist in wild - llama,
alpaca, 1-humped
Arabian camel
Us & Them


Some not truly
domesticated - do
not breed in captivity
Reindeer, Asian
elephant
Us & Them


Problem mammals rodents, rabbits
Damage crops,
foods, carry
diseases
Us & Them




Problems with us
300 species
endangered
Includes all cetaceans,
cats, otters, primates
Hunting, collecting,
habitat destruction,
species introductions