Mammals
Chapter 28
I. Diversity
Only 4600 living species but most highly
differentiated of all animal groups
Many domesticated to use as food,
clothing, pets, beasts of burden, and in
research
Habitat destruction is the cause of 300
species and subspecies being listed as
endangered
II. Origin
A. Synapsids
 First amniotes to radiate
into fully terrestrial
habitats
 Pair of openings in skull
roof
 Over 150 million years
small, hairless
ectothermic ancestors
evolved into today’s furry
endotherms
 Herbivorous and
carnivorous pelycosaurs
B. Therapsids
 Arose from carnivorous
synapsid lineage
 Only synapsid group to
survive beyond
Paleozoic
 Efficient erect gait with
limbs beneath body
 Cerebellum expanded to
coordinate more muscles
 Most died out in Permian
extinction
C. Cynodonts
Therapsid subgroup that survived into
Mesozoic
Higher metabolic rate to support more
active lifestyle
Skeletal changes improved flexibility,
agility, and muscle attachment
Developed secondary palate that
allowed animal to breathe while eating
prey; important innovation that allowed
later mammals to breathe while suckling
D. Diphyodonts
 Early mammals evolved in Triassic, small and shrewlike
and nocturnal
 Diphyodonts means teeth replaced once with permanent
teeth
 Endothermic but cooler than placental mammals
 Hair with sebaceous and sweat glands
 Hatched from eggs and relied on mammary milk
 Radiated in Eocene after extinction of many amniote
groups at end of Cretaceous
III. General Characteristics
 Hair; even in aquatic
forms may be few but
present
 Mammary glands to
nourish young
 Most specialized
placenta to feed
embryo
 More advanced
nervous system
IV. Skin
 Thick
 Dermis much thicker than epidermis
 Thin epidermis protected by hair
V. Hair
A. Structure
 Hair follicle sunk in
dermis of skin
 Cells divide in follicle; as
they grow away from
source of nourishment,
they die, forming hair
shaft
 Made of protein keratin
 Three layers: pith center
surrounded by cortex of
pigment, then outer
cuticle made of scales
B. Function
Protection against wear or attack (quills)
Concealment—spots , stripes, salt-andpepper disrupt coloration
Waterproofing
Buoyancy
Signaling & sensing--coarse long guard
hairs and whiskers
Thermal insulation--dense soft underhair
Hair
C. Molting
 Usually twice in spring
and fall
 Some have winter
coat which is heavier
and may be white for
camouflage;
condition called
leukemism which
also includes dark
eyes, dark ear tips,
noses , etc
VI. Horns & Antlers
 Found in ruminants such
as sheep and cattle
 Hollow sheaths of
epidermis surrounding a
core of bone from skull
 Not shed or branched,
but may be greatly
curved
 Found in both sexes and
grow continuously
A. Horns
B. Antlers
 Deer family, males only
 When, mature composed
of solid bone
 Covered in spring by
highly vascular skin
called “velvet’
 Before breeding velvet
drops off; after breeding
antlers drop off
 New set bigger than last
VII. Glands
A. Sweat
 1. Eccrine
 Watery fluid
evaporates heat from
surface of skin
 Found in hairless
areas
 Absent in rodents,
rabbits, and whales
2. Apocrine
Larger than eccrine and open onto hair
follicle
Forms film on skin
Related to reproductive cycle
In humans, develop at puberty in armpits,
groin, ear canals
B. Scent
 Found in all mammals
though vary in location
 Used for communication,
warning, defense, and
marking territory
 Stronger during breeding
season to attract mates
 Skunks, minks, and
weasels have very strong
glands near anus
C. Sebaceous
 Associated with hair
follicles but some
open directly onto
skin; all over body
 Fats and oils that
keep skin soft, and
hair flexible and
glossy
D. Mammary
 Modified apocrine glands
 Rudimentary in males; occur on all females
 Swelling when pregnant or nursing
Humans,
develop at
puberty with
fat; further
development
at pregnancy
VIII. Teeth
A. General
Heterodont (diphodont) dentition—
differentiation of teeth for cutting, seizing,
gnawing etc
 Structure reveals life habits of animals;
some are specialists and others
generalists
Primitive mammal arrangement—3
incisors, 1 canine, 4 premolars, 3 molars
1 baby set and 1 adult set of teeth;
generally molars only appear in adult set
Primary Teeth
B. Types
Incisors—sharp edges for snipping, biting
Canines—piercing
Premolars—compressed crowns with 1-2
cusps for shearing, slicing
Molars—large bodies, variable cusp
arrangements for crushing, grinding
IX. Feeding Specializations
A. Insectivores
Shrews, moles, anteaters, bats
Short digestive tract because eat few
plants
Other mammals may eat insects but not
exclusively
B. Herbivores
 Browsers, grazers-- horses, deer, antelope, cattle, sheep,
goats, camelids; Gnawers– rabbits, rodents
 Reduced or absent canines; molars broad and high
crowned
 Rodents have chisel-shaped incisors that growth
throughout life
 Long digestive tracts; ceca add additional absorptive
area
 Fermentation chambers in stomach to aid in digestion of
cellulose
 Ruminants 4-chambered stomachs; food regurgitated and
passed back through
 Rodents eat fecal pellets to add to fermentation
 Some use size and defensive behaviors to avoid
predation; others keen senses and escape behavior
C. Carnivores
Feed mainly on herbivores; some switch
to fruits, berries when food scarce
Many specializations to kill prey; more
intelligence, stealth, and cunning used
Short digestive tract
More leisure time because do not have to
continuously graze
Humans have exterminated many
carnivores from areas; led to more crop
pests in these areas
D. Omnivores
 Eat plant and animal
tissue—pigs,
raccoons, rats, bears,
primates
 Migration,
hibernation, food
caching used in
temperate areas
where food supplies
become scarce
during certain
seasons
X. Metabolism
 Smaller the animal, greater
metabolic rate and more
must eat per unit size
 Small animals end up
spending more time hunting
and eating than larger
animals
 Small shrews weighing 2 g.
must eat more than this each
day; if deprived of food for a
few hours will die
 Mountain lions need to eat an
average of 1 deer a week
XI. Migration
 Most remain in a
home range, but
some migrate and
most located in North
America
 Caribou migrate100700 miles; gray
whales 11, 250 miles
XII. Flight
Bats fly; some mammals glide
All bats nocturnal so use echolacation to
find food
Echolocation uses high frequency sounds
in pulses that bounce off objects
Large ears help collect “echos and bat
forms mental image of object
Some moths have coevolved to have
ultrasonic detectors to avoid bats
XIII. Reproduction
A. Cycles
 Mating seasons timed to coincide with
favorable time to rear young
 Estrous Cycle—mating restricted to fertile
period in females (estrous or heat) when
ovulation occurs; 1 mating/year (monoestrous);
multiple (polyestrous)
 Sometimes blastocyst remains dormant for
implantation until a more favorable season—
delayed gestation
 Menstrual Cycle—old world monkeys and
humans; cycle terminated by menstruation
when uterine lining is shed
B. Patterns
 Egg-laying—montremes only; egg fertilization
and formation similar to birds but eggs are
leathery; laid once a year in burrow and
incubated; young hatch and nursed from milk
 Pouched—marsupials only; short gestation with
early birth of embryos; mother usually
immediately becomes pregnant with suckling
young still in pouch but development of
embryos arrested (embryonic diapause); long
lactation period
 Placental—long gestation, short lactation
period; embryo in uterus nourished by
placenta; humans slowest developing animal
Forms of Reproduction
XIV.Humans & Mammals
A. Domestication
 Dogs were probably first;
derived from wolves
 Cats from African wildcat
 Subdued horses, oxen,
reindeer, camels,
elephants, and llamas
 Wild versions of llamas
and dromedary camels
no longer exist
 Traits have been
modified through
selective breeding
B. Pests
 Rodents and rabbits
major pests of crops;
elimination of natural
predators has
heightened problem
 Diseases such as
Tularemia, Lyme disease,
and Rocky Mountain
spotted fever transmitted
by ticks on animals such
as rodents, dogs, and
deer
 Tapeworms and trachina
worms transmitted by
eating infected meat
XV. Human Evolution
A. Evolutionary Groups
 Primates—grasping fingers, flat fingernails,
forward facing eyes; split into prosimians &
simians
 Prosimians—dental comb, more projecting face;
lemurs, tarsiers, lorises
 Simians—opposable thumb, some tool use, large
cerebrum; split into monkeys and apes
 Monkeys—Old World located in Africa & Asia,
close set nostrils, advanced dentition (baboon,
mandrill, colobus); New World located in South
America, grasping tail
 Apes--tailless
 Hominids—bipedal, larger cranium, speech
Primates
B. First Hominids
 Grasslands and drought appeared about 8
mya; thought to be selective pressure that
pushed apes out of trees.
 Ardipithecus ramidus—appears about 4.4 mya
with combination of ape/hominid traits
 Australopithecus afarensis—appears about 4
mya; short bipedal hominid; brain size and
facial features similar to chimp
 Australopithicus africanus—appears about 2.2
mya; maybe descendant of A. afarensis and
ancestor to Homo
A. afarensis
H. habilis and A.africanus
H. erectus
C. Emergence of Homo
Found in Africa
Homo habilis—first fully erect hominid that
used stone and bone tools; appeared 2
mya and disappeared 1.5 mya
Homo erectus– appeared 1.5 mya; larger
head and height; spread throughout
Africa, Europe, and Asia; complex
culture;disappeared about 300,000 years
ago
D. Homo sapiens
Homo erectus disappeared about
300,000 years ago
H. neanderthalensis—some consider it a
subspecies; emerged about 130,000
years ago; proficient hunters and tool
users; large nose, big brow ridges, sloping
head; big bones; disappeared about
30,000 years ago
H. sapiens—appear about 100,000 years
ago; more tool using culture; rounded
head, finer features; current people today
H. Erectus and H. sapiens
Neanderthal Man
XIV. Class
Mammalia
A. Order Monotremata
 Egg laying mammals
 Oviparous
Duck billed platypus, spiny
anteater; Australia, New
Guinea & Tasmania
B. Order Marsupiala
 Viviparous
 Pouched
(marsupium)
 Young nourished by
yolk-sac placenta
 Short gestation
 Australia and North
America
 260 species
C. Order Insectivora
 Insect eaters
 Pointy snout
 Live part of time
underground
 Shrews, hedgehogs,
tenrecs, and moles
 All over except
Australia and New
Zealand
 419 species
D. Order Chiroptera
 Flying with modified
forelimbs with
membrane between
elongated fingers
 Bats
 Worldwide
 925 species
E. Order Primates
 Large cerebrum
 Most arboreal
 5 digits with flat nails
on fore- and
hindlimbs; fore- used
for grasping
 Prosimians, monkeys,
apes, humans
 Worldwide
 223 species
F. Order Xenarthra
 Toothless or simple
peg teeth
 Anteateaters,
armadillos, sloths
 South and Central
America
 29 species
G. Order Lagomorpha
 Long constantly
growing incisors
 Additional pair of
peglike incisors
growing behind 1st set
 Herbivores
 Hares, rabbits, pikas
 Worldwide
 80 species
H. Order Rodentia
 2 pairs of incisors used for
gnawing which also grow
constantly
 Extremely adaptable;
fast reproduces
 Comprise 40 % of all
mammals
 Squirrels, rats, mice,
woodchucks, beavers,
porcupines, gophers
 1935 species
I. Order Cetacea
 Forelimbs modified into
broad flippers
 Posterior limbs absent
 Tail divided into flukes;
dorsal fin sometimes
present
 Nostrils modified into
blowhole on top
 No hair except some
hairs around mouth
 Mammary glands only
 Whales, dolphins,
porpoises
 78 species
J. Order Carnivora
 Teeth modified for
eating flesh
 Dogs, cats, bears,
weasels, seals
 Worldwide except
Australia
 280 species
K. Order Proboscidea
 Proboscis (long nose)
 Elongated incisors
forming tusks
 Elephants
 Asia and Africa
 2 species
L. Order Perissodactyla
 Odd-toed hoofed
mammals (1 or 3)
 Ungulate
 Teeth adapted for
chewing
 Horses,asses, zebras,
tapirs, rhinoceroses
 18 species
M. Order Artiodactyla
 Even-toed hoofed
mammals (2 or 4)
 Toe sheathed in hoof
 Ruminants
 Herbivorous
 Swine, camels, deer,
hippos, antelope,
cattle, sheep, goats