Primate and Human Evolution main points

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Primate and Human Evolution main points

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Title: Primate and Human Evolution main points

1
Chapter 19
Primate and Human Evolutionmain points.1.
primates demonstrate a great deal of variation
andincreasing complexity through time.2.
hominids include present day humans and their
extinct ancestors.3. human evolution is very
complex and in constant state of flux due to new
fossil discoveries made frequently.4. most
famous fossil humans are Neanderthals, which were
suddenly succeeded by Cro-Magnons about 30,000
years ago.
2
Who are we?

Who are we?
Where did we come from?
What is the human genealogy?
These are basic questions
that probably everyone at some time or another
has asked themselves

3
Goes Back Farther Than We Thought

Many people enjoy tracing
their own family history as far back as they can,
similarly paleoanthropologists are discovering,
based on recent fossil finds
that the human family tree goes back
much farther than we thought

4
What Are Primates?

Primates are difficult to characterize as an
order
because they lack the strong specializations
found in most other mammalian orders
We can, however, point to several trends
in their evolution that help define primates
and are related to their arboreal,
or tree-dwelling, ancestry

5
Trends in Primates

These include changes in the skeleton
and mode of locomotion,
an increase in brain size,
a shift toward smaller, fewer, and less
specialized teeth,
the evolution of stereoscopic vision
and a grasping hand with opposable thumb
Not all these trends took place in every primate
group,
nor did they evolve at the same rate in each group

6
Classification of Primates

The primate order is divided into two suborders
The prosimians, or lower primates,
include the lemurs, lorises, tarsiers, and tree
shrews,
while the anthropoids, or higher primates,
include monkeys, apes, and humans

7
Prosimians

Prosimians are generally small,
ranging from species the size of a mouse
up to those as large as a house cat
They are arboreal, have five digits
on each hand and foot
with either claws or nails,
and are typically omnivorous
They have large, forwardly directed eyes
specialized for night vision,
hence most are nocturnal

8
Prosimians

As their name implies
pro means "before," and simian means "ape,
prosimians are the oldest primate lineage,
and their fossil record extends back to the
Paleocene
During the Eocene prosimians were
abundant, diversified, and widespread
in North America, Europe, and Asia

9
Prosimians Are Tropical

By the Oligocene, hardly any prosimians
were left in the northern continents
as the once widespread Eocene populations
migrated south to the warmer latitudes
of Africa, Asia, and Southeast Asia
Presently, prosimians are found
only in the tropical regions
of Asia, India, Africa, and Madagascar

10
Anthropoids

Anthropoids evolved from a prosimian lineage
sometime during the Late Eocene,
and by the Oligocene
they were well established
Anthropoids are divided into three superfamilies

11
Classification of Primates

Order Primates
Suborder Prosimii (lower primates) Lemurs,
lorises, tarsiers, tree shrews
Suborder Anthropoidea (Higher primates Monkeys,
apes, humans
Superfamily Cercopithecoidea Macaque, baboon,
proboscis monkey
Superfamily Ceboidea Howler, spider, and
squirrel monkeys
Superfamily Hominoidea Apes, humans
Family Pongidae Chimpanzees, orangutans,
gorillas
Family Hylobatidae Gibbons, siamangs
Family Hominidae Humans

12
Old World Monkey Attributes

Old World monkeys
superfamily Cercopithecoidea
are characterized by close-set,
downward-directed nostrils
like those of apes and humans
grasping hands,
and a nonprehensile tail
They include
the macaque,
baboon,
and proboscis monkey

13
Old World Monkeys Distribution

Present-day Old World monkeys
are distributed in the tropical regions
of Africa and Asia
and are thought to have evolved
from a primitive anthropoid ancestor,
such as Aegyptopithecus,
sometime during the Oligocene

14
New World Monkeys

New World monkeys
superfamily Ceboidea
are found only in Central and South America
They probably evolved from African monkeys
that migrated across the widening Atlantic
sometime during the Early Oligocene,
and they have continued evolving in isolation
to this present day

15
No Contact

No evidence exists of any prosimian
or other primitive primates
in Central or South America
nor of any contact with Old World monkeys
after the initial immigration from Africa
New World monkeys are characterized
by a prehensile tail, flattish face,
and widely separated nostrils
and include the howler, spider, and squirrel
monkeys

16
Hominoids

Hominoids
superfamily Hominoidea
consist of three families
the great apes
family Pongidae
which includes chimpanzees, orangutans, and
gorillas
the lesser apes
family Hylobatidae
which are gibbons and siamangs
and the hominids
family Hominidae
which are humans and their extinct ancestors

17
Hominoid Lineage

The hominoid lineage
diverged from Old World monkeys
sometime before the Miocene,
but exactly when is still being debated
It is generally accepted, however,
that hominoids evolved in Africa,
probably from the ancestral group
that included Aegyptopithecus

18
Climatic Shifts

Recall that beginning in the Late Eocene
the northward movement of the continents
resulted in pronounced climatic shifts
In Africa, Europe, Asia, and elsewhere,
a major cooling trend began,
and the tropical and subtropical rain forests
slowly began to change to a variety of mixed
forests
separated by savannas and open grasslands
as temperatures and rainfall decreased

19
Apes Adapted

As the climate changed,
the primate populations also changed
Prosimians and monkeys became rare,
whereas hominoids diversified
in the newly forming environments
and became abundant
Ape populations became reproductively isolated
from each other within the various forests,
leading to adaptive radiation
and increased diversity among the hominoids

20
Migration of Animals Possible

During the Miocene,
Africa collided with Eurasia,
producing additional changes in the climate,
as well as providing opportunities
for migration of animals
between the two landmasses

21
Hominoid Relationships

Two apelike groups evolved during the Miocene
that ultimately gave rise to present-day
hominoids
Although scientists still disagree
on the early evolutionary relationships among the
hominoids,
fossil evidence and molecular DNA similarities
between modern hominoid families
is providing a clearer picture of the
evolutionary pathways
and relationships among the hominoids

22
One of the Earliest Anthropoids

Skull of Aegyptopithecus zeuxis,

one of the earliest known anthropoids

23
Dryopithecines

The first group, the Dryopithecines,
evolved in Africa during the Miocene
and subsequently spread to Eurasia,
following the collision between the two
continents
The dryopithecines were a varied group of
hominoids
in size,
skeletal features,
and life-style

24
Proconsul

The best-known dryopithecine and perhaps
ancestor of all later hominoids
is Proconsul,
an ape-like fruit-eating animal
that led a quadrupedal arboreal existence,
with limited activity on the ground
The dryopithecines were very abundant
and diverse during the Miocene and Pliocene,
particularly in Africa

25
Sivapithecids

The second group, the Sivapithecids,
evolved in Africa during the Miocene
and then spread throughout Eurasia
The fossil remains of Sivapithecids
consist mostly of jaws, skulls, and isolated
teeth
There are few body or limb bones known,
and thus we know little about their body anatomy

26
Sivapithecids Ate Harder Foods

All sivapithecids had powerful jaws and teeth
with thick enamel and flat chewing surfaces,
suggesting a diet of harder foods such as nuts
Based on various lines of evidence,
the Sivapithecids appear to be the ancestral
stock
from which present-day orangutans evolved

27
Two Lineages

Although many pieces are still missing,
particularly during critical intervals
in the African hominoid fossil record,
molecular DNA as well as fossil evidence
indicates
that the Dryopithecines, African apes, and
hominids form a closely related lineage
The Sivapithecids and orangutans
form a different lineage that did not lead to
humans

28
Hominids

The hominids (family Hominidae)
the primate family that includes present-day
humans
and their extinct ancestors
have a fossil record extending back
to almost 7 million years
Several features distinguish them from other
hominoids
Hominids are bipedal
that is, they have an upright posture,
which is indicated by several modifications in
their skeleton

29
Comparison of Locomotion

Comparison between quadrupedal and bipedal
locomotion
in gorillas and humans

In gorillas the ischium bone is long
and the entire pelvis is tilted toward the
horizontal

30
Comparison of Locomotion

Comparison between quadrupedal and bipedal
locomotion
in gorillas and humans

In humans the ischium bone is much shorter
and the pelvis is vertical

31
Larger Reorganized Brain

In addition, hominids show a trend
toward a large and internally reorganized brain
An increase in brain size and organization
is apparent in comparing the brains of
a New World Monkey

32
Other Distinguishing Features

Other features that distinguish hominids from
other hominoids include
a reduced face
and reduced canine teeth,
omnivorous feeding,
increased manual dexterity,
and the use of sophisticated tools

33
Geologic Age Ranges

The geologic age ranges
for the commonly accepted species of hominids

34
Debates

Remember that although the fossil record
of hominid evolution is not complete,
what does exist is well documented
Furthermore, it is the interpretation of that
fossil record
that precipitates the often vigorous
and sometimes acrimonious debates
concerning our evolutionary history

35
Oldest Hominid

Sahelan-thropus tchadensis,
the oldest known hominid,
nearly 7 million years old,
was discovered in 2002 in Chad

36
Oldest Hominid

Besides being the oldest hominid,
humans and their extinct ancestors,
Sahelanthropus tchadensis shows a mosaic
of primitive and advanced features
that has excited and puzzled paleoanthropologists
The small brain case and most of the teeth
(except the canines) are chimp-like
However, the nose, which is fairly flat,
and the prominent brow ridges
are features only seen, until now,
in the human genus Homo

37
Australopithecines

Australopithecine is a collective term
for all members of the genus Australopithecus
Currently, five species are recognized
A. anamensis,
A. afarensis,
A. africanus,
A. robustus,
and A. boisei

38
Lucy

A reconstruction of Lucys skeleton
by Owen Lovejoy
and his students at Kent State University, Ohio
Lucy is an 3.2-million-year-old
Australopithecus afarensis individual
whose fossil remains were discovered by Donald
Johanson

This recon-struction
illustrates how adaptations in
Lucys hip, leg and foot
allowed a fully bipedal
means of locomotion

39
Lucy
40
Lucys Babyactually 3.3 MY old
View from back, shoulder blades

Fossil of A afarensis from Dikkia, Ethiopia
3 yr old child, found in sandstone- died during
flood?
Actually 100,000 yrs older than Lucy!
Most complete skeleton ever found!

Scientific American Dec 2006
41
Hominid Footprints

Preserved in volcanic ash at Laetoli, Tanzania
Discovered in 1978 by Mary Leakey,
these footprints proved hominids
were bipedal walkers at least 3.5 million years
ago
The footprints of two adults and possibly those
of a child
are clearly visible in this photograph

42
Brain Size of A. afarensis

A. afarensis had a brain size of 380450 cubic
centimeters (cc),
larger than the 300400 cc
of a chimpanzee
but much smaller than that of present-day humans
(1350 cc average)

43
Apelike Features

The skull of A. afarensis retained many apelike
features,
including massive brow ridges
and a forward-jutting jaw,
but its teeth were intermediate
between those of apes and humans
The heavily enameled molars
were probably an adaptation to chewing fruits,
seeds, and roots

44
Landscape with A. afarensis

Re-creation of a Pliocene landscape
showing members of
Australo-pithecus afarensis
gathering and eating
various fruits and seeds

45
Skull of A. africanus

A reconstruction of the skull
of Australopithecus africanus
This skull,
known as that of the Taung Child,
was discovered by Raymond Dart in South Africa in
1924
and marks the beginning of modern
paleoanthropology

46
Not As Well Adapted for Bipedalism

It appears the limbs
of A. africanus may not have been
as well adapted for bipedalism
as those of A. afarensis

47
Robust Species

Both A. afarensis and A. africanus
differ markedly from the so-called robust species
A. boisei (2.61.0 million years ago)
and A. robustus (2.01.2 million years ago)
A. boisei was 1.21.4 m tall
and weighed between 34 and 49 kg
It had a powerful upper body,
a distinctive bony crest on the top of its skull,
a flat face, and the largest molars of any
hominids

48
A. robustus Was a Vegetarian

A. robustus, in contrast,
was somewhat smaller (1.11.3 m tall)
and lighter (3240 kg)
It had a flat face, and the crown of its skull
had an elevated bony crest
that provided additional area
for the attachment of strong jaw muscles
Its broad flat molars indicated
A. robustus was a vegetarian

49
Australopithecus robustus Skull

The skull of Australopithecus robustus
This species had a massive jaw,
powerful chewing muscles,
and large broad flat chewing teeth
apparently used for grinding up coarse plant food

50
Separate Lineage

Most scientists accept the idea
that the robust australopithecines
form a separate lineage
from the other australopithecine
that went extinct 1 million years ago

51
The Human Lineage

Homo habilis
The earliest member of our own genus Homo
is Homo habilis,
which lived 2.5-1.6 million years ago
Its remains were first found at Olduvai Gorge,
but it is also known
from Kenya, Ethiopia, and South Africa
H. habilis evolved from the A. afarensis and A.
africanus lineage
and coexisted with A. africanus
for about 200,000 years

52
Geologic Age Ranges

The geologic age ranges
for the commonly accepted species of hominids

53
Characteristics of Homo habilis

H. habilis had a larger brain (700 cc average)
than its australopithecine ancestors,
but smaller teeth
It was about 1.2-1.3 m tall
and only weighed 32-37 kg

54
Homo Erectus

In contrast to the australopithecines and H.
habilis,
which are unknown outside Africa,
Homo erectus was a widely distributed species,
having migrated from Africa during the
Pleistocene
Specimens have been found
not only in Africa
but also in Europe, India, China ("Peking Man"),
and Indonesia ("Java Man")

55
Survived in Asia Until About 100,000 Years Ago

H. erectus evolved in Africa 1.8 million years
ago
and by 1 million years ago
was present in southeastern and eastern Asia,
where it survived until about 100,000 years ago

56
H. erectus Differed From Modern Humans

Although H. erectus developed regional variations
in form,
the species differed from modern humans in
several ways
Its brain size of 800-1300 cc,
though much larger than that of H. habilis,
was still less than the average for Homo sapiens
(1350 cc)

57
Size Similar to Humans

H. erectus's skull was thick-walled,
its face was massive,
it had prominent brow ridges,
and its teeth were slightly larger than those of
present-day humans
H. erectus was comparable to size to modem
humans,
standing between 1.6 and 1.8 m tall
and weighing between 53 and 63 kg

58
Skull of Homo erectus

A reconstruction of the skull of Homo erectus
a widely distributed species
whose remains have been found
in Africa, Europe, India, China, and Indonesia

59
H. erectus Was a Tool Maker

The archaeological record indicates
that H. erectus was a tool maker
Furthermore, some sites show evidence
that its members used fire and lived in caves,
an advantage for those living
in more northerly climates

60
Homo erectus Using Tools

Re-creation of a Pleistocene setting in Europe
in which members of Homo erectus are
using fire and stone tools

61
The "Out of Africa" View

Currently, a heated debate surrounds the
transition
from H. erectus to our own species, Homo sapiens
Paleoanthropologists are split into two camps
On the one side are those who support
the "out of Africa" view
According to this camp, early modern humans
evolved from a single woman in Africa,
whose offspring then migrated from Africa,
perhaps as recently as 100,000 years ago
and populated Europe and Asia,
driving the earlier hominid populations to
extinction

62
The "Multiregional" View

On the other side are those supporting the
"multiregional" view
According to this hypothesis,
early modern humans did not have an isolated
origin in Africa,
but rather established separate populations
throughout Eurasia
Occasional contact and interbreeding
between these populations enabled our species to
maintain its overall cohesiveness,
while still preserving the regional differences
in people we see today

63
Homo sapiens Evolved From H. erectus

Regardless of which theory turns out to be
correct,
our species, H. sapiens
most certainly evolved from H. erectus

64
Neaderthals

Perhaps the most famous of all fossil humans are
the Neanderthals,
who inhabited Europe and the Near East
from about 200,000 to 30,000 years ago
Some paleoanthropologists regard the Neanderthals
as a variety or subspecies of our own species
(Homo sapiens neanderthalensis),
whereas others regard them as a separate species
(Homo neanderthalensis)

65
Neanderthal Skull

Reconstructed Neanderthal skull
The Neanderthals were characterized
by prominent heavy brow ridges and weak chin

66
Cold Adapted

The Neanderthal body was
somewhat more massive
and heavily muscled
than ours,
with rather short lower limbs,
much like those
of other cold-adapted people of today

67
Burial Ceremony in a Cave

Archaeological evidence indicates
Neanderthals lived in caves
and participated in ritual burials
as depicted in this painting of a burial ceremony
such as occurred approximately 60,000 years ago
at Shanidar Cave, Iraq

68
Took Care of Their Injured

The remains of Neanderthals
are found chiefly in caves
and hutlike rock shelters,
which also contain a variety
of specialized stone tools and weapons
Furthermore, archaeological evidence indicates
that Neanderthals commonly
took care of their injured and buried their dead,
frequently with such grave items
as tools, food, and perhaps even flowers

69
Cro-Magnons

About 30,000 years ago,
humans closely resembling modern Europeans
moved into the region inhabited
by the Neanderthals and completely replaced them
Cro-Magnons, the name given to
the successors of the Neanderthals in France,
lived from about 35,000 to 10,000 years ago
during this period the development of art and
technology
far exceeded anything the world had seen before

70
Nomadic Hunters

Highly skilled nomadic hunters,
Cro-Magnons followed the herds
in their seasonal migrations
They used a variety of specialized tools
in their hunts, including perhaps the bow and
arrow
They sought refuge in caves and rock shelters
and formed living groups of various sizes

71
Cave Painters

Cro-Magnons were also cave painters
Using paints made from manganese and iron oxides,
Cro-Magnon people painted hundreds of scenes
on the ceilings and walls of caves
in France and Spain,
where many of them are still preserved today

72
Painting From a Cave in France

Cro-Magnons were very skilled cave painters
Painting of a horse
from the cave of Niaux, France

73
Cultural Evolution

With the appearance of Cro-Magnons,
human evolution has become
almost entirely cultural rather than biological
Humans have spread throughout the world
by devising means to deal with a broad range
of environmental conditions
Since the evolution of the Neanderthals
about 200,000 years ago,
humans have gone from a stone culture
to a technology that has allowed us
to visit other planets with space probes
and land astronauts on the Moon

74
Future

It remains to be seen
how we will use this technology in the future
and whether we will continue as a species,
evolve into another species,
or become extinct as many groups have before us

75
Summary

The primates evolved during the Paleocene
Several trends help characterize primate
and differentiate them from other mammalian
orders,
including a change in overall skeletal structure
and mode of locomotion
an increase in brain size
stereoscopic vision
and evolution of a grasping hand with opposable
thumb

76
Summary

The primates are divided into two suborders
the prosimians and the anthropoids
The prosimians are the oldest primate lineage
and include lemurs, lorises, tarsiers, and tree
shrews
The anthropoids include
the New and Old World monkeys,
apes,
and hominids, which are humans
and their extinct ancestors

77
Summary

The oldest known hominid is Sahelanthropus
tchadensis,
dated at nearly 7 million years
then two subspecies of Ardipithecus at 5.8 and
4.4 million years respectively
These early hominids were succeeded by the
australopithecines
a fully bipedal group that evolved in Africa 4.2
million years ago

78
Summary

Currently, five australopithecine species are
known
Australopithecus anamensis, A. afarensis, A.
africanus, A. robustus and A. boisei
The human lineage began
about 2.5 million years ago in Africa
with the evolution of Homo habilis,
which survived as a species
until about 1.6 million years ago
Homo erectus evolved from habilis
about 1.8 million years ago
and was the first hominid to migrate out of Africa

79
Summary

Between 1 and 1.8 million years ago, H. erectus
had spread to Europe, India, China, and Indonesia
H. erectus used fire, made tools, and lived in
caves
Sometime between 200,000 and 100,000 years ago
Homo Sapiens evolved from H. erectus
These early humans may be ancestors of Neaderthals

80
Summary

Neanderthals were not much different
from present-day humans,
only more robust
and with differently shaped skulls
They made specialized tools and weapons,
apparently took care of their injured,
and buried their dead
The Cro-Magnons were the successors
of the Neanderthals
and lived from about 35,000-10,000 years ago

81
Summary

Cro-Magnons were highly skilled nomadic hunters,
formed living groups of various sizes,
and were also skilled cave painters
Modern humans succeeded the Cro-Magnons
about 10,000 years ago
and have spread throughout the world

82
New Hypotheses About Our Ancestry

In this section we examine the various primate
groups,
in particular the origin and evolution of the
hominids,
the group that includes our ancestors
However, we must point out
that new discoveries of fossil hominids,
as well as new techniques for scientific analysis
are leading to new hypotheses about our ancestry

83
Exciting Study

Even as we speak, therefore,
new discoveries may have changed
some of our conclusions
based on what we currently know
Such is the nature of paleoanthropology
and one reason why the study of hominids
is so exciting

84
Variations

In fact, some primates
have retained certain primitive features,
whereas others show all
or most of these trends

85
Classification of Primates

Order Primates
Suborder Prosimii (lower primates) Lemurs,
lorises, tarsiers, tree shrews
Suborder Anthropoidea (Higher primates) Monkeys,
apes, humans
Superfamily Cercopithecoidea Macaque, baboon,
proboscis monkey
Superfamily Ceboidea Howler, spider, and
squirrel monkeys
Superfamily Hominoidea Apes, humans
Family Pongidae Chimpanzees, orangutans,
gorillas
Family Hylobatidae Gibbons, siamangs
Family Hominidae Humans

86
Larger Reorganized Brain

In addition, hominids show a trend
toward a large and internally reorganized brain
An increase in brain size and organization
is apparent in comparing the brains of

a great ape

87
Larger Reorganized Brain

In addition, hominids show a trend
toward a large and internally reorganized brain
An increase in brain size and organization
is apparent in comparing the brains of

a present-day human

88
Ring-Tailed Lemur

Ring-Tailed Lemur are also prosimians

89
New World Monkey

New World Monkeys constitute a superfamily
belonging to the suborder Anthropoidea
(anthropoids)

90
Old Word Monkey

Another superfamily of the anthropoids
the Old World monkeys

91
Chimpanzee

Chimpanzees

92
Early History of Anthropoids

Much of our knowledge about
the early evolutionary history of anthropoids
comes from fossils found in the Fayum district,
a small desert area southwest of Cairo, Egypt
During the Late Eocene and Oligocene,
this region of Africa was a lush, tropical rain
forest
that supported a diverse and abundant fauna and
flora
Within this forest lived many different
arboreal anthropoids as well as various prosimians

93
Thousands of Fossil Specimens

In fact, several thousand fossil specimens
representing more than 20 species of primates
have been recovered from rocks of this region
One of the earliest anthropoids,
and a possible ancestor of the Old World monkeys,
was Aegyptopithecus,
a small, fruit-eating, arboreal primate
that weighed about 5 kg

94
Response to Climatic Changes

Many anthropologists think
these hominid features evolved in response
to major climatic changes
that began during the Miocene
and continued into the Pliocene
During this time, vast savannas
replaced the African tropical rain forests
where the lower primates
and Old World monkeys had been so abundant

95
Mixed Forests and Grasslands

As the savannas and grasslands
continued to expand,
the hominids made the transition
from true forest dwelling
to life to an environment
of mixed forests and grasslands

96
No Clear Consensus

At present, no clear consensus exists
on the evolutionary history of the hominid
lineage
This is due in part
to the incomplete fossil record of hominids
as well as new discoveries,
and also because some species
are known only from partial specimens
or fragments of bone
Because of this, scientists even disagree
on the total number of hominid species

97
Some Current Theories

A complete discussion
of all the proposed hominid species
and the various competing schemes of hominid
evolution
is beyond the scope of this course
However, we will discuss the generally accepted
taxa
and present some of the current theories
of hominid evolution

98
Evolutionary Scheme

Many paleontologists accept
the evolutionary scheme in which
A. anamensis,
the oldest known australopithecine,
is ancestral to A. afarensis,
who in turn is ancestral to A. africanus
and the genus Homo,
as well as the side branch of australopithecines
represented by A. robustus and A. boisei

99
Oldest Known Australopithecine

The oldest known australopithecine
is Australopithecus anamensis
and was discovered at Kanapoi,
a site near Lake Turkana, Kenya,
by Meave Leakey
of the National Museums of Kenya
and her colleagues

100
Similar Yet More Primitive

A. anamensis, a 4.2-million-year-old bipedal
species,
has many features in common
with its younger relative, A. afarensis,
yet is more primitive in other characteristics,
such as its teeth and skull
A. anamensis
is estimated to have been
between 1.3 and 1.5 m tall
and weighed between 33 and 50 kg

101
Australopithecus afarensis

Australopithecus afarensis,
which lived 3.93.0 million years ago,
was fully bipedal
and exhibited great variability in size and
weight
Members of this species ranged
from just over 1 m to about 1.5 m tall
and weighed between 29 and 45 kg

102
Hominid Footprints

Most scientists think the footprints
were made by Australopithecus afarensis
whose fossils are found at Laetoli

103
A. africanus Lived 3.02.3 mya

A. afarensis was succeeded by
Australopithecus africanus,
which lived 3.02.3 million years ago
The differences between the two species are
relatively minor
They were both about the same size and weight,
but A. africanus had a flatter face
and somewhat larger brain

104
Specimens Found in Neander Valley

In any case, their name comes
from the first specimens found in 1856
in the Neander Valley near Düsseldorf, Germany

105
Neanderthals Difference

The most notable difference between Neanderthals
and present-day humans is in the skull
Neanderthal skulls were long and low
with heavy brow ridges, a projecting mouth,
and a weak, receding chin
Their brain was slightly larger on average
than our own, and somewhat differently shaped

106
First Humans in Cold Climates

Given the specimens from more than 100 sites,
we now know Neanderthals
were not much different from us,
only more robust
Europe's Neanderthals were the first humans
to move into truly cold climates,
enduring miserably long winters and short summers
as they pushed north into tundra country

107
Understanding in Flux

So where does this leave us, evolutionarily
speaking?
At a very exciting time as we seek to unravel the
history of our species
Our understanding of our genealogy
is presently in flux,
and each new fossil hominid find
sheds more light on our ancestry

108
Human Evolution

Apparently human evolution
is just like that of other groups
Just as with non-hominid predecessors,
our ancestors followed an uncertain path
As new species evolved,
they filled ecologic niches
and either gave rise to descendants
better adapted to the changing environment
or became extinct

109
Continuing Discoveries Change Our Ideas

As recently as 2000,
the earliest fossil evidence of hominids
was from 4.4-million-year-old rocks in eastern
Africa
Since then, as just noted, discoveries have
pushed
that age back to almost 7 million years

110
Anthropoid Superfamilies

Anthropoids are divided into three superfamilies
Old World monkeys,
New World monkeys,
and hominoids

111
Next Oldest Hominid

The next oldest hominid is Orrorin tugenensis,
whose fossils have been dated at six million
years
and consist of bits of jaw, isolated teeth,
finger, arm, and partial upper leg bones
At this time, debate continues
as to exactly where Orrorin tugenensis fits in
the hominid lineage

112
Ardipithecus ramidus

Sometime between 5.8 and 5.2 million years ago,
another hominid was present in eastern Africa
Ardipithecus ramidus kadabba is older
than its 4.4 million year old relative
Ardipithecus ramidus ramidus
Ardipithecus ramidus kadabba is very similar
in most features to Ardipithecus ramidus ramidus
but in certain features of its teeth
is more apelike than its younger relative

113
Geologic Age Ranges

The geologic age ranges
for the commonly accepted species of hominids

114
Bushy Model of Human Evolution

For instance, paleoanthropologists now think
that human evolution branched many times
rather than evolving in a somewhat straight line
leading to modern humans
According to this bushy model
of human evolution,
such key traits as
upright walking,
manual dexterity
and a large brain
evolved more than once,
and produced many evolutionary dead-ends

115
When Humans and Chimpanzees Diverged

Presently, most paleoanthropologists accept
that the human-chimpanzee stock separated
from gorillas about 8 million years ago
and humans separated from chimpanzees
about 5 million years ago
Thus Sahelanthropus tchadensis is
at or near the point in time
when humans and chimpanzees diverged

116
Oldest Known Hominid

Discovered in northern Chad's Djurab Desert
in July, 2002,
the nearly 7-million-year-old skull
and dental remains of Sahelanthropus tchadensis
make it the oldest known hominid yet unearthed
and very close to the time
when humans diverged
from our closest-living relative, the chimpanzee

117
Habitual Bipedal Walkers

Although many paleoanthropologists think
both Orrorin tugenensis and Ardipithecus ramidus
kadabba
were habitual bipedal walkers
and thus on a direct evolutionary line to humans,
others are not as impressed with the fossil
evidence
and are reserving judgment
Until more fossil evidence is found and analyzed,
any single scheme of hominid evolution presented
here would be premature

118
Global Climatic Cycles in Geologic Time
from L E Waite (2002), modified from Fischer
(1984)
119
Temperature change last 2000 years
http//dels.nas.edu/dels/rpt_briefs/Surface_Temps_
final.pdf
120
Temperature change _at_ different time scales
Glacial and Interglacial Periods
http//dels.nas.edu/basc/Climate-LOW.pdf
121
Leg Bones and Feet Needed