Paleoanthropology

-The study of human origins and evolution

-Paleoanthropologists use two terms that

are easily confused:

Hominoid: refers to the group that

contains the great apes and humans.

Hominid: refers to branches of the

evolutionary tree closest to humans.

There are two main groups of hominids:

Australopithecines, which came first

and are all now extinct

2) Members of the genus Homo, with all

species extinct except one:

Homo sapiens

Major Features of Human Evolution

Brain Size: Hominoids of about 6 mya had

brain volumes of about 400-450 cm3.

-This is close to the volume of a modern day

chimpanzee.

Modern humans have a brain volume of about

1,300 cm3 in size.

This tripling in size is associated with trends such

as the development of complex language and

bipedal locomotion.

2) Jaw Shape: the hominiod ancestors of man

had long prognathic jaws, similar to modern

day gorillas and chimpanzees.

During human evolution, the development of

shorter jawbones resulted in a flatter face with

a more pronounced chin.

Along with the change in jaw shape came a new

pattern of dentition (teeth), and a flattening in

the zygomatic arches around the eyes.

Note the reduction in the angle of the facial

bones, and the flattening of the zygomatic

arches on the sides of the skull.

Also note that the modern human does not

have a sagittal crest.

3) Bipedal posture: Based on skeletal fossils, it is

clear that our ancestors walked on all four limbs

when they were on the ground.

The evolution of bipedal locomotion was linked

to key structural changes in the skeletons of

early hominids.

The pelvis of hominids evolved to be flatter and

Less narrow than those of the apes.

Our feet evolved to have all of the digits facing

forward, aiding in balance for walking.

Evolution of Bipedal Locomotion

4) Reduction in the size difference between males

and females.

In hominoids, the size difference between males

and females is a major feature.

Ex: In gorillas and orangutans, the size difference

is sometimes more than two times.

In humans, the average difference is 1.2 times.

Australopithecines: Early Hominids

and the Origin of Bipedal Posture

Australopithecus africanus: first discovered in

1924 by Raymond Dart.

Discovered in a South African quarry, the fossil

Evidence was clear that A. africanus walked on

two feet, and had human-like hands and teeth.

Southern Ape of Africa

Age: 2-3 million years

In 1974, in the Afar region of Ethiopia, a more

complete skeleton was found.

Nicknamed Lucy, she stood only about 1

meter tall.

The skeleton was sufficiently different from

africanus to be named a new species,

Australopithecus afarensus.

The new species was named for the region in

which it was found.

The age given for A. afarensis is approximately

3.5 to 4.5 million years old.

Fossilized footprints found in Laetoli, Tanzania

confirmed evidence that A. afarensis walked in

a bipedal manner.

Skeletal evidence also indicated that A. afarensis

also led a partially arboreal existence.

Long arms in relation to body size suggest that

afarensis may have led a mixed savannah-

forest existence.

Australopithecus amanensis

Discovered in 1995 by Mary Leakey, A. amanensis

is one of the oldest known australopithecines.

Fossils found include parts of jawbones, arm

and leg bones. A complete skeleton has not yet

been found.

Dentition is marked more ape-like, with larger

canines and a parallel jaw structure.

A fossilized arm joint is more human like than

ape-like.

Australopithecus robustus

A relative of A. afarensis, this species had a very thick and heavy skull.

Robustus was about the same size as

A. afarensis, with a large jaw and teeth well

adapted to chewing.

This species had a sagittal

crest.

Age: 2.1 1.6 mya

Australopithecus bosei

Bosei is very similar to A. robustus, except

that its skull and teeth are larger.

Disagreement exists over the placement of

both A. robustus and A. bosei in the hominid

ancestry.

It is widely held now that both

are relatives of A. africanus.

Age: 2.3 1.1 mya

Some Proposals For The Evolution

Of Hominids

Australopithecus afarensis was the ancestor

both to the later forms of australopithecines and

to Homo.

2) Scientists believe that divergence between

Australopithecus and Homo occurred

between 3.0 and 2.5 million years ago.

3) One branch led to Australopithecus africanus

and then to the more specialized A. robustus and

the variant A. bosei.

4) The other major branch led to Homo habilis,

the earliest member of the genus Homo.

5) Portions of the H. habilis population gave rise

to Homo erectus, and part of the H. erectus

population led to development of Homo sapiens.

6) Modern man emerged as recently as 40,000

years ago.

7) Examination of the trends in evolution indicate

that not all organ systems have evolved at the

same rates.

The concept that different features of an organism

evolve at different rates is known as mosaic evolution.

8) Efficient bipedal movement is a trait that

appeared very early, and it is probably the single

most important development in the emergence

of man.