CHAPTER 28
Mammals
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Juvenile Grizzly Bear
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Features and Diversity
Features and Diversity

Characteristics
Hair
 Most are placental
 Specialized teeth and jaws for processing
diverse foods in most
 Nervous system more advanced than in
other animal groups
 Mammary glands nourish the newborn
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Features and Diversity
Diversity
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Approximately 4800 living species
Among the most highly differentiated groups
in animal kingdom
Domesticated for use as food, clothing, pets,
beasts of burden, and in research
In 2006, 510 species were listed as “critically
endangered” or “endangered”
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Origin and Evolution of Mammals
History

Mammals are amniotes:
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Amniotes classified as synapsids, anapsids, or
diapsids
Turtles are Anapsids
Mammals are Synapsids
Reptiles and Dinosaurs are Diapsids
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Marsupials
Placental Mammals
Monotremes
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Showing Evolutionary Steps
of the Jaw and Middle Ear Bones
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Evolution of Mammals
Mammal Modifications:
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Evolved a high metabolic rate that supported
a more active life
Enhanced jaw musculature and skeletal
changes for greater agility
A secondary bony palate permits breathing
while holding prey or chewing food
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Important later to mammal evolution by allowing
young to breathe while suckling
Heterodont teeth (varying shapes)
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Improved food processing for variety of foods
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Incisors, canine, molars
Transformation of three middle ear bones
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Malleus, incus, and stapes
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Division allows
breathing and
eating at the same
time.
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Structural and Functional Adaptations of Mammals
Integument and Its Derivatives
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Mammal’s skin generally thicker than in
other vertebrates
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Composed of an epidermis and dermis
Dermis thicker than the epidermis
In regions subject to abrasion, outer layers
of epidermis become thicker and cornified
with keratin
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Structural and Functional Adaptations of Mammals
Hair
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Characteristic of mammals
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May be reduced on some mammals
A hair grows continuously
Cells in hair shaft are shifted upward
away from their source of nourishment,
accumulate keratin, and die
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Keratin is same protein as is found in nails,
claws, hooves and feather
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Structural and Functional Adaptations of Mammals

Dense and soft underhair
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Serves as insulation by trapping a layer of air
Coarse and longer guard hairs
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Protect against wear and provide coloration
American Beavers have tough guard hairs overlying silky underhair.
Valued in the fur trade.
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Structural and Functional Adaptations of Mammals
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In most mammals, there are periodic molts of the
entire coat
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Vibrissae or “whiskers” are sensory hairs
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Foxes and seals shed once every summer
Most mammals molt twice, in the spring and in the fall, with
the winter coat much heavier
Some have white winter coats for camouflage and brown
summer coats
Arctic mammals are not genetically albino where eye and
skin pigments are also missing
Provide a tactile sense for nocturnal mammals
Porcupine, hedgehog, and echidna quills are barbed
and break off easily
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Snowshoe Hare can vary
amount of pigment granules
A: Summer Coat
B: Winter Coat
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Porcupine Quills are
lightly attached so
they can be used
easily. They contain
a hook on the end
that will work it way
into the flesh of the
victim.
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Structural and Functional Adaptations of Mammals
Horns and Antlers
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True Horns - sheep and cattle
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Hollow sheaths of keratinized epidermis
Surround a core of bone rising from skull
Normally not shed and are usually not branched, but
may be curved
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Grow continuously and occur in both sexes
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May be longer in males
Rhinoceros Horn
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Hairlike keratinized filaments arise from dermal
papillae and are cemented together
Not attached to the skull
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Ram with True Horns attached to skull
Rhino with Horn not attached to skull
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Structural and Functional Adaptations of Mammals
Antlers
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Formed in the deer family
Composed of solid bone when mature
Develop beneath an annual spring covering
of soft skin or ”velvet”
Except for caribou, only males produce
antlers
When growth is complete just before
breeding season
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Blood vessels constrict in velvet
Velvet removed by rubbing antlers against trees
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Structural and Functional Adaptations of Mammals
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Antlers are shed after breeding season and a
new bud appears for the next growth
Each year, the new pair of antlers is larger
than the previous set
Growing antlers may require a moose or elk to
accumulate over 50 pounds of calcium salts
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Growth starts late spring.
Growth continues until
rapid increase of testosterone,
causes velvet to fall off.
Breeding Season is in the fall.
Antlers are shed in January as
testosterone levels decrease.
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Structural and Functional Adaptations of Mammals
Glands
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Mammals have the greatest variety of
integumentary gland
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All derived from epidermis
Sweat glands
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Secrete a watery fluid that draws heat away from
the skin surface
Found in hairless regions such as footpads in
most mammals and scattered all over body in
horses and primates
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Sweat glands are reduced or absent in rodents, rabbits
and whales
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Structural and Functional Adaptations of Mammals
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Scent Glands
 Present in nearly all mammals
 Vary in location and function
 Allow for communicate with members of the
same species
 Mark territory, warning and defense signals
 Scent glands of skunks, minks, and weasels
open into the anus and have a strong odor
 Many mammals release strong scents during
the mating season to attract opposite sex
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Structural and Functional Adaptations of Mammals

Sebaceous Glands
 Most associated with hair follicles
 May open directly onto the skin surface
 Glandular cells produce an oily secretion,
sebum
 Lubricates skin and hairs
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Makes skin look shiny and attractive
Waterproof
Most mammals have sebaceous glands over
the entire body
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Structural and Functional Adaptations of Mammals
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Mammary Glands
 Not fully developed in males and occur on all
females
 Human females develop mammary glands at
puberty
 Other mammals have swollen mammary
periodically when pregnant or nursing
 In most mammals milk is secreted from mammary
glands via nipples or teats
 Exception: Monotremes lack nipples and simply
secrete milk into a depression on the mother’s
belly where it is lapped up by young
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Structural and Functional Adaptations of Mammals
Food and Feeding
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Mammals exploit a wide variety of food
sources
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Some are specialists and others are generalists
Teeth
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Structure of teeth reveal the habits of a mammal
Reptiles have homodont dentition or uniform
tooth patterns
Differentiation of teeth for cutting, seizing,
gnawing, etc., resulted in heterodont dentition
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Feeding specializations among mammals
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Structural and Functional Adaptations of Mammals
Incisors: Sharp edges for snipping or
biting
 Canines: Specialized for piercing
 Premolars: Crowns with one or two cusps
for shearing and slicing
 Molars: Larger bodies and variable cusp
arrangements for crushing and grinding
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Structural and Functional Adaptations of Mammals
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Feeding Specializations
 Insectivores
Shrews, moles, anteaters, and most bats
 Due to limited ingestion of fibrous vegetable
matter, digestive tract is short
 Feed primarily on insects
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Structural and Functional Adaptations of Mammals
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Herbivores
Cellulose is a chain of glucose molecules,
difficult to break
 A side pocket or cecum may serve as a
fermentation chamber and absorptive area to
help break down cellulose
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Browsers and grazers include horses, deer, antelope,
cattle, sheep, and goats
Gnawers include rodents, rabbits, and hares
Herbivores have reduced or absent canines
 Rodents have chisel-shaped incisors that grow
throughout life
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
Ruminants have a large, four-chambered stomach
 Food is regurgitated, re-chewed, and passed to the
rumen, and 3 more chambers
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cattle, goats, sheep, giraffes, bison, yaks, water buffalo,
deer, camels, alpacas, llamas, wildebeest, antelope
Herbivores generally have long digestive tracts for the
prolonged time needed to digest fiber (cellulose)
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Structural and Functional Adaptations of Mammals

Carnivores
Most feed on herbivores
 Requires specialization for killing prey
 High protein diet is easily digestible and,
therefore, the digestive tract is shorter
 Capturing prey also requires more intelligence,
stealth, and cunning
 Some herbivores use size (i.e., rhinos,
elephants) or defensive group behaviors
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28-35
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Lions gorge themselves after a kill.
Then they may not eat again for a week.
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Structural and Functional Adaptations of Mammals

Omnivores
Feed on both plant and animal tissues
 Include pigs, raccoons, rats, bears, and most
primates including humans
 Many carnivores will switch to fruits, berries,
etc. when other food sources are scarce
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Eastern Chipmunk:
Cheeks stuffed with seeds
to be hidden. It will store
several liters of food
for the winter hibernation.
It will hibernate but wake
periodically for food.
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Structural and Functional Adaptations of Mammals

Body Weight and Food Consumption
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The smaller the animal, the greater is its
metabolic rate
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Requires more food per unit size
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Shorttail Shrew - spend most of its time below ground.
Feeds on insects, mice, snails, and worms.
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Structural and Functional Adaptations of Mammals
Migration
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Few terrestrial mammals make regular
seasonal migrations
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Most remain in a home range
More migratory animals in North America
than any other continent
Caribou migrates twice each year, spanning
160–1100 kilometers (100–700 miles)
Gray whales migrate 18,000 kilometers
(11,250 miles) between Alaska and Baja,
Mexico annually
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Adult Male Caribou w/ Autumn velvet antlers
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Summer and Winter ranges of some major caribou herds.
Arrows show spring migration routes.
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Annual Migration of Northern fur seals. Separate wintering grounds for male
and females. In early summer months both males and females migrate to
Pribilof Islands to give birth and then mate again. Then they separate.
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Structural and Functional Adaptations of Mammals
Flight and Echolocation
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Mammals have not exploited the skies
extensively
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Bats can fly and some mammals glide from trees
Bats are nocturnal (active at twilight)
Echolocation, along with flight, allows bats
to navigate and eat insects in total darkness
Bats inhabit totally dark deep caves, a
habitat ignored by other mammals and birds
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Northern Flying
Squirrel. Glide
40-50 meters,
using gliding
skin and special
muscles.
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Structural and Functional Adaptations of Mammals
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Bats use frequencies well beyond our hearing
range
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Similar to yelling into an canyon, and echo comes
back
Bats project a sound wave which will “echo” on
contact with a prey
External ears of bats are large to focus in on
sound location
Bat navigation may allow bats to build mental
image of surroundings similar to visual
images
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Brown Bat - Echolocation
28-47
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Structural and Functional Adaptations of Mammals
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All bats are nocturnal
Fruit-eating bats use sight and smell to
locate food
Some flowers evolved to utilize bats as
pollinators
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Produce fragrant white flowers that open at night
Vampire bat has razor-sharp incisors and
anticoagulant saliva
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Bite Prey, then lick up dripping blood
Also regurgitate blood for fellow bats that can’t find food
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Dolphins also use echolocation. They make a “clicking” noise by moving
air through their nasal cavity. Returning sounds are received by mandible,
and passed to the inner ear.
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Structural and Functional Adaptations of Mammals
Reproduction
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Reproductive Cycles
Estrous Cycle
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mating seasons timed to coincide with most favorable time
to give birth and rear young
Female usually restrict mating to a fertile period during the
estrus cycle
 Commonly called heat or estrus
Some animals lengthen gestation period by delayed
implantation
 Blastocyst remains dormant
 Implantation in the uterine wall is postponed to align
birth with a favorable season
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Structural and Functional Adaptations of Mammals
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Animals with only one breeding season a year are
monestrous
Recurrent breeding is polyestrous
Menstrual Cycle
 Old World monkeys and humans have a cycle
terminated by menstruation
 Menstruation involves shedding of the
endometrium or lining of the uterus
 Female is receptive to male year round
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Structural and Functional Adaptations of Mammals

Reproductive Patterns
Egg-Laying monotremes
 Monotremes, such as the duck-billed platypus, lay
eggs with one breeding season per year
 Eggs are fertilized in oviduct before a thin,
leathery shell is added
 Eggs are layed in a burrow nest and incubated for
12 days
 No gestation period and egg provides all nutrients
 After hatching, young nourished by milk lapped
off mother’s fur near mammary glands - no
nipples
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Structural and Functional Adaptations of Mammals
Pouched Marsupials
 Pouched, viviparous mammals
 Embryo is first encapsulated by shell membranes
and floats free in uterus for several days
 After “hatching” from shell membranes, embryo
wears away a shallow depression in the uterine
wall and absorbs nutrients
 Gestation is brief and marsupials give birth to tiny
young that are still embryos
Which is a faster method for adults to produce
independent young? Monotremes or marsupials?
Meaning, which young develop faster?
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Comparison of gestation and lactation periods between marsupials and placental mammals
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Structural and Functional Adaptations of Mammals
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Early birth is followed by a prolonged interval of
lactation and parental care in mother’s pouch
In red kangaroos
 Pregnancy is followed by a 33-day gestation and
then birth
 Mother immediately becomes pregnant again
 Presence of a suckling young arrests
development of the new embryo at the 100-cell
stage
 Period of arrest is called embryonic diapause
 Possible to stairstep three young with one
external, one suckling, and one embryonic
With wide variation, marsupials have young born at
extremely early stages of development
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Kangaroos may have three young in different stages of development, all dependent on her.
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Southern Opossums:
Gestation period - 12 days
Attached to nipple - 55 days
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Structural and Functional Adaptations of Mammals
Placental Mammals
 Embryo nourished in uterus through a placenta
 Gestation is longer than in marsupials and is
much longer for large mammals
 Gestation and body size are loosely correlated
due to variation in maturity at birth
 Humans have slower developmental period than
any other mammal
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Structural and Functional Adaptations of Mammals
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Patterns
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Number of young produced per year depends on
mortality rate
Small rodents that are prey for carnivores usually
produce more than one litter each season
Meadow mice can produce up to 17 litters of four
to nine young each year
An elephant produces on average four calves
during her 50-year life
Although placentals have the advantage of higher
reproductive rates
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Structural and Functional Adaptations of Mammals

Territory and Home Range
 An animal may use a burrow or den as the center
of its territory
 If it has no set address, the territory is marked,
usually with scent glands
 A grizzly bear may have a territory of several
square kilometers that it defends against other
grizzlies
 When an intruder knows it is in another’s territory,
it usually flees upon an encounter
28-60
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Beavers construct a colony. Mother bears 4-5 young each litter. When the 3rd litter
arrives, 2-year old young are driven out to start their own colony.
28-61
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Human Evolution
History


Two skeletons of Neanderthals were
collected in the 1880s - now Neanderthals are
linked to European descent
Modern biochemical studies have also
shown humans and chimpanzees to be
genetically similar (99.2%)
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Human Evolution
Evolutionary Radiation of the Primates


Primates have grasping fingers, flat
fingernails, and forward-pointing eyes
Ancestral primates split into two major
lineages
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
One gave rise to lemurs and relatives (traditionally
called prosimians)
The other gave rise to monkeys and apes
(traditionally called simians)
Both were probably arboreal (tree- dwellers)
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Required a large cerebral cortex (for precise
timing, judgement of distance, etc.), grasping
limbs, and tool use
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Tarsier Prosimian
28-64
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Human Evolution

Three major simian groups
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
New World monkeys of Central and South America
including howler monkeys, spider monkeys, and
tamarins - have grasping tail
Old World monkeys including the baboon, mandrill,
and colobus - lack grasping tail, better opposable
thumbs
Humans, orangutans, chimps, and gorillas
(Hominids- Apes)
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
28-65
No tail, larger cerebrum
Apes first appear in 25-million-year-old fossils
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Primates:
Old World Monkey - 30 mya
Olive Baboon
Primates:
New World Monkeys - 40 mya
Howler Monkeys
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28-66
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Primate:
Hominid - 20 mya
Gorilla - 6-8 mya
Chimp - 500,000
Human - 200,000
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Human Evolution
Early Humans
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5 mya, grasslands replaced forests in eastern
Africa
The Savannah Hypothesis
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Proposes that standing upright provided a better
view of predators, freed hands for using tools,
aided in defense and care of young, and improved
food gathering
Upright posture required extensive
redesigning of the skeleton and muscle
attachments
Four million year old "Near human" fossils
discovered (Lucy)
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Human Evolution

Lucy
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Short, bipedal hominid
Brain size similar to that of a chimpanzee
Numerous fossils of species have been
discovered, including “Lucy” in 1974
4 mya
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Reconstruction of the
appearance of Lucy,
compared with modern
Human (left)
In
2001, a remarkably
complete skull of a hominid
dated at nearly 7 million
years ago was discovered in
Chad
Most ancient hominid
yet discovered
28-70
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Evolutionary lines preceding
Modern humans (Homo sapiens)
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