28. mammals (1)
TRANSCRIPT
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Mammals
Chapter 28
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Class Mammalia
Mammals, class
Mammalia, are
represented by more
than 5,000 species. Kittis hognosed bat
from Thailand
weighs 1.5 g.
Blue whales exceed130 metric tons.
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Derived Characters of Mammals
Mammary glands, which produce milk
are a distinctively mammalian character.
Hairis another mammalian
characteristic.
Mammals generally have a larger brain
than other vertebrates of equivalent size.
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Early Evolution of Mammals
Mammals evolved from synapsids in the
late Triassic period.
The earliest synapsids radiated into diverse
herbivorous & carnivorous forms the
pelycosaurs.
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Early Evolution of Mammals
One group of
carnivorous
pelycosaurs led to
the therapsids. The only synapsid
group to survive
into the Mesozoic.
Limbs positionedunder the body.
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Early Evolution of Mammals
Cynodonts were a group of therapsid
reptiles that radiated in the Mesozoic.
One branch of cynodonts eventually led to
the early therians (marsupial and placental
mammals).
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Cynodonts evolved:
A high metabolic rate that supported a moreactive life.
Enhanced jaw musculatureA secondary bony palate permits breathing
while holding prey or chewing food. Important later to mammal evolution by allowing
young to breathe while suckling
Early Evolution of Mammals
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Early Evolution of Mammals
Turbinate bones in
the nasal cavity
aided in the retention
of heat.
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Early Evolution of Mammals
The jaw wasremodeled duringthe evolution ofmammals fromnonmammaliansynapsids.
Two of the bonesthat formerly made
up the jaw jointwere incorporatedinto the mammalianmiddle ear.
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Early Evolution of Mammals
Living lineages of
mammals originated
in the Jurassic, but
did not undergo asignificant adaptive
radiation until after
the Cretaceous.
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Skin & Hair
Skin is composed of the
thinnerepidermis and
the underlying, thicker
dermis.
Hairis one of the
defining characteristics
of mammals.
Composed of dead,
keratin-packedepidermal cells.
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Hair
Two kinds of hair form the coat of most
mammals:
Dense and soft underhairfor insulation.
Traps a layer of insulating air.
Extremely dense in aquatic mammals.
Coarse, longerguard hairfor protection
from wear and coloration.
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Hair
Mammals shed or
molt once or usually
twice each year.
Summer coatusually thinner.
May be a different
color.
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Hair
Hair can be specialized
into bristles, spines, and
whiskers.
Whiskers, vibrissae,are sensory hairs that
provide tactile sense to
many mammals.
Especially long innocturnal and burrowing
mammals.
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Horns & Antlers
Horns, like those of sheep & cattle, are
hollow sheaths of keratinized epidermis
with a core of bone.
Found in both sexes, grow continuously, are
not shed.
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Horns & Antlers
Antlers, like those ofdeer, are branched andcomposed of solidbone.
During growth, theyhave a highly vascularsoft skin called velvetcovering them.
Usually only maleshave antlers. Both sexes of Caribou
have antlers.
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Glands
Mammals have the greatest variety of
integumentary glands of any vertebrate.
Sweat glands involved in heat regulation.
Scent glands for marking territories,
warning, defense.
Sebaceous glands associated with hair
follicles. Mammary glands provides milk for
offspring, gives mammals their name.
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Food and Feeding
Mammals eat
a wide variety
of food.
Dentitionoften reflects
the food they
eat.
Heterodont
dentition
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Food and Feeding
Mammals also haveadaptations that helpthem digest thedifferent types offoods they eat.
Herbivores cantdigest cellulosethey rely on
microorganisms tometabolizecellulose.
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Body Weight and Food
Consumption
The smaller the
animal, the higher its
metabolic rate.
More food must beconsumed.
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Migration
Some terrestrial mammals, like caribou and
bison, migrate twice annually between summer
and winter ranges.
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Migration
Migration is
more
common
amongoceanic
whales &
seals.
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Flight and Echolocation
Many mammals
can glide from
tree to tree.
Not poweredflight.
Gliding & flying
evolved
independently.
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Flight and Echolocation
Bats have evolved true flight.
Mostly nocturnal or crepuscular.
Echolocation is used to navigate and locate
food.
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Territoriality
Many mammals defend a territory that
includes resources such as food, shelter,
or mates that is defended from others
usually of the same species(conspecifics) those that would utilize
the same resources.
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Territoriality
A mammal usually has a larger,
undefended home range that may
overlap with the home range of
conspecifics.
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Monotremes
Monotremes are a small group of egg-laying
mammals consisting of echidnas and the
platypus.
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Monotremes
Monotremes are oviparous mammals.
Eggs have a thin, leathery shell.
Babies hatch in a relatively undevelopedstate.
Echidnas have an abdominal pouch
where they keep the young.
Young feed on milk secreted by the
mothers mammary glands.
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Marsupials
Marsupials
include opossums,
kangaroos, and
koalas.
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Marsupials
Before it is a born, an embryonic
marsupial receives nourishment by
absorbing nutrient secretions in the
uterus.
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Marsupials
A marsupial is
born very early in
its development
and completesits embryonic
development
while nursing
within a maternalpouch called a
marsupium.
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Convergent Evolution
In Australia,
convergent evolution
has resulted in a
diversity ofmarsupials that
resemble
eutherians
(placental mammals)in other parts of the
world.
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Eutherians Placental Mammals
Compared tomarsupials,
eutherians have
a longer period of
pregnancy.
Usually larger
placental
mammals havelonger
gestations.
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Eutherians Placental Mammals
Young eutherians complete their
embryonic development within a uterus,
joined to the mother by the placenta.
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Primates
The mammalian order Primates
include:
Lemurs, tarsiers, monkeys, and apes
Humans are members of the ape group.
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Primates
Most primates have hands and feetadapted for grasping.
Primates also have:
A large brain and short jaws. Forward-looking eyes close together on the
face, providing depth perception.
Well-developed parental care and complexsocial behavior.
A fully opposable thumb.
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Living Primates
There are three main
groups of living
primates:
The lemurs ofMadagascar and
the lorises and
pottos of tropical
Africa and southernAsia form one
group.
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Living Primates
The tarsiers of
Southeast Asia.
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Living Primates
The anthropoids,
which include
monkeys and
hominids worldwide.
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Primate Evolution
The oldest known
anthropoid fossils
are about 45 million
years old. Indicate that
tarsiers are more
closely related to
anthropoids.
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Primate Evolution
The fossil record
indicates that monkeys
first appeared in the
New World (SouthAmerica) during the
Oligocene (~36 mya).
The first monkeys
evolved in the OldWorld (Africa and Asia)
about 40 mya.
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Primate Evolution
New World and Old World monkeys
underwent separate adaptive radiations during
their many millions of years of separation.
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Primate Evolution
The other group ofanthropoids, thehominoids,consists of primates
informally calledapes.
Hominoids divergedfrom Old World
monkeys about 2025 million yearsago.
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Primate Evolution
African apes chimpanzees & gorillashave been moved into the familyHominidae to more accurately reflect
relatedness. So, now, humans, chimps and gorillas are
hominids.
Many researchers advocate placing
them in the genus Homo as well.
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Humans Bipedal Hominoids
Homo sapiens is about 200,000 years
old which is very young considering that
life has existed on Earth for at least 3.5
billion years.
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Derived Characters of Hominids
A number of characters distinguish
humans from other hominoids:
Upright posture and bipedal locomotion
Larger brains
Language capabilities
Symbolic thought
The manufacture and use of complex tools
Shortened jaw
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Human Origins
The study of human origins is known as
paleoanthropology.
Paleoanthropologists have discovered
fossils of approximately 20 species of
extinct hominoids that are more closely
related to humans than to chimpanzees.
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Human Origins
October 2, 2009 issue of
Science is full of articles on
Ardipithicus ramidus.
Available for free!
http://www.sciencemag.org/
ardipithecus/
http://www.sciencemag.org/ardipithecus/http://www.sciencemag.org/ardipithecus/http://www.sciencemag.org/ardipithecus/http://www.sciencemag.org/ardipithecus/ -
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Human Origins
Hominins (modern humans and their
extinct ancestors are placed in the
subfamily Homininae) originated in Africa
approximately 67 million years ago.
Early hominins had a small brain, but
probably walked upright, exhibiting
mosaic evolution (different traitsevolving at different rates).
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Human Origins
Two common misconceptions of early
hominids include:
Thinking of them as chimpanzees.
Imagining human evolution as a ladder
leading directly to Homo sapiens.
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Human Origins
Australopiths are a paraphyletic
assemblage of hominids that lived
between 4 and 2 million years ago.
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Human Origins
Some species walked fully erect and had
human-like hands and teeth.
Australopith brains were smaller than modern
humans, but larger than chimps.
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Bipedalism
Hominins began to
walk long distances
on two legs about
1.9 million yearsago.
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Tool Use
The oldest evidence of tool use cut
marks on animal bones is 2.5 million
years old.
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Early Homo
The earliest fossils that
paleoanthropologists place in our genus,
Homo, are those of the species Homo
habilis, ranging in age from about 2.4 to1.6 million years.
Stone tools have been found with H.
habilis, giving this species its name,which means handy man.
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Early Homo
Homo ergasterwasthe first fully bipedal,
large-brained
hominin. Existed between 2
and 1.4 million
years.
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Early Homo
Homo erectus originated in Africaapproximately 1.8 million years ago.
The first hominin to leave Africa.
Social living in tribes of 20-50.
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Neanderthals
Neanderthals, Homo neanderthalensislived in Europe and the Near East from
200,000 to 30,000 years ago.
Large, thick-browed hominins.
Became extinct a few thousand years after
the arrival ofHomo sapiens in Europe.
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Homo sapiens
Homo sapiensappeared in Africa at
least 200,000 years
ago.
H i
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Homo sapiens
The rapid expansion of our species may have been
preceded by changes to the brain that made symbolic
thought and other cognitive innovations possible.
Binocular vision, visuotactile discrimination and
manipulative skills that resulted from our arborealancestry likely played a role as well.