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PLACENTAL MAMMALS
CLASSIFICATION
• Order Primates:
– 200 species:
• Prosimians: lemurs, tarsiers, and lorises
• Anthropoids: monkeys, apes, and humans
– Most are omnivores with teeth specialized
for a varied diet
– Most tend to live in social groups
PRIMATE
PRIMATE
Biogeography of Mammals
• The history of Earth's geography has helped
shape today's mammals
• During the Paleozoic Era, the continents
were one large landmass, and mammals
could migrate freely across it
• But as the continents drifted farther and
farther apart during the Mesozoic and early
Cenozoic Eras, ancestors of mammal groups
were isolated from one another
• Each landmass took with it a unique array of
mammal groups
Biogeography of Mammals
• Similar ecological opportunities on the
different continents have produced some
striking examples of convergent evolution in
mammals
– Thousands of kilometers apart, mammals evolved
similar adaptations in form and function
• When some of the landmasses merged in the
late Cenozoic Era, mammals dispersed and
intermingled in new habitats
• Living mammals reflect the diversity that resulted
from these events.
Convergent Evolution
• Similar ecological
opportunities on different
continents have resulted in
convergent evolution among
these and other mammals
• Mammals that feed on ants
and termites evolved not once
but five times in different
regions
• Powerful front claws; a long,
hairless snout; and a tongue
covered with sticky salvia are
common adaptations in these
insect-eating animals
Convergent Evolution
CONVERGENT EVOLUTION
Primates and Human Origins
• Our own species, Homo sapiens, belongs
to the order that also includes lemurs,
monkeys, and apes
• Carolus Linnaeus named our order
Primates, which means “first” in Latin
What Is a Primate?
• Just what are primates “first” in?
• When the first primates appeared, there
was little to distinguish them from other
mammals besides an increased ability to
use their eyes and front limbs together
to perform certain tasks
• As primates evolved, however, several
other characteristics became distinctive
What Is a Primate?
• Primates share several important
adaptations, many of which are extremely
useful for a life spent mainly in trees
• In general, primates have:
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Binocular vision
Well-developed cerebrum
Relatively long fingers and toes
Arms that can rotate around their shoulder joints
HUMAN EVOLUTION
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Paleoanthropologists: scientists who study human evolution
Classification of Humans:
– Class: Mammalia
– Order: Primates (erect mammal)
• Opposable thumb: ability to grasp
• Flattened nails rather than claws
• Forward facing eyes: stereoscopic vision
• Color vision (cones in retina)
• Periodic vertical positioning (upright erect posture)
• Shrews, Tarsiers, Lemurs, Monkeys, Apes (gibbons, chimpanzees,
orangutans, gorillas), humans
– Subgroup: Anthropoids (monkeys, apes, humans)
» Welled developed collarbone, rotating shoulder joints, and
partially rotating elbow joints gives skeletal strength and
flexibility
» Opposable thumb
» Larger brain (cerebrum) (increase cranial capacity)
TARSIER
GIBBON
CHIMPANZEE
GORILLA
HUMAN EVOLUTION
• Human Characteristics:
– Bipedalisms: upright walking on two legs (unique human trait)
– Broader Pelvis allowing for bipedal posture and supporting internal
organs
– Foramen Magnum: opening in the skull where the spinal cord enters is
at the very bottom of the skull
• Allows the vertebral column to support the head during bipedal walking
• Sockets of pelvis positioned so that the leg bones extend vertically
downward
• Central opening larger in female
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Larger cranial capacity (1400 cc)
Vertical forehead
Opposable thumb capable of moving farther across the hand
Big toe aligned with other toes helping distribute body weight during
upright walking
– V-shaped jaw (round shape)
– No spacing between smaller teeth (omnivores)
Fingers, Toes, and Shoulders
• Primates normally have five flexible fingers that can
curl around objects
• Most also have flexible toes
• Flexible digits (fingers and toes) enable many primates
to run along tree limbs and swing from branch to branch
with ease
• Primates' arms are well adapted to climbing because
they can rotate in broad circles around a strong
shoulder joint
• In most primates, the thumb and big toe can move
against the other digits
– The presence of this adaptation allows many primates to hold
objects firmly in their hands or feet
HUMAN EVOLUTION
HUMAN EVOLUTION
Well-Developed Cerebrum
• The large and intricate cerebrum of
primates—including a well-developed
cerebral cortex—enables them to
display more complex behaviors than
many other mammals
• For example, many primate species have
elaborate social behaviors that include
adoption of orphans and even warfare
between rival primate troops
HUMAN EVOLUTION
Binocular Vision
• Many primates have a flat face, so both eyes
face forward with overlapping fields of view
– This facial structure gives primates excellent
binocular vision
• Binocular vision is the ability to merge visual
images from both eyes, thereby providing
depth perception and a three-dimensional
view of the world
• This is a handy adaptation for judging the
locations of tree branches, from which many
primates swing
TARSIER
Evolution of Primates
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Humans and other primates evolved from a common ancestor that lived
more than 65 million years ago
Early in their history, primates split into several groups
Primates that evolved from two of the earliest branches look very little
like typical monkeys and are called prosimians
Members of the more familiar primate group that includes monkeys,
apes, and humans are called anthropoids
Primate Evolution
• This diagram illustrates the phylogeny of modern
primates
• The two main groups of primates are prosimians
and anthropoids
Primate Evolution
Prosimians
• With few exceptions, prosimians alive
today are small, nocturnal primates
with large eyes that are adapted to
seeing in the dark
– Many have doglike snouts
• Living prosimians include the bush babies
of Africa, the lemurs of Madagascar, and
the lorises and tarsiers of Asia
Anthropoids
• Humans, apes, and most monkeys belong to a group called
anthropoids, which means humanlike primates
• This group split very early in its evolutionary history into two
major branches: These branches became separated from each
other as drifting continents moved apart
– One branch, found today in Central and South America, is called
the New World monkeys
• After Columbus's voyage to America, Europeans began to use the term New
World to refer to North and South America
• New World monkeys, which include squirrel monkeys and spider monkeys,
live almost entirely in trees
• These monkeys have long, flexible arms that enable them to swing from
branch to branch
• New World monkeys also have a long, prehensile tail
– A prehensile tail is a tail that can coil tightly enough around a branch to
serve as a “fifth hand”
Anthropoids
• The other anthropoid group, which evolved in Africa
and Asia, includes the Old World monkeys and great
apes
– Old World monkeys, such as langurs and macaques, spend
time in trees but lack prehensile tails
• Great apes, also called hominoids, include gibbons,
orangutans, gorillas, chimpanzees, and humans
• Recent molecular studies confirm that chimpanzees
are humans' closest relatives among the great apes
– Humans and chimps share an astonishing 98 percent of
their DNA!
Hominid Evolution
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Between 6 and 7 million years
ago, the hominoid line gave rise
to a branch that ultimately led
to the ancestors and closest
relatives of modern humans
The hominid family, which
includes modern humans,
displayed several distinct
evolutionary trends
Fossil evidence shows that as
hominids evolved over millions of
years, they became able to walk
upright and developed thumbs
adapted for grasping
They also developed large brains
Hominid Evolution
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The skull, neck, spinal column,
hipbones, and leg bones of
early hominid species changed
shape in ways that enabled later
species to walk upright
The figure at right shows some
ways in which the skeletons of
modern humans differ from those
of gorillas
The evolution of this bipedal, or
two-foot, locomotion was very
important, because it freed both
hands to use tools
Meanwhile, the hominid hand
evolved an opposable thumb
that enabled grasping objects
and using tools
Hominid Evolution
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Hominids also displayed a
remarkable increase in brain
size
Chimpanzees, our closest living
relatives among the apes, have a
brain size of 280 to 450 cubic
centimeters
The brain of Homo sapiens, on
the other hand, ranges in size
from 1200 to 1600 cubic
centimeters!
Most of the difference in brain
size results from an enormously
expanded cerebrum—the
“thinking” area of the brain
Human and Gorilla Skeletons
• Modern hominids
walk upright on two
legs; gorillas use all
four limbs
• According to the chart
and illustration, what
are the other
differences between
humans and gorillas?
Human and Gorilla Skeletons
Early Hominids
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Paleontologists have unearthed a treasure trove of hominid species
At present, most paleontologists agree that the hominid fossil record
includes at least these genera—Ardipithecus, Australopithecus,
Paranthropus, Kenyanthropus, and Homo—and as many as 20
separate species
This diverse group of hominid fossils covers roughly 6 million years
All these species are relatives of modern humans, but not all of them
are human ancestors
– To understand that distinction, think of your family
• Your relatives may include aunts, uncles, cousins, parents,
grandparents, and great-grandparents
• Of these, only your parents, grandparents, and greatgrandparents are your ancestors
HOMINID EVOLUTION
• Hominids: subgroup of primates that includes
human beings (Homo sapiens) and their
immediate ancestors
– Fossil record indicates a trend toward:
• Bipedalism
• Increased cranial capacity
• Evolution of culture:
– indicative of behavior that is dependent on learning and on
passing knowledge from one generation to the next
– Culture is all the information and ways of living built up by a
group of human beings
» Passed from one generation to the next
Early Hominids
• Almost a third of all known hominid species have been
discovered in the last 20 years
• This shows how rapidly knowledge of hominid fossils is
growing
• It also explains why hominid evolution is both fascinating
and confusing
• What once looked like a simple “human family tree”
now looks more like a dense, branching shrub
• Many questions remain about how fossil hominids are
related to one another and to humans
• Let's examine a few of the most important discoveries
Human-Fossil Seekers
HOMINID EVOLUTION
• Australopithecus:
– Earliest genus of hominids
– Means “southern ape”
– First found in South Africa
– No evidence of tools
– Four species:
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Australopithecus afarensis
Australopithecus africanus
Australopithecus robustus
Australopithecus boisei
AUSTRALOPITHECUS
Australopithecus
• One early group of hominids, members of the
genus Australopithecus, lived from about 4
million to a million years ago
• These hominids were bipedal apes that spent
at least some time in trees
• The structure of their teeth suggests a diet
rich in fruit
• Some Australopithecus species seem to
have been human ancestors, while others
formed separate branches off the main
hominid line
Australopithecus
• The best known species is Australopithecus
afarensis—described from a remarkably
complete female skeleton, nicknamed Lucy,
who stood only about 1 meter tall
• The humanlike footprints, which are between 3.8
and 3.6 million years old, were probably made
by members of the same species as Lucy
• Since Australopithecus fossils have small
brains, the Laetoli footprints show that
hominids walked bipedally long before large
brains evolved
Australopithecus Footprints
• Between 3.8 and 3.6
million years ago,
members of a species
of Australopithecus
made these footprints
at Laetoli in Tanzania
• The footprints show
that hominids walked
upright millions of
years ago
Australopithecus Footprints
AUSTRALOPITHECUS
HOMINID EVOLUTION
• Australopithecus afarensis:
– Oldest fossil dated between 3 million and
3.5 millions years old (Lucy)
– Shorter than modern humans
(approximately 1.5m or 5 ft tall)
– Bone structures indicate bipedalism
– Cranial capacity between 380 and 450 cc
(1/3 modern humans)
HOMINID EVOLUTION
• Australopithecus africanus:
– Lived 2.2 million to 3 million years ago
– Slightly taller and heavier than A. afarensis
– Cranial capacity slightly larger than A.
afarensis: between 430 and 550 cc
HOMINID EVOLUTION
• Australopithecus robustus:
– Southern Africa
• Australopithecus boisei:
– Eastern Africa
• Both species:
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Lived between 1 million and 2 million years ago
Heavier skulls than A. africanus
Larger back teeth than A. africanus
Larger cranial capacity than A. africanus: between
450 and 600 cc
Paranthropus
• Three later species, which grew to the size of wellfed football linebackers, were originally placed in the
genus Australopithecus
– However, they are now usually placed in their own
genus, Paranthropus
• The known Paranthropus species had huge, grinding
back teeth
• Their diets probably included coarse and fibrous
plant foods like those eaten by modern gorillas
• Most paleontologists now place Paranthropus on a
separate, dead-end branch of our family tree
Recent Hominid Discoveries
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Early in 2001, a team led by
paleontologist Meave Leakey
announced that they had
uncovered a skull in Kenya
Its ear structures resembled
those of chimpanzees, and its
brain was rather small
Yet some of its facial features
resembled those of fossils
usually placed in the genus
Homo
Paleontologists put this skull in a
new genus, Kenyanthropus.
Kenyanthropus is shown in the
middle in the figure at right
Evidence indicates that this
species existed at the same time
as A. afarensis
Recent Hominid Discoveries
• Then, during the summer of
2002, paleontologists
working in the desert in
north-central Africa
announced the discovery of
an even more startling skull
• This fossil skull, tentatively
called Sahelanthropus, is
nearly 7 million years old
• If scientists agree that
Sahelanthropus is indeed a
hominid, it would be a million
years older than any hominid
previously known
Recent Hominid Discoveries
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Sahelanthropus had a brain
about the size of a modern
chimp, yet its short, flat face is
more like that of a human
In fact, this skull seems more
humanlike in certain ways than
Lucy (A. afarensis), who lived
several million years later
While most hominid fossils
have been discovered in
eastern Africa, Sahelanthropus
was discovered much farther to
the west
This suggests that there may be
many more fossil hominids to
be found in widely separated
parts of Africa
HOMINID EVOLUTION
• Homo habilis:
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Means “handy human”
Cranial capacity between 600 to 800 cc
Made and used stone tools
Found in southern and eastern Africa
Lived between 1.6 and 2 million years ago
Region of brain essential to speech was
developed in this species
– Tool marks on animal bones indicated that they
ate meat
– No taller than Australopithecines
HOMINID EVOLUTION
• Homo erectus:
– Means “upright human”
– Found in many parts of the world (first found on the Pacific island
of Java)
– Lived between 0.5 million and 1.6 million years ago
– Compared to modern humans:
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Skull is thicker
Large brow ridges
Low forehead
Very small chin
Cranial capacity between 700 and 1,250 cc
Tall as modern man
Used fire for cooking and warmth
Used modified finely crafted stone tools
Lived in groups
HOMO ERECTUS
HOMO ERECTUS
Hominid Skulls
• Paleontologists’ interpretations
of hominid evolution are based
on he study of fossils such as
these skulls—Sahelanthropus
tchadensis (left),
Kenyanthropus platyops
(middle), and Homo erectus
(right)
• Sahelanthropus may be the
earliest known hominid
• Which of these skulls most
closely resembles the skull of
a modern human?
Hominid Skulls
Rethinking Early Hominid
Evolution
• Together with other recent fossil finds, the discovery of
Kenyanthropus and Sahelanthropus have dramatically changed the
way paleontologists think about hominid evolution
• Researchers once thought that human evolution took place in
relatively simple steps in which hominid species, over time,
became gradually more humanlike
• It is now clear that hominid evolution did not proceed by the
simple, straight-line transformation of one species into another
• Rather, like the evolution of other mammalian groups, a series
of complex adaptive radiations produced a large number of
species whose relationships are difficult to determine
• Which hominids are true human ancestors?
• Which are just relatives?
• And how are all those species related to one another and to
modern humans?
• At present, no one can answer these questions
Rethinking Early Hominid
Evolution
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So what is known about hominid
evolution?
As shown in the figure at right,
the hominid fossil record now
dates back nearly 7 million
years, close to the time that
DNA studies suggest for the
split between hominids and the
ancestors of modern
chimpanzees
In addition, there are many known
fossil hominid species, several of
which display a confusing mix of
primitive and modern traits
It will probably take many years of
work to more fully understand this
fascinating and complex story
Hominid Evolution
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The diagram shows fossil hominids
and the time ranges during which
they may have existed
The time ranges are likely to change
as paleontologists gather new data
The question mark after
Sahelanthropus tchadensis
indicates that scientists are not yet
certain that this species is a
hominid
Paleontologists do not yet have
enough information to know how
hominid species are related
It is now clear that hominid
evolution did not proceed by the
simple, straight-line transformation
of one species into another
Current hypotheses about early
stages of human evolution
recognize the incompleteness of
the data
Hominid Evolution
HOMINID EVOLUTION
• Homo sapiens: “thinking human”
– Neanderthals:
• Fossils from 35,000 and 130,000 years ago found in Europe, Asia,
and Africa
• Early Homo sapiens
• Heavy bone
• Thick brow ridges
• Small chin
• Cranial capacity: 1,450 cc (slightly larger than cranial capacity of
modern humans)
• 1.5m or 5ft tall
• Stocky
• Adapted to cold weather
• Lived in caves and stone shelters
• Carefully shaped stone tools
HOMINID EVOLUTION
• Homo sapiens: “thinking human”
– Cro-Magnons:
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Fossils found in Europe, Africa, Asia, and Australia
Cranial capacity approximately 1,400 cc
High forehead
Prominent chin
Lack brow ridges
Taller than Neanderthals: 1.6 m or 6 ft
Sophisticated culture
Made a variety of tools: blades, harpoons, scrapers, drills,
fishhooks, needles
• Decorated walls of caves with paintings of animals they
hunted
• Regarded as modern humans
HOMO SAPIEN
HOMO SAPIEN
HOMO SAPIEN
The Road to Modern Humans
• The hominids that have been mentioned so far,
such as Paranthropus and Australopithecus, all
lived millions of years before modern humans
• When did our species, Homo sapiens,
appear?
• Other species in our genus existed before H.
sapiens, and at least two other species in the
genus Homo existed at the same time as
early humans
• As is the case with earlier hominid fossils,
paleontologists still do not completely
understand the history and relationships of
species within our own genus
Hominid Evolution
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The diagram shows fossil hominids
and the time ranges during which
they may have existed
The time ranges are likely to change
as paleontologists gather new data
The question mark after
Sahelanthropus tchadensis
indicates that scientists are not yet
certain that this species is a
hominid
Paleontologists do not yet have
enough information to know how
hominid species are related
It is now clear that hominid
evolution did not proceed by the
simple, straight-line transformation
of one species into another
Current hypotheses about early
stages of human evolution
recognize the incompleteness of
the data
HOMINID EVOLUTION
• Theories of Hominid Evolution
– Two different views still being debated
HOMINID EVOLUTION
Hominid Evolution
The Genus Homo
• About 2.5 million years ago, a new kind of
hominid appeared
• Its fossils show that it resembled modern
humans enough to be classified in the
genus Homo
• Because these fossils were found with
tools made of stone and bone,
researchers called the species
Homohabilis, which means “handy man”
The Genus Homo
• Homo habilis was the first of several species in our
genus to arise in Africa
• About 2 million years ago, a species larger than H.
habilis appeared
• It had a bigger brain and downward-facing nostrils
that resembled those of modern humans
– Today, most researchers call the African fossils of this
species Homo ergaster
• At some point, one or more species in the genus
Homo began migrating out of Africa through what is
now the Middle East
– That species may have been H. ergaster or a closely related
species named Homo erectus
Out of Africa—But Who and When?
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Researchers agree that our genus originated in Africa
But many questions remain
When did hominids first leave Africa?
Did more than one species make the trip?
Which of those species were human ancestors and which were merely relatives?
Fossil data and molecular evidence suggest that hominids left Africa in several
waves as shown in the figure
By a million years ago, migrants from Africa had crossed Asia and reached
China and Java, and populations of H. erectus were living in several places
across Asia
Out of Africa—But Who and When?
• Many researchers have hypothesized that H. erectus was the
first of our genus to leave Africa
• Two recently discovered fossil skulls may offer additional evidence
that H. erectus did leave Africa and migrate long distances
• The skulls, which strongly resemble African H. erectus fossils and
are about 1.75 million years old, were discovered in the country of
Georgia, which is north of Turkey and far from Africa
Out of Africa—But Who and When?
• However, other evidence makes the situation less clear
• Another 1.75-million-year-old skull found in Georgia resembles 1.9
million-year-old Homo habilis skulls from Kenya
• Does this skull indicate that H. habilis left Africa before H.
erectus?
• The scientific jury is still evaluating the evidence
Out of Africa—But Who and When?
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Paleontologists are also unsure
exactly where and when Homo
sapiens arose
One hypothesis, the multiregional model, suggests that
modern humans evolved
independently in several parts of
the world from widely separated
populations of H. erectus
Another hypothesis, the out-ofAfrica model, proposes that
modern humans evolved in Africa
between 200,000 and 150,000
years ago, migrated out to
colonize the world, and replaced
the descendants of earlier hominid
species
Scientific debate, and the search
for more data, continue
Hominid Migration
• Data show that relatives and ancestors of modern humans left Africa
several different times
• But when did early hominids leave Africa, and how far did they
travel?
• By comparing the mitochondrial DNA of human populations
around the world, and by continuing to study the fossil record,
scientists hope to improve our understanding of the complex
history of Homo sapiens
Hominid Migration
Modern Homo sapiens
• The story of modern humans over the past
500,000 years involves two main groups
– The earliest of these species is now called Homo
neanderthalensis, named after the Neander Valley
in Germany where their remains were first found
• Neanderthals, as they are commonly called,
flourished from Europe through western Asia
between about 200,000 and 30,000 years ago
• Evidence from Neanderthal sites in Europe and
the Middle East suggests that they not only
made stone tools but also lived in organized
social groups
Modern Homo sapiens
• The other group is anatomically modern Homo
sapiens—in other words, people whose skeletons
look like those of modern humans
– These H. sapiens, who probably arose in Africa, appeared in
the Middle East around 100,000 years ago
• They joined Neanderthals who had been living in that
region for at least 100,000 years
• As far as anyone can tell, Neanderthals and Homo
sapiens lived side by side in what is now Israel,
Lebanon, Syria, and Turkey for around 50,000 years,
using similar tools and living in remarkably similar
ways
Modern Homo sapiens
• That situation may have changed dramatically around 50,000–
40,000 years ago
• According to one hypothesis, that's when some populations of
H. sapiens seem to have fundamentally changed their way of
life
• They used new technology to make more sophisticated stone
blades, and made elaborately worked tools from bones and
antlers
• They produced spectacular cave paintings
• These Homo sapiens buried their dead with elaborate rituals
• In other words, these people began to behave like modern
humans
• About 40,000 years ago, one such group, known as CroMagnons, appeared in Europe
Modern Homo sapiens
• By 30,000 years ago, Neanderthals had
disappeared from Europe—and from
the Middle East as well
• How and why they disappeared is not
yet known
• But since that time, our species has
been Earth's only hominid