Chapter 10

Early Hominin Origins and Evolution

Overview

• In northern Tanzania, within East Africa’s Great Rift Valley, lies Olduvai Gorge, one of the most

famous early-human fossil sites ever discovered.

• Olduvai Gorge is located on the eastern branch of the Great Rift Valley, which stretches for

4,000 miles down the east side of Africa.

• Today the Gorge is part of Tanzania

• It was named by a German geologist (Hans Reck), based on his mispronunciation of the

Maasai word for wild sisal. The Maasai word was Oldupai.

• There is an attempt by Tanzanians to revert the name back to Oldupai.

• Olduvai is a steep-sided valley resembling a miniature version of the Grand Canyon.

• The ravine is 300 feet deep and over 25 miles long.

• The semi-arid climate is similar to that seen for the last 2 million years.

• For decades, the husband-and-wife team of Mary and Louis Leakey scoured the barren

hillsides, under an intense equatorial African sun, searching for the remains of our ancestors.

• For almost 30 years, they searched and searched, and found many ancient animal remains and

stone tools, but no bones of the actual tool makers.

• Louis Leakey was the person who concentrated on gathering together the monies, made

most of the public speeches and such.

• Mary Leakey did the majority of the digging and only after her husband past did her role

become more apparent.

• Today, the 3rd generation of Leakeys is digging (Louise), and so there is a Leakey dynasty of

paleoanthropologists.

What Is a Hominin? 1

• The study of human evolution is both interesting and confusing.

• New names, new places abound.

• Arguments between taxonomists flourish.

• I urge you to create a set of tables into which to type the names and dates from the

next several chapters.

• Go here: http://highered.mheducation.com/sites/0078034981/student_view0/index.html

• To identify a hominin fossil, we have to think about the characteristics that are unique to

our lineage.

• Spoken language is unique to humans and has allowed us to use resources in our

environment more effectively

• Humans have sophisticated and complex cultures and also have material cultures that

are preserved in the archaeological record—namely, stone tools.

• Both of these human attributes—language and culture—are underlain by our enormous

brain.

• Humans have small canine teeth that do not hone, or sharpen, against their lower

premolar teeth.

• Only humans move on two legs all of the time (obligate bipedalism).

• Bipedalism has been described as a teetering “on the edge of catastrophe”.

• During normal walking only for about 25% of the time are both feet on the ground.

As we speed up, this percentage decreases.

What Is a Hominin? 2

• Seven anatomies differ between humans and apes, and that are functionally related to our mode of

locomotion.

1. First, the set of the skull on the spine:

• In apes and other quadrupedal mammals, the hole in the bottom of the skull, the foramen

magnum, is positioned toward the back of the skull.

• However, in humans, the skull is relatively well balanced on the spine such that the foramen

magnum is oriented downward.

2. To keep the head balanced above the hips, the spine has to curve in humans and has a characteristic

S-shape (also called lordosis) .In apes and other quadrupedal mammals, the spine is more C-

shaped.

• Most of the differences between a bipedal human and a quadrupedal ape reside below the waist.

3. The pelvis of humans is short and stout, and the hips are positioned on the side of the body, quite

unlike the tall pelvis positioned more toward the back of the ape body.

4. The legs of humans are long, especially relative to the arms, increasing the stride and the efficiency

of our gait. Apes have relatively long arms and short legs, reflecting their arm-hanging and climbing

abilities.

5. To keep the feet and knees in line with the center of mass of the body, the knees of humans slant

inward (valgus knee), giving us a knock-kneed appearance. This angling of the end of the femur is

called a bicondylar angle. Apes lack this.

• Finally, our feet differ.

6. We have an arched foot, which acts as a shock absorber during walking and a spring during running.

Apes lack the longitudinal arch, but they do have a big grasping toe, which helps them climb.

7. The big toe of a bipedal walker is large but is not capable of much grasping.

Obligate Bipedalism vs. Knucklewalking

What Is a Hominin? 3

• Humans and apes have different teeth.

• We have exactly the same number of teeth and the same kinds of teeth, but apes have

very large canines.

• When a gorilla chews, it rubs the back of its canine against the lower premolar tooth,

thus sharpening, or honing, the canine tooth.

• Apes also have a sharp lower premolar with a single cusp and a space between the

incisors and the canine called a diastema.

• Humans, in contrast, have small canine teeth that wear from the top down.

• This is called apical wear.

• Humans also have a large, double-cusped premolar and lack the diastema.

• Why the differences? There appear to be two reasons.

• The first has to do with diet.

• Apes eat plant foods, like leaves and fruit, that require shearing and slicing.

• But, humans and human ancestors instead crush and grind their food and require

differently shaped teeth.

• A second explanation, not emphasized in your book but still important, has to do with

competition for mates.

• Male apes fight with one another for access to resources and mating opportunities.

However, humans tend to pair-bond more than the apes, and selection has not

maintained a large, honing canine tooth in our lineage.

What Is a Hominin? 4

• Tooth enamel and masticatory muscles

• Humans have different internal tooth structure and chewing

musculature.

• Humans have much thicker enamel than chimpanzee teeth have.

• As chimpanzees age, their teeth get worn down. However,

because of the relatively thin enamel, the teeth maintain their

sharpness, which is beneficial for the shearing and slicing

action they use to chew their food.

• Humans, in contrast, do more grinding and crushing.

• This action wears the enamel down more quickly and an

animal without its enamel soon experiences tooth decay,

which can lead to starvation and death.

• Therefore, those individuals with thicker enamel survived,

leading to the thick-enameled tooth we find in humans and

human ancestors.

• Though humans and apes both have the same chewing muscles

(temporalis and masseter), the muscles attach in slightly different

regions of the skull.

• The vertical orientation of our temporalis reflects an adaptation

for crushing food.

• The attachment of the temporalis toward the back of the gorilla

skull causes a slicing motion when it contracts.

Why Did Hominins Evolve? 1

• Charles Darwin’s hunting hypothesis

• Darwin hypothesized that the early evolution of the human lineage took place on the African

continent, and he even proposed a hypothesis for why the hominin lineage evolved from an ape-

like ancestor.

• Humans have 1) very large brains; 2) small nonhoning canine teeth; 3) material culture (now know

that apes make and use tools); and 4) bipedal locomotion.

• He took these four key differences between humans and apes and elegantly packaged them together

in a hypothesis for why the human lineage evolved at all. It is called the hunting hypothesis.

• Darwin postulated that the earliest hominins were different from apes in their diet: They started

to hunt and eat meat.

• To hunt and process meat efficiently, these hominins would have benefited from stone-tool

technology.

• However, to make and use stone tools, hominins would have required a larger brain. But, a

quadruped cannot carry a tool very well; therefore, bipedalism would have evolved as a means

by which the hands could be freed for carrying tools and carcasses. In addition, by using stone

tools, the selection pressure maintaining a large canine tooth would have been reduced, leading

to small canines in hominins. Darwin’s idea is elegant, but it is completely and utterly wrong.

• How do we know? The timing is wrong. This is why fossils are so important. They allow us to

test ideas like Darwin’s hunting hypothesis.

• Upright walking goes back 4–7 million years; stone tools, 3.3 million; and the evidence for

active hunting only dates back to about 2 million years.

• Brains do not really enlarge until 1.8 mya. The timing is off and therefore another

Darwin’s Model

Why Did Hominins Evolve? 2

• Peter Rodman and Henry McHenry’s patchy forest hypothesis

• In the 1980s, they proposed a different explanation of why hominins evolved, called the patchy

forest hypothesis.

• In the late Miocene, Africa was experiencing a cooling and drying period that was causing the

forests to become quite patchy and separated by growing expanses of grasslands.

• Bipedalism may have been energetically more efficient in moving between these food-rich forest

patches, and that this energy economy would have favored upright walking.

• However, recent fossil discoveries are challenging this hypothesis, as some of the earliest bipedal

hominins appear to have resided in more forested habitats.

• Owen Lovejoy’s provisioning hypothesis

• With a shorter interbirth interval, females got access to increased food supplies as they were

provisioned by males who were interested in mating with her. The males carried the food.

• Bipedal males, whose hands were free to carry more high-energy food to their mating partners,

were favored.

• By supplying food to a single interested female, the male can establish a long-term pair-bond

with her. Therefore, he no longer fights with other males over breeding females. Thus, the large

canine tooth is no longer selectively advantageous.

• Lovejoy’s idea is not universally embraced.

• There are ecological problems explaining food sharing and which specific high-quality foods

allowed the shortening of the interbirth interval in early hominins.

• Also, this hypothesis would predict reduced-size dimorphism in early hominins, which is found

in some, but not all, species.

Why Did Hominins Evolve? 3

• Sexual dimorphism

• Many primate species are highly dimorphic. The larger size of males is a result of sexual

competition between males.

• Philip Reno et al. found little sexual dimorphism in early hominin fossils. This suggests males

were cooperative, not competitive.

• Bipedalism: Benefits and costs

• Benefits:

• One can see longer distances as a biped.

• Can carry tools, food and infants.

• Energy efficient, flexible, maneuverable.

• Bipedal walking is an efficient means of covering long distances, and when large game

hunting came into play, further refinements in the locomotor complex may have been

favored.

• More efficient at 2.9 km (chimp walking speed) and 4.5 km (human walking speed)

• One estimate is that early hominin would save 50% of energy as compared to a knuckle-

walker.

• Costs:

• One can see farther, but this means predators can see you.

• Force of gravity is concentrated on very small areas, creating intense pressures on our

vertebrae and feet. This means back problems, fallen arches, and hernias.

• Bipedalism does not allow for very fast running. And if one leg is injured in real trouble.

• Stresses the circulatory system.

What Were the First Hominins? 1

• Sahelanthropus tchadensis

• Central Africa (Toros-Menalla) In 2001, in northern Chad, they found Sahelanthropus tchadensis

• It was dated, using biostratigraphy and, later, using radiometric dating, to between 6 and 7 million

years old. The many other fossils found in the vicinity allowed a reconstruction of a quite forested

environment. No post-cranial bones have been found.

• Fragmentary fossil jaw and teeth resemble an ape.

• The small canine is a hominin trait.

• Lacks the ape trait of the honing complex (shearing canine/premolar arrangement).

• Ape-sized brain and non-protruding face and canine more hominin.

• The braincase is small (350 cm3) and upper canine is reduced (derived).

• It is massively built, with huge brow ridges, a crest on top and large muscle attachments.

• Suggestion of bipedalism from the base of the skull.

• The foramen magnum is the hole in the skull where spinal cord enters brain.

• While debated in Sahelanthropus tchadensis, many suggest a more vertical placement of the

skull (means bipedalism).

• Orrorin tugenensis

• East Africa is where are 2 areas of east Africa that contain significant early hominin fossils

• The first is in the Tugen Hills area of central Ethiopia

• The second is the Middle Awash area of northeastern Ethiopia

• Orrorin tugenensis was found in Tugen Hills of Kenya (East Africa), lived between 7-6 mya.

• Fossils include some dental remains

• Fragmentary leg and arm bones found

• The leg bone has groove evidence for muscle attachment. Indicates bipedalism.

What Were the First Hominins? 2

• Ardipithecus (genus name means ground ape) was found in the Middle Awash, Ethiopia, lived between

5.8 and 4.4 million years ago.

• Two species have been identified:

• Ardipithecus kadabba (species name means basal family ancestor) dates back to 5.8-4.4 mya

• Few fossils, mostly teeth and a few other skeletal fragments.

• Differs from Ardipithecus ramidus as it has more primitive canines.

• Ardipithecus ramidus (species name means root) dates to 4.4 mya species

• If ever there is an example of how fast things change in paleoanthropology this is the one

• The previous edition of your book stated the finds are mainly dental and cranial remains, small

ape-like brain, and indication of bipedalism.

• Major announcement in 2009: There was a reconstruction of A. ramidus that took 15 years.

Skeleton found is surprisingly complete; found close to where “Lucy” lived.

• New data is now available and it adds significantly to the fossil record (Discovering Ardi).

• It is a female, had an estimated cranial capacity of 300-350 cm3, was about 4 feet and weighed

110 pounds.

• The brain was small and ape-like with a cranial capacity of about 300-350 cm3

• The midface protrudes like an ape, the lower face does not.

• The molar teeth are smaller than in apes, but have the thin enamel of apes

• The canines are less ape-like in shape and size

• Ardi appears to have been both bipedal and a climber (arm length are about the same as leg

length)

• Big toe is divergent, unlike in humans, suggesting they climbed on the top of branches.

• Probably did NOT suspend from the branches as do apes.

What Were the First Hominins? 3

• Australopithecus anamensis (from anam (lake) in

Turkana language)

• Found in Kenya and Ethiopia (South Africa), dating

back 4.2 to 3.9 million years ago.

• First found on the shores of Lake Turkana, Ethiopia.

• Most of the evidence is dental, but also some arm and

leg bones

• A few postcranial pieces of fossils were found and

they verify bipedal locomotion, especially the tibia

(See Figure 10.11 for an illustration of this).

• Dental traits more primitive, apelike including a

large canine and a sectorial lower first premolar.

• The back teeth are in parallel rows; the back teeth in

human are more parabolic.

• FYI: Here is a quizlet vocab list that may be of use

• An excellent transition between Ardipithecus and later

hominin species, given its age and mixture of

primitive and derived traits.

• In particular, the teeth become more human-like over

time. Dental arches

What Were the First Hominins? 4

• Australopithecus afarensis (from Afar Triangle, Ethiopia) -- 3.7 to

3.0 mya

• Locations:

• Found by Donald Johanson in the 1970s. First found at found

in Hadar, Ethiopia (East Africa),

• Slightly in time, at Hadar (Ethiopia) and Laetoli (Tanzania) we

find more complete specimens.

• Most of these have been known since the mid-1970s. Several

hundred specimens, representing a minimum of 60 individuals

have been excavated at Laetoli and Hadar.

• The Laetoli footprints

• (discovered in 1978, dating to 3.7-3.5 mya) found in

volcanic ash (A. afarensis); literally thousands of prints

found there of many species

• A 75-foot trail of hominin footprints (2-3 persons)

• The impressions verify bipedalism, but of a different kind.

Their stride, cadence and speed of walking were different.

New version of Lucy (A.

afarensis as more linked to

arboreal adaptation• Debate over how bipedal.

• Apelike tendencies such as long arms, curved finger and toe bones

• The shoulder anatomy is also more apelike

• Two ideas:

• They may simply be retained, but a full obligate biped.

• They may suggest a difference in how bipedal and some time in the trees. Teeth less primitive than A.

anamensis but still more primitive than genus Homo.

What Were the First Hominins? 5

• Australopithecus afarensis (continued)

• Cranial capacity is between 400-500; skull has the look of a small ape; but more apelike in the skull

(small brain and jutting-out face).

• The dentition is less primitive than in earlier hominins.

• Canines intermediate.

• Upper jaw has a diastema between the incisor and the canine.

• The lower premolar is pointed and has 1 cusp.

• Serves to sharpen the upper canine.

• Is intermediate to the 2-cusp (bicuspid) of modern line.

• The most famous of the A. afarensis specimens is Lucy.

• Named after the Beatles song, Lucy in the sky with diamonds (LSD).

• Lucy was quite short (3.5 feet) female with what some call significant sexual dimorphism.

• She was 40% complete, including many key fragments that gave clues to bipedal locomotion.

• At the time of her discovery (along with the Laetoli footprints) the date of first bipedalism was

moved back by at least 1 million years or more.

• New find announced in 2006 of an infant skeleton.

• This is the first infant skeleton found to be older than 100,000 years. (dates to 3-3-3.2 mya)

• Found at Dikaka in NE Ethiopia and nicknamed Selam is estimated age as 3 years.

• “Mixed” pattern of locomotion; skeleton is very similar to that of an adult.

• A second new find dates to 3.6 mya was found at Woranso-Mille, north of Hadar.

• Represents the partial skeleton of a male.

• Confirms that sexual dimorphism was present and that the locomotion pattern was mixture of terrestrial

and ability to move in trees (but not strictly arboreal form of locomotion). Think transitional form.

Hominin Evolution is Bushy 1

• Australopithecus bahrelghazali

• Found in 1993 by Michel Brunet et al. in Chad and dates to 3.6 mya. Unexpected in this locale.

• Found finds, all from teeth and jaw bones.

• Relatively thin enamel, incisor-shaped canines, and three-rooted mandibular premolars.

Like Sahelanthropus tchadensis, has a more vertical lower face.

• Controversial: new species or variant of A afarensis?

• Australopithecus garhi

• In 1999, Tim White and Yohannes Haile-Selassie (the two who discovered Ardipithecus) were working

at a site in the Middle Awash study area called Bouri, which contained 2.5 million-year-old sediments.

• They discovered a very interesting skull. It has a combination of features previously unseen in a

fossil hominin,

• They named it a new species: A. garhi (garhi means surprise in Afar language).

• A. garhi had very large premolar and molar teeth, like an australopithecine.

• It also had relatively large canines and incisors; in other words, all of its teeth were large.

• It has a snouty face, like an ape’s. And the brain is within the range of Australopithecus (450 cc).

• Found nearby the skull was a fragmentary skeleton, which allowed researchers to calculate the

length of the arm relative to the length of the legs.

• Chimpanzees and gorillas have very long arms.

• Humans have very long legs.

• Australopithecus, in general, has an intermediate ratio between modern apes and modern

humans.

• However, A. garhi appears to have longer legs—a more human-like anatomy.

• Additionally, found nearby were antelope bones with cutmarks on them, raising the possibility that A.

garhi was the first stone-tool maker. [Older tool finds negate this now.]

Hominin Evolution is Bushy 2

• Kenyanthropus platyops

• In 2001, Meave Leakey et al. discovered a 3.5 million-year-old skull on the west side of Kenya’s

Lake Turkana.

• Leakey named it Kenyanthropus platyops. Name translates as ‘the flat-faced man from Kenya’.

• Shows a mixture of primitive and derived features.

• Primitive traits: small brain, jutting lower face, and small ear hole.

• Derived traits: small molar teeth, flat face, and tall cheek region.

• Controversial designation challenged by fragmentary and distorted skull.

• Australopithecus deyiremeda

• An upper and lower jaw and some teeth were announced in 2015.

• Teeth have thicker enamel.

• Yohannes Haile-Selassie proposed Australopithecus deyiremeda (in Afar language means ‘close

relative’).

• Dates to 3.5-3.3 mya

• Teeth very small, same as Homo line.

• Controversial.

• Is it a species or subspecies of A. afarensis?

• Which species would be ancestral?

• Summary:

• The big question with all these species and the debate is whether the “lumpers” or “splitters” are

correct.

• While there are likely fewer species than this list indicates, there was greater hominin diversity

than once thought.

OMGosh! IDK!

• In May, 2017 a stunning announcement in the online

journal, Plos ONE: Hominin fossils were found in Europe.

• Actually, the first find was in 1944. A lower jaw was

found in Pyrgos Vassilissis, Greece.

• The more recently discovered find was found in Bulgaria:

an upper premolar.

• They date to approximately 7.2 mya.

• The nickname of this species is “El Graeco”; its

scientific name is Graecopithecus freybergi.

• What is so stunning?

• The researchers are suggesting that the ape-human split

occurred in the eastern Mediterranean and not in

Africa.

• They base their interpretation primarily on a hominin

characteristic noted in the lower molars: partially fused

roots (apes have 2-3 separate roots).

• Critique: Little data to date, and not enough research to

reach this conclusion.

Tool Making

• At one time anthropology defined humans as the only toolmakers.

• The Jane Goodall discovered chimpanzees altering twigs to go

“termite hunting”.

• Many other observations were subsequently noted; most recently

a tribe of chimps makes and uses spears to hunt bush babies.

• When is the earliest archaeological evidence for tool-making?

• Originally, we named this as the Lower Paleolithic Period,

thinking it tool-making began around 2.6 mya and end about

200,000 years ago (ya).

• Two major stone tool industries:

• Oldowan: Hominin tools named for Olduvai Gorge,

Tanzania.

• Tools made by hard hammer percussion (also called

“direct percussion”).

• Assemblages consist mostly of core forms: Choppers &

cores, flakes, and hammerstones.

• Oldowan tools most likely used to process gathered and

scavenged foods, less likely a hunting tradition

• Acheulian (or Acheulean): begins around 1.4 mya

• Date of first tool use is pushed back to 3.39 mya by the find of

bones with cut marks at Dikika, Ethiopia.

• The site is called Lowekwi 3. Most likely use was one of the

australopiths.

• Update: They found the Dikika tools (May 2015).

Dikika tool marks

Dikika stone tools.

The Robust Australopithecines (Paranthropus) 1

• The three species:

• Paranthropus aethiopicus is named for Ethiopia. Most famous is

the ‘Black Skull’ found at Lake Turkana, Kenya.

• Dates to 2.5 mya, has a cranial capacity of 410 cm3, and is

similar to A. afarensis in traits.

• Very robust with primitive cranial traits (such as the anatomy

of the base of the skull).

• Suggested intermediary between A. afarensis and the later

Paranthropus species.

• Paranthropus boisei (2.3-1.2 mya) is found in Omo, Ethiopia and

Olduvai Gorge, Named after Charles Boise (funded the

excavation).

• Formerly named Zinjanthropus boisei.

• Cranial capacity closer to 510-530 cm3 and facial features are

still large and broad.

• Paranthropus robustus is found in South Africa (2.0-1.2 mya),

first by Robert Broom.

• Dentition not as robust as E. African members of this genus.

• Some suggest that Australopithecus robustus is a regional

variant of Australopithecus boisei.

The Robust Australopithecines (Paranthropus) 2

• They went extinct about 1.5 mya.

• They are close relatives, but not our ancestors. Some

suggest a different genus (Paranthropus)

• Physical traits:

• The robust name applies to the teeth

• The front teeth are small, both in size and in

comparison to back teeth

• The premolars and molars were as much as 4X

that of moderns.

• Diet was both soft foods and very hard foods

such as nuts, seeds and hard fruits

• The skull exhibit evidence for heavy chewing:

• Dished-in face with large cheekbones (zygomatic

arch) to accommodate large chewing muscle, the

masseter muscle and the temporalis muscle.Temporalis and masseter muscles (humans)

• The masseter runs through the zygomatic arch and connects to the temporal and zygomatic

bones.

• The temporalis runs from under the jaw, through the zygomatic arch and attaches to the side of

the skull.

• Sagittal crest (bony crest on top) can develop to aid the anchoring of the temporalis muscle in

species with large muscles.

• The rest of their bodies were not that large, average weight was 100 pounds for males, 70 pounds for

females.

• They were bipedal and had small brains.

Australopithecus africanus

• Anatomist Raymond Dart discovered an early hominin form in 1924.

• There are three famous fossils:

• Taung Baby was the first found by Raymond Dart in 1924. It was the first evidence that our origins began

in Africa.

• Little Foot was found in Sterkfontein, South Africa by Ron Clark. Clark found this fossil stashed in a box

and reassembled it.

• Mrs. Ples was found by Robert Broom. She was conclusive evidence that our origins did indeed begin in

Africa. It should also be noted that Mrs. Ples is really Mr. Ples.

• The earliest evidence of hominins in South Africa are from the cave localities of Makapansgat and

Sterkfontein, which are dated to between 2 and 3 million years old. Species:

• These early A. africanus fossils are similar to other australopithecines:

• They have a brain size of about 450 cc (larger than a chimpanzee).

• Small, apically worn canines; and large premolars and molars.

• There are literally hundreds of fossils of this species, and we know quite a bit about their anatomy.

• Based on the lower back, pelvis, knee, and foot, it is clear that these South African australopithecines

walked on two legs; however, their arm and hand bones suggest a continued use of the trees, perhaps

for building nests at night.

• Given the gradual increase in tooth size and the continued adaptations to living on a grassland, it

appears as though A. africanus may have evolved into a robust form in South Africa, completely

independent of the evolution of the robust form in East Africa.

• This would be a wonderful example of convergent evolution, in which features like large molars and

a sagittal crest evolve for dietary reasons.

• The robusts in South Africa (Au. robustus) begin to appear in the fossil record just as A. africanus

begins to vanish, supporting the idea that the latter evolved from the former.

Australopithecus sediba

• Australopithecus sediba (welspring/fountain in local Sotho

language, ~2 mya)

• In 2008 two partial skeletons were discovered at Malapa Cave.

This is a great story and a significant find. In July 2012,

another specimen was found (may be most complete skeleton

every).

• This has been given a new species name as it is a mixture of

australopithecine and Homo features.

• Every single Australopithecus has a C4 isotopic signal,

indicating that it was eating grassland plants and animals. Only

Ardipithecus, and now A. sediba, had a C3 diet

Skull of A. sediba

• Cranial capacity is estimated at 420 cm3, long arms and curved fingers, and more primitive feet.

• Short fingers, brain reorganization.

• Suggests brain reorganization in the frontal lobes may have taken place before expansion of

the brain.

• The pelvis also altered before the brain enlarged; challenges the idea that the changes were

due to the larger brain.

• Many suggest transition species to Homo line.

• The paleoanthropologist, Lee Berger, suggests Australopithecus africanus evolved into

Australopithecus sediba, that evolved into the Homo line.

• Read more here: http://humanorigins.si.edu/evidence/human-fossils/species/australopithecus-

sediba

Australopithecines: Review

• Australopithecus fossils are found only in Africa.

• This group of early hominins evolved about 4 mya and rapidly diversified into many different

species.

• They walked on two legs, occasionally climbed trees, and had relatively small, apically

worn canine teeth.

• They evolved larger and larger premolars and molars, adaptive for grinding tough, fibrous

plant food.

• They lived in woodland and increasingly grassland environments. The earliest species is A.

anamensis, which most likely evolved into Au. afarensis. This latter species is best known

from the famous skeleton Lucy, shown here. But, there may have been other hominins

living at the same time, as evidenced by the Burtele foot (which had a grasping big toe),

and A. platyops, which had a flatter face and smaller teeth (upper right).

• By 3 mya, hominins had spread throughout Africa and begun to live in open grassland

environments in South Africa.

• By 2.5 mya, there were many different species of Australopithecus. The South African.

• Soon after 2 mya, most Australopithecus species had gone extinct and were represented only

by the large-toothed robust forms in East and South Africa.

• However, researchers also began to find fossils of a new kind of creature from around this

time. It had a slightly larger brain than Australopithecus, a smaller face, and smaller teeth:

Homo.