ANTH 310
Human Origins
LABORATORY #3
EARLY HOMININS: AUSTRALOPITHECINES AND EARLY HOMO
In Preparation for this lab, review the lecture notes, appropriate chapter in the Conroy text, and
pages 282-324 I the Photographic Atlas.
This lab focuses on some of the earliest hominin fossils. The main objectives will be to
observe cranial, dental, and skeletal morphological features in these specimens that will provide
background for assessing the evolutionary history of the human family. The lab format consists
of a number of lab demonstrations specifically designed to illustrate some of the important
cranial, dental, and postcranial variation present in these fossils.
Early Hominins
The earliest specimens, which are considered hominins primarily because of their obvious
adaptations to bipedal locomotion, and because they share dental features (e.g., reduction in the
size of anterior teeth) with later hominins, split from the apes approximately 5-10 mya. Several
different genera and many new species of these early hominins are now known. This lab will
concentrate on some of the most primitive australopithecine species (A. afarensis) as well as
later, robust and gracile varieties and the earliest members of the genus, Homo.
Leaving aside many of the recently discovered fossils (e.g., Ardipithecus ramidus,
Australopithencs anamensis, Australopithencs garhi, A. bahrelghazali, Orrorin tugenensis,
Sahelanthropus tchadensis,and Kenyanthropus platyops), which predate earlier discovered
hominins, the majority of these fossils are classified in the genus, Australopithecus, and are
found at sites located in eastern and southern Africa. Traditionally, this genus has been divided
into a robust and a gracile form. Each is associated with savannah habitats like those found in
Africa, today. The australopithecines disappear from the fossil record shortly after 1 million
years ago.
Australopithecus afarensis
Beginning in the 1970s, a good number of specimens of A. afarensis were discovered at sites
such as Hadar, Ethiopia, and Laetoli, Tanzania. Radiometric dates for these sites range roughly
between 3 and 4 mya.
A. afarensis exhibits a number of primitive as well as derived characters. The most striking
derived character are the adaptations of the pelvis and foot for habitual bipedal locomotion. On
the other hand, A. afarensis retained longer, more curved metatarsals and foot phalanges. Others,
who have undertaken detailed analyses of the foot remains, have argued that A. afarensis was
clearly bipedal and did not use the trees to a great extent (although some have argued that A.
afarensis was more adapted to walking rather than running while others believe that A. afarensis
was still partially adapted to climbing in trees). Others have argued that the long curved
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phalanges are a retention from a common ancestor with the apes. Their bones show that they
were physically very strong. Females were substantially smaller than males, a condition known
as sexual dimorphism. Height varied between about 107 cm (3'6") and 152 cm (5'0"). Body
weight estimates for A. afarensis indicate they weighed between 30 kg and 80 kg.
A. afarensis had an apelike face with a low forehead, a bony ridge over the eyes, a flat nose,
and no chin. They had protruding jaws with large back teeth. Cranial capacity varied from about
375 to 550 cc. The skull is similar to that of a chimpanzee, except for the more humanlike teeth.
The teeth of A. afarensis and all the australopithecines were megadont; i.e., their cheek teeth
were large relative to body size. The canine teeth of A. afarensis are much smaller than those of
modern apes, but larger and more pointed than those of humans, and shape of the jaw is between
the rectangular shape of apes and the parabolic shape of humans.
Some have argued that the specimens from Laetoli and Hadar represent two species while
others maintain that A. afarensis was a highly sexually dimorphic species.
South African Australopithecines
The first australopithecine was discovered by Raymond Dart in South Africa, the Taung
child. Since then, many other specimens have been recovered from South African sites.
Traditionally, the specimens have been placed into two species, A. africanus and A. robustus,
although the latter has been placed in a separate genus (Paranthropus) by some.
Australopithecus africanus specimens are found at fossil sites (e.g., Taung, Sterkfontein) dated
from about 2.3 to 3 million years ago while the A. robustus specimens (e.g., Swartkrans) are
dated from about 1.5 to 2 mya. Because the cranial and postcranial remains of A. africanus
specimens are a bit more delicate than the rugged robust remains of A. robustus, A. africanus is
usually referred to as a ‘gracile’ species while A. robustus is generally referred to as a Arobust’
species although both had average body weights of about 50 kg.
Australopithecus africanus is similar to A. afarensis, and was also bipedal, but body size was
slightly greater. Brain size may also have been slightly larger, ranging between 420 and 500 cc.
This is a little larger than chimp brains (despite a similar body size), but still not advanced in the
areas necessary for speech. The back teeth were a little bigger than in A. afarensis. Although the
teeth and jaws of A. africanus are much larger than those of humans, they are far more similar to
human teeth than to those of apes. The shape of the jaw is now fully parabolic, like that of
humans, and the size of the canine teeth is further reduced compared to A. afarensis.
Australopithecus robustus had a body similar to that of A. africanus, but a larger and more
robust skull and teeth. The massive face is flat or dished, with no forehead and large brow ridges.
It has relatively small front teeth, but massive grinding teeth in a large lower jaw. Most
specimens have sagittal crests. Its diet would have been mostly coarse, tough food that needed a
lot of chewing. The average brain size is about 530 cc.
East African Australopithecines
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There have been no undoubted specimens of A. africanus found in East Africa. However,
hyper-robust species, A. boisei, lived in East Africa between 2.5 mya to just about 1 mya. A.
boisei has been found at several sites in East Africa.. Australopithecus boisei (formerly
Zinjanthropus boisei) is similar to A. robustus of South Africa, but the face and cheek teeth were
even more massive, some molars being up to 2 cm across. The brain size is very similar to A.
robustus, about 530 cc.
The A. robustus/boisei dentition represents the culmination of dental trends first observed in
the Miocene ramamorphs: a reduction of the anterior dentition, enlargement of the cheek teeth
with thick enamel, and thickening of the jaws. The premolars of A. boisei/robustus are referred
to as molariform premolars because of the molar-like form and function of these teeth. The large,
thick-enameled cheek teeth probably provided the surface area for grinding small, tough food
which need little slicing and cutting by the anterior teeth, which are small.
Recently, a robust australopithecine was found in Kenya with a very large face similar to A.
boisei. This specimen, referred to as the ‘black skull’, has been dated to 2.6 mya. It may be an
ancestor of A. robustus/boisei, but it has a baffling mixture of primitive and advanced traits. The
brain size is very small, at 410 cc, and parts of the skull, particularly the posterior portions, are
very primitive, most resembling A. afarensis. Other characteristics, like the massiveness of the
face, jaws and single tooth found, and the largest sagittal crest (a sagittal crest is a bony ridge on
top of the skull to which chewing muscles attach.) in any known hominid, are more reminiscent
of A. boisei. Because it unusual features and early date, this specimen has been placed in a new
species, A. aethiopicus.
Australopithecus aethiopicus, robustus and boisei are all referred to as robust
australopithecines, because their skulls in particular are more heavily built than the gracile
australopithecines.
Estimates of the cranial capacities of the australopithecines range from just under 400 cubic
centimeters (cc.) to more than 500 cc. When body size is taken into consideration, these cranial
capacities are not much more than those of the extant apes. Brain expansion, so characteristic of
out lineage, began with the first appearance of our genus.
Homo habilis/rudolfensis
Living contemporaneously in East Africa (and South Africa) was another hominid species,
Homo habilis. H. habilis, the "handy man", was so called because of evidence of tools found
with its remains. H. habilis existed between 2.4 and 1.5 million years ago. It is very similar to
australopithecines in many ways. The face is still primitive, but it projects less than in
A. africanus. The back teeth are smaller, but still considerably larger than in modern humans.
The average brain size, at 650 cc, is considerably larger than in australopithecines. Brain size
varies between 500 and 800 cc, overlapping the australopithecines at the low end and H. erectus
at the high end. The brain shape is also more humanlike. The bulge of Broca's
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area, essential for speech, is visible in one habilis brain cast, and indicates it was possibly
capable of rudimentary speech. H. habilis is thought to have been about 127 cm (5'0") tall, and
about 45 kg (100 lb) in weight, although females may have been smaller.
Recently, it has been prposed that two species of Homo coexisted 2 million years ago, Homo,
Homo habilis and Homo rudolfensis. Homo habilis was a smaller-brained creature with archaic
postcranial skeleton and H. rudolfensis was larger-brained with a more modem postcranium.
Bipedalism
Because of the changes in the ilium, the center of gravity is different in the pelvic region
between quadrupeds and bipeds. The area of articulation of the sacrum and ilium (auricular
surface) in humans has moved with the ilium until it is closer to the acetabulum, which bring the
weight from the spinal column closer to the femur head. This is a more stable arrangement for a
biped. Abductors and adductors of the femur maintain lateral balance by shifting body weight
more over the sagittal line (midline) of the body. The lateral extension of the ilium and the
lengthening of the femoral neck add power by increasing the lever arm for those muscle.
Comparison of the pelvic (innominate) bones of various Early hominins, modern H. sapiens,
and a living great apes indicates that many of the anatomical features they possess are related to
bipedalism or the lack of bipedalism. The following is a partial list of some of the important
morphological characteristics which are found in the innominate bone of modern hominins:
1. short broad ilium (extends attachment of gluteal muscles)
2. backward extension of iliac crest (moves gluteus maximus)
3. low position of sacral articulation relative to the acetabulum (increases stability in weight
transmission)
4. orientation of sacral articulation relative to whole hip bone
5. sharp angle of sciatic notch produced by bending of ilium onto ischium
6. prominent ischial spine (for ligaments supporting weight)
7. strongly developed anterior inf. iliac spine (for rectus femoris and ilio
psoas, hip flexors)
8. shortened length of the ischium
9. well-marked groove for ilio psoas muscle (this muscle acts to flex and
rotate the hip and supports the hip in extension)
10. orientation and position of the ischial tuberosity in relation to the
acetabulum
The attached diagram will help to locate some of the features mentioned.
The innominate bone of a pongid (e.g., chimp) will possess many features which contrast
those present in hominins.
1. elongated narrow ilium
2. limited iliac crest
3. high position of sacral articulation away from acetabulum
4. less angulated sacrum relative to rest of hip
5. shallow sciatic notch
6. less prominent ischial spine and ant. inf. iliac spine
7. longer ischium (for separate attachment of gluteus maximus) etc.
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Exercise No. 1 Cranial morphology of Early hominins. Using the specimens provided, compare the following cranial features.
Feature
A. afarensis
A. africanus
Cranial size/shape
Face (dimensions,
prognathism, etc.)
Muscle attachments
(sagittal, nuchal crests
etc.)
Forehead
Brow ridge
development/
supraorbital tori
Mandible (size, chin,
etc.)
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A. robustus
Early Homo
Exercise No. 2 Dental morphology of Early hominins. Using the specimens provided, compare the following dental features.
Feature
A. afarensis
A. africanus
Tooth size
Relative size of the
posterior teeth
(premolars and
molars) to anterior
teeth
Canine size/shape
Diastema (location,
size)
Lower first
premolar (P3)
Tooth row shape
Molar (appearance
and cusp patterns)
Other
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A. robustus
Early Homo
Ape
Exercise 3. Postcranial Comparisons. Using specimens of the pelvis, femur, and foot bones of a modern ape, australopithecine, and
modern human, make detailed comparisons of the following traits.
Feature/trait
Ape
Shape of ilium & iliac crest
Greater sciatic notch
Sacro-iliac articulation (extent
& placement reative to
acetabulum)
Acetabulum (size & shape)
Ischial spine
Ant. inf. iliac spine
Ischium length
Femur
Foot bones
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Australopithecine
Modern Human
Exercise 4. Based on your observation in Exercise 3, were the Austalopithecines capable of facultative or
obligatory bipedalism. Explain.
Exercise 5. List some of the major dental and cranial differences between Australopithecus africanus
and Australopithecus robustus.
Australopithecus robustus
Australopithecus africanus
Exercise 6. Make a list of salient differences between the crania of A. robustus with A boisei
Australopithecus robustus
Australopithecus boisei
Exercise 7. What differences are there between KNMER 1470 and KNMER 1813 crania? Do the
differences warrant a separate (or same) species designation? Explain.
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Comparative Anatomy of the Pelvis
Typical Quadruped
(e.g., horse)
Typical Biped
(e.g., human)
Typical Brachiator
(e.g., gibbon)
Ilium
Long & narrow, greater
sciatic notch is very
shallow, forming an
obtuse angle
Short and splayed,
greater sciatic notch is
deeper, less obtuse
Intermediate
Gluteus muscles
Gluteus maximus,
medius, and minimus
are all abductors (draw
leg away from midline
of the body)
Gluteus maximus is an
extensor (see Fig.
below)
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Early Hominids and Their Immediate Ancestors
SPECIES
pre-hominid
apes or
ape-hominid
transitional
species
Sahelanthropus tchadensis
Orrorin tugenensis
7-6?
6.0
Ardipithecus ramidus
5.8 - 4.4
Australopithecus anamensis
4.2 - 3.9
Australopithecus afarensis
4.0 - 2.9
gracile Kenyanthropus platyops
species
Australopithecus bahrelghazalia
early
hominids
TIME RANGE
(millions of years ago)
Australopithecus africanus
Australopithecus garhi
Australopithecus aethiopicus
robust
species Australopithecus robustus
Australopithecus boisei
3.5 - 3.2
3.4 - 3.0
3.3 - 2.3
2.5
2.5
2.0 ? - 1.5
2.0 - 1.2
The species listed above in red are controversial because of relatively limited discoveries
of their fossils and disagreement as to their classification. Those listed in black have
been found at many sites and now are widely accepted. Some researchers refer to the
robust australopithecines as paranthropoids (genus Paranthropus).
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