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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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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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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


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Turbinate bones in

the nasal cavity

aided in the retention

of heat.

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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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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.

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