Post on 26-Sep-2015
description
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 firstand 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 hadbrain 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 asA. 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, exceptthat 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 ancestorboth 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.