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Fossil Hominids

The Critters

The Dawn ofMan

Australopithecines

S. tchadensisO. tugenensis

Ar. ram. kadabbaArdipithecus

A. anamensisA. afarensis

K. platyopsA. bahrelghazali

A. africanusA. aethiopicus

A. garhiA. boisei

A. robustus

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Millions of Years Ago

Sahelanthropus tchadensis

• Unveiled July 10, 2002• Toros-Menalla locality, Djurab Desert, northern

Chad, central Africa• Fauna includes aquatic and amphibious animals

alongside gallery forest and savanna fauna– Fish, crocodiles, primates, rodents, elephants, equids,

bovids• Suggests hominid lived close to a lake, but not far

from a sandy desert• Biochronology suggests an age between 6 and 7

million years

Sahelanthropus tchadensisSahelanthropus tchadensis

• Six specimens: nearly complete skull and several fragmentary lower jaws

• Unique mosaic of primitive and derived characters– Primitive: small cranial capacity (320-380 cc), large

central incisor, non-incisiform canines– Derived: Reduced canines, thick molar enamel, nuchal

crest positioning suggesting bipedalism • Skull nicknamed Toumaï

– Local name for a child born perilously close to the start of the dry season (fossils occurred near the earliest evidence of a central African desert)

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Orrorin tugenensis

• Lukeino Formation at Tugen Hills, Kenya• Dated at 6 m.y.a.• Discoverers take great pains to show disimilarity

between Ororrin and the australopithecines, and similarity between Orrorin and Homo– The teeth are relatively small and retain thick enamel– Femur does not rule out bipedalism, but is inconclusive Orrorin

tugenensis

Earliest Hominids

Photo by I.M. Campbell

LT 329: Lothagam

• Dating is set at 5.8 – 5.6 mya• Jaw fragment shows numerous features

reflecting improved power and efficiency in molar grinding– Cannot be distinguished from later Pliocene

australopithecines including A. afarensis(Kramer) and A. ramidus (White)

Ardipithecus ramidus kadabba

• Discovered at Aramis, Ethiopia• Announced in July 2001• Dated at 5.2 – 5.8 million years• Several jaw and bone fragments

– Toe bone resembles A. afarensis, suggesting bipedality

Ardipithecus ramidus kadabbaToe boneToe bone

Mandiblefragment

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Ardipithecus ramidus ramidus

• Discovered at Aramis, Ethiopia• Announced in September 1994• Dated at 4.4 million years• Remains consist of skull and jaw fragments.• Other fossils found with it indicate that it

may have been a forest dweller

Ardipithecus ramidus

Ardipithecus ramidus--2

• Teeth are intermediate between those of earlier apes and A. afarensis, but one baby tooth is very primitive, resembling a chimpanzee– Thin enamel on the molars

• Undescribed remains suggest bipedalism– Foramen magnum positioned forward– Humerus does not appear to be weight bearing– Limestone encased partial skeleton suggests bipedality

New Controversy• For over a century we have expected fossils

to look more and more ape-like as we approach the common ancestor with chimps

• Recently a number of the features that have been assumed to be derived associated with the face and teeth are being re-evaluated– We’re beginning to think that the common

ancestor looked more hominid than ape-like in these features, making it more difficult to tell when we have a very early hominid like Sahelanthropus or Orrorin

Original ModelModern African

Apes

Modern Man

CommonAncestor

6 - 8 million years

More ape-like More hominid-like

New NotionsModern African

Apes

Modern Man

CommonAncestor

6 - 8 million years

More ape-like More hominid-like

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Australopithecus anamensis

• Named in August 1995• Material consists of 9 fossils from Kanapoi

in Kenya and 12 fossils from Allia Bay in Kenya

• Aged between 4.2 and 3.9 million years ago• Mixture of primitive features in the skull,

and advanced features in the body

Australopithecus anamensis

Sectorialpremolars

Australopithecus anamensis--2

• Teeth are a mix of features– Hominid thick enamel on molars– Ape-like sectorial lower first premolar– Relatively large canines

• Tibia suggests bipedality• Humerus is extremely hominid in form

Australopithecus afarensis • Aged between 3.9 and 3.0 million years ago• Apelike face with a low forehead, a bony

ridge over the eyes, a flat nose, and no chin• Cranial capacity from 375 to 500 cc

– Within chimp range, 1/4 - 1/3 modern humans• Pelvis and leg bones far more closely

resemble those of modern man, and leave no doubt that they were bipedal

Australopithecus afarensisLucy: 40% complete skeleton Australopithecus afarensis

Guesstimate based on fragments First nearly complete skull

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Australopithecusafarensis, 4

• Laetoli footprints

• Discovered by Mary Leakey

• Volcanic tuff dated at almost 3.5 million years

• Upright, bipedal locomotion of two or three hominids

Australopithecus afarensis, 5

• Canine teeth 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

• Females were substantially smaller than males, a condition known as sexual dimorphism

Australopithecus afarensis, 6

• Height varied between about 107 cm (3'6") and 152 cm (5'0")

• Finger and toe bones are curved and proportionally longer than in humans, but the hands are similar to humans in most other details

Australopithecus bahrelghazali• Age estimated at 3 - 3.5 mya due to faunal

similarity with Hadar• Single mandibular fragment is generally

similar to Australopithecus afarensis– Incisiform canines, bicuspid first premolar

• Differences from A. afarensis include:– More verticle interior surface of the mandibular

symphysis– Premolars have thin enamel and three roots

(afarensis usually has one or two roots)

Australopithecus bahrelghazali

KT12/H1Photograph by Michel Brunet

Kenyapithecus platyops

• From the site of Lomekwi, western side of Lake Turkana in northern Kenya, named in 2001

• More than 30 skull and dental fragments– Two have been assigned to K. platyops– Other fragments not yet assigned to any genus or species

• Found in deposits reliably dated to between 3.5 million and 3.2 million years ago

• Other mammalian species found at Lomekwi suggest that the site was part of a complex mixture of grassland and wooded habitats– Like other roughly contemporary sites such as Laetoli (Tanzania)

and Hadar (Ethiopia), where remains of A. afarensis have been found

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Kenyapithecus platyops

Holotype KNM-WT 40000 a, left lateral view (markers indicate the plane separating the distorted neurocranium and the well-preserved face). b, Superior view. c, Anterior view. d, Occlusal view of palate. Paratype KNM-WT 38350. e, Lateral view. KNM-WT 40001. f, Lateral view. g, Inferior view. Scale bars: a–c, 3 cm; d–g, 1 cm. (Leakey et al. 2001)

Lieberman on Kenyapithecus platyops

• The fossil resembles chimpanzees and A. anamensis in having a small earhole– It shares many other features of primitive hominins with A.

afarensis and A. anamensis• Cheek teeth with thick enamel• A small brain the size of that of a chimpanzee• Flat nasal margins

• It also has several important derived features– An anterior origin for the root of the cheekbone arch on the upper

jaw– The existence of a flat plane beneath the nose bone (and so the

appearance of a flat face)– A tall cheek region

• Postcanine teeth and brow of the skull are smaller than in A. garhi

More Lieberman

• KNM-WT 40000 has a small cranial capacity but otherwise looks much like the famous KNM-ER 1470 fossil, generally referred to as Homo rudolfensis– These similarities are mostly in the face, and

include the flat plane beneath the nose bone, the tall, vertically oriented cheek region, and the lack of a depression behind the ridge of the brow.

Kenyapithecus platyopsvs. Homo rudolfensis

KNM- WT 40000 KNM- ER 1470

Australopithecus africanus

• A. africanus existed between 3 and 2 million years ago

• Similar to afarensis, bipedal, but slightly larger body

• Cranial capacity ranging between 420 and 500 cc

• Molars are a little bigger than in afarensis

Taung Child Mrs. (?) Ples (Sts 5)

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Australopithecus africanus, 2

• The shape of the jaw is fully parabolic, like humans

• The canine teeth, diastema in upper dentition, and sectorial first lower premolars are further reduced compared to A.afarensis Australopithecus

garhi

Photograph by David Brill

Australopithecus garhi• From Bouri, Middle Awash, Ethiopia, 2.5 m.y.a.• Large teeth

– Cheek teeth at or beyond the robust australopithecine extremes– Large anterior teeth

• Bigger than those of the largest australopithecines• Based on tooth size A. garhi fits with schemes that see gracile

australopithecines as a direct human descendents– Canine-to-premolar/molar size ratios are comparable between A.

garhi, the gracile australopithecines and early Homo

• Long forelimbs and long hindlimbs• Researchers argue that A. garhi represents a direct ancestor

of modern humans that is derived from africanus which is likely derived itself from afarensis

Australopithecus aethiopicus

• Lived between 2.6 and 2.3 million years ago – Known from one major specimen, the Black

Skull, and a lower jaw from Omo – May be an ancestor of robustus and boisei, but

it has a baffling mixture of primitive and advanced traits

• Brain size is small, at 410 cc

Australopithecusaethiopicus

Photograph by Robert I.M. Campbell

Photograph by David Brill

Australopithecus aethiopicus

Photograph by Robert I.M. Campbell

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Australopithecus aethiopicus

Photograph by Robert I.M. Campbell

Australopithecus aethiopicus

• Parts of the skull, particularly the hind portions, are very primitive, most resembling A. afarensis

• The massive face, jaws, and single tooth found, and the largest sagittal crest (the bony ridge on top of the skull to which chewing muscles attach) in any known hominid, are more reminiscent of A. boisei

Australopithecus robustus • Body similar to A. africanus, but larger and

more robust skull, jaws, and teeth• Found primarily in cave deposits estimated at

1½ - 2 mya from Swartkrans and Kromdraai in South Africa

• Massive face is flat or dished, with no forehead and large brow ridges

• Relatively small front teeth, but massive grinding teeth (molars and premolars) in a large lower jaw

Australopithecus robustus

Australopithecus robustus, 3

• Most specimens have sagittal crests• Diet would have been mostly coarse, tough

food that needed a lot of chewing • Average brain size is about 530 cc• Animala bones excavated with A. robustus

skeletons suggest to some workers that the australopithecines may have used bones as digging tools

Australopithecus boisei • A. boisei existed between 2.1 and 1.1

million years ago• Similar to A. robustus, but the face and

cheek teeth even more massive• Cranial capacity averages about 530 cc• Some experts consider A. boisei and A.

robustus to be variants of the same species– Others place them in a separate genus,

Paranthropus

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KNM-ER 406

Photograph by David Brill

Gracile vs. Robust

• Australopithecus afarensis and A. africanusare known as gracile australopithecines, because of their relatively lighter build, especially in the face and teeth – Gracile means slender, and in paleontology is

used as an antonym to robust– Despite this, A. afarensis and A. africanus were

still more dentally robust than modern humans

Gracile vs. Robust, 2

• Australopithecus aethiopicus, A. robustusand A. boisei are known as robust australopithecines, because their skulls are more heavily built– The jaws, cheek teeth, and face are the most

heavily built aspects of these fossil hominids– The canine teeth are quite small in all of these

species

OH 7Discovery of this jaw in 1960 led Louis Leakey to name a new species, Homo habilis, as direct ancestor of man, with Homo erectusrepresenting an extinct side branch

Photograph by John Reader

Homo habilis

• Fossils named “handy man” because of the suggestion of evidence of tools found in contemporary deposits

• Lived between about 2.4 and 1.5 million years ago

• Similar to australopithecines in many ways• Face is primitive, but projects less than in A.

africanus KNM-ER 1813

Photograph by John Reader

Photograph by David Brill

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Homo habilis, 2

• Back teeth are smaller than those of the australopithecines, but still considerably larger than modern humans

• Average cranial capacity, at 650 cc, is 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

Homo habilis, 3

• Brain shape is more humanlike– Bulge of Broca's area, essential for speech, is

visible in one H. habilis brain cast, indicating it may have been capable of rudimentary speech

• H. habilis was about 127 cm (5'0") tall, and about 45 kg (100 lb) in weight, although females may have been smaller

Homo habilis, 4

• Habilis has been a controversial species– Some scientists have not accepted it, believing

that all H. habilis specimens should be assigned to either the australopithecines or Homo erectus

– Many now believe that Homo habilis combines specimens from two or three different species

• Homo habilis• Homo rudolfensis• Homo ergaster

KNM-ER 1470Homo rudolfensis

Photographs by David Brill

Homo rudolfensis• The species designation of Homo rudolfensis is much

debated– Is it a separate species– Is it an australopithecine rather than a homonine

• One of the main problems with H. rudolfensis species is that there are no postcranial remains– Large brains in conjunction with megadont postcanines– Some researchers see the larger brain and tooth size as indicative

of allometric changes due to increased body size--rudolfensis and habilis are the same, with the former the males and the later the females

– Some see rudolfensis as the ancestor of habilis with a decrease in brain size occurring

– Others see the two on completely different evolutionary lines

KNM-ER 992Homo ergaster

Photograph by Robert I.M. Campbell

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Homo ergaster

• Homo ergaster is one of the more problematic of species designations

• Each researcher that sees ergaster as valid sees different specimens as belonging or not belonging

• Most researchers see too little difference between ergaster and erectus to form the basis of a species

• As a general rule of thumb, one can consider most attributed ergaster specimens to be early erectusgeographically confined to Africa

KNM-WT 15000

Photographs by David Brill

Homo erectusfrom Zhoukoudian

Weidenreich Tattersall and Sawyer

Photographs by David Brill

Homo erectus

• Wolpoff claims that H. erectus is an invalid taxon, though few accept this interpretation at this point in time

• Others believe the material attributed to erectus should be split into several different taxons– Asian and later African material remaining as H.

erectus--not contributing to modern humans– Early African material as H. ergaster– European material as H. heidelbergensis

KNM-ER 3733

Photographs by David Brill

Homo erectus

• An increase in brain size to approximately 900 cc• Reduction in postcanine dentition and a decrease

in jaw size• Vertical shortening of the face. • Shortening arm bones, especially forearms to very

modern limb proportions– Postcranial proportions are very similar to tropically

adapted modern humans• Development of a more barrel-shaped chest• The formation of an external nose• Modern human size in terms of height

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Homo antecessor• Approximate brain size of 1000 cc• Marked double-arched browridge

– like later Neanderthals and Chinese H. erectus• Canine fossa but no expanded maxilla

– May be due to the individual's young age since others (ATD 6-58) have an expanded maxilla

• Sharp nasal margin• Shallow maxillary notch• Reduced mandibular corpus thickness when compared to

H. ergaster or early H. erectus• Small postcanines that resemble those of the habilines• M3 reduced relative to M1• Moderate taurodontism

– Characteristic of H. erectus and H. heidelbergensis)• Large I2 dimensions that resemble H. heidelbergensis

Gran Dolina Material Homo antecessor

Photograph by Javier Trueba

Homo antecessor• An important feature that was discovered when the remains

were examined were cut marks that were present on most of the material– 12 parallel cut marks on a temporal fragment where the

sternocleidomastoid muscle attaches– Cut marks on two foot phalanges where the flexor muscle lies

• Dismemberment was the likely goal• Faunal material shows the same cut marks as the hominid

remains– Very few carnivore tooth marks indicates that hominids were

mainly responsible for processing the bones• This is the earliest well-documented case of cannibalism in

a hominid population, and this information is important for deciphering the behavior of early hominids

Homo heidelbergensisfrom Arago

Photographs by David Brill

Homo heidlebergensis

• An increase in brain size to approximately 1200cc• A shift in the widest part of the brain case from

the cranial base to the parietal regions• The rear of the cranial vault becomes more

vertical• A gradual reduction in cranial robusticity• A decline in postcranial robusticity• A tendency for a shift from shorter more robust

stature to taller, leaner bodies

Mauer 1Homo heidlebergensis

• 1907 Mauer sand pits in Germany• Validated Schoetensack's

conviction that Pleistocene human remains would be found in the quarry– Associated with rhino, bear, elephant,

bison, deer, and horse• Schoetensack (1908) named a new

species of hominid, Homo heidelbergensis– New species not justified by

describing unique anatomical features of the species

– Lack of older or other specimens kept heidelbergensis from being accepted

Photograph by John Reader

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Homo heidelbergensis Homo neanderthalensisNeanderthal 1

Photograph by Rheinisches Landesmuseum Bonn

Homo neanderthalensisLa Chapelle-aux-Saints

Photographs by John Reader

Homo neanderthalensisMount Circeo

Photograph by Ministry of Culture, Italy

Homo neanderthalensis • An occipital bun• A suprainiac fossa• Position of the mastoid crest located behind the

external auditory meatus• Position of the juxtamastoid crest located behind

the mastoid crest, and often larger than the mastoid process

• Position of the mastoid process• The supraorbital torus• The supratoral sulcus• A receding frontal• Presence of lambdoidal flattening

Inner Ear Morphology

• Another trait that is being looked at currently as a way of distinguishing Neanderthals in the inner ear morphology

• Researchers are trying to determine if the Neanderthals had a unique inner ear morphology that can be used

• When comparing the values of S/I, humans generally have a value close to 1, chimpanzees have values greater than 1, and Neanderthals have values less than 1

Drawings by C. David Kreger

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References

• LEAKEY, MEAVE G., FRED SPOOR, FRANK H. BROWN, PATRICK N. GATHOGO, CHRISTOPHER KIARIE, LOUISE N. LEAKEY & IAN MCDOUGALL (2001) New hominin genus from eastern Africa shows diverse middle Pliocene lineages. Nature 410, 433 – 440.

• LIEBERMAN, DANIEL E. (2001) Another face in our family tree Nature 410, 419 – 420.

• Kreger, C. David (2001) A look at modern human origins. http://www.modernhumanorigins.com/

Possible evolutionary relationships of the hominids

• The five major genera, with Kenyanthropus in red, Homo in blue, Paranthropus in green, Australopithecus in black and Ardipithecus in yellow– Question marks indicate

hypothetical or conjectural relationships; horizontal bars indicate uncertainty in the species' temporal spans

• Lieberman, 2001