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Hominid !Evolution:On The Origin of

Humans

What is a Hominid?

•  The term “hominid” is also used in the more restricted sense as “hominins”

•  Humans and relatives of humans closer than chimpanzees

•  Bipedal

•  Modern man is the only member of this group alive today

Hominid Sites •  Earliest fossil hominid sites are in Africa

•  They now span the latest Miocene to the early Pleistocene from about 6-7 mya to about 1.6 mya

• The major groups of sites are:

1.  Ethiopia = Middle Awash valley & Hadar (Australopithecus afarensis)

2.  Kenya = Lake Turkana

3.  Tanzania = Olduvai Gorge

4.  South Africa = various sites in limestone caverns centered around Sterkfontein

What Makes A Hominid? - Bipedalism

•  Primary feature distinguishing hominids from other hominoids is walking erect on two legs – erect bipedalism

•  Adaptations for bipedalism in the partial skeleton of “Lucy,” an australopithecine ( 3.2 mya) clearly seen in the hip, spine and leg bones

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Why did bipedalism become the primary adaptation of hominids?

Climate Change resulting in forest habitat being replaced by grasslands.

Advantages of Bipedalism

1. Carrying behavior 2. Reduction of overall heat stress - facilitates

heat loss through convection by exposing body to air currents, only humans have sweat glands that produce moisture to cool body

3. Most energy efficient way to travel long

distances 4. Allows for better vision in open environments &

defensive action against predators by freeing hands to throw objects

Evidence for Early Bipedalism

•  The record of bipedalism is most graphically preserved in the fossilized footprints at Laetoli, Tanzania, 3.6 mya

•  Tracks of 2 individuals were uncovered in volcanic ash by Mary Leakey (1978-79)

•  Footprints were left by 2 australopithecines in damp volcanic ash of Laetoli

• Notice how close the tracks are!

Laetoli Footprints •  Laetoli footprints

clearly show that the creatures who made them were fully bipedal

•  Big toe hardly diverges from the rest of the foot, unlike in apes

•  Gait = “heel-strike” followed by “toe-off” – the way modern humans walk

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•  2 early hominids walk bipedally across an open ash field produced by an erupting volcano.

•  Rain wet the volcanic ash & footprints filled up with more ash, and were thus preserved.

•  Footprints reveal that our ancestors walked upright with a gait very similar to our own.

Laetoli Reconstruction First Adaptive Radiation

n  7-6 mya in the late Miocene, potential last common ancestors between humans and apes

1. Sahelanthropus tchadensis

7-6 mya in Chad (North Central Africa) 2. Orrorin tungenensis

6 mya in Kenya (East Africa)

Note: These organisms were forest adapted.

1. Sahelanthropus tchadensis

•  Discovered in Chad (7-6 mya)

•  Most complete cranium from this time period

•  Mosaic of ape & human-like features, but at the “ape grade” of evolution:

•  Cranial capacity (320-380 cc)

•  U-shaped upper jaw

•  Very wide distance between the orbits

•  Large, thick continuous brow ridge

•  Human-like flat face

•  Human-like dentition

2. Orrorin tungenensis

•  Fossils from Tugen Hills in Kenya have been dated to about 6 mya

•  Earliest Evidence for Walking on Two Legs?

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Orrorin tungenensis (cont.)

•  Fossils Include: upper portion of a femur, lower portion of the humerus, some lower jaw fragments, & teeth

•  Arm bone: virtually identical to that of a chimpanzee

•  Femur: more human-like, most important for showing adaptations for walking on 2 legs

•  Was Orrorin a direct human ancestor, or a common ancestor of chimps and humans?

Second Adaptive Radiation

n  5-4 mya in early Pliocene, first true hominids

1. Ardipithecus ramidus

5.5-4.5 mya in Ethiopia (East Africa) 2. Australopithecus anamensis

4.2-3.9 mya in Kenya (East Africa)

Note: These organisms were forest adapted and fully bipedal.

1. Ardipithecus ramidus

Earliest True Hominid or Last Common Ancestor?

LAST COMMON ANCESTOR OF CHIMPS & HUMANS MOST LIKELY HAD A MIX OF FEATURES: SOME RETAINED IN CHIMPS, OTHERS RETAINED IN

HUMANS!

Ardipithecus ramidus (cont.)

n  Between 4.5 and 5.5 mya from the Middle Awash valley site in Ethiopia

n  Fossil Remains very fragmentary:

limb bones, toe bones, jaws & teeth

n  Straight toe bones suggest it may

have been bipedal n  A mosaic of features seen in later

hominids & modern chimpanzees

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2. Australopithecus anamensis

n  Lake Turkana Region of Kenya

n  4.2-3.9 mya n  Probably walked

upright n  Teeth enamel thicker

than Ardipithecus ramidus, so diet included hard foods

•  Fossil Remains very fragmentary

•  Those shown here include:

• Jawbone

• part of the front of the face

• parts of an arm bone (radius)

• fragments of a lower leg bone (tibia)

Australopithecus anamensis (cont.)

Third Adaptive Radiation

n  4-3 mya in middle Pliocene, many hominids 1. Australopithecus afarensis (“Lucy”)

4-3 mya in East Africa 2. Australopithecus africanus

4-2.5 mya in South Africa 3. Kenyanthropus platyops

3.5-3.2 mya in Kenya

Note: These organisms lived in open woodlands & along wooded streams in the savannas, ate fruits and soft foods, maybe had a tool-culture like modern chimps

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1. Australopithecus afarensis

n  4-3 mya in East Africa n  Pelvis & leg bones resemble

modern humans n  Sexual dimorphism (males

larger with sagittal crest) n  Tree climbers (curved fingers &

toes) Ape-like Features: n  Small brain case (430 cc.) n  Prognathic (jutting out) face n  U-shaped palate (v. parabolic

shape)

Australopithecus afarensis

A. afarensis Skeleton - Lucy 2. Australopithecus africanus

n  4-2.5 mya in Transvaal region of South Africa

n  1924: 1st

Australopithicine to be described by Raymond Dart!

n  Globular cranium,

slightly higher ratio of brain to body size than A. afarensis

n  Face less prognathic

than A. afarensis n  Proportions of arm to leg

lengths may be more ape-like than A. afarensis

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Australopithecus africanus

Taung Child

Most complete A. africanus

skull

best known A. africanus

cranium (front & lateral views)

Australopithecus africanus

A. afarensis

Australopithecus africanus

Australopithecus afarensis

A. afarensis verses A. africanus

3. Kenyanthropus platyops

n  3.5-3.2 mya: found in 2001 west of Lake Turkana in Kenya

n  Ape-like features: small ear canal, small

brain case n  Human-like features: flat face, small molars n  Importance: flat face appeared early in

evolution, alongside the range of other facial forms. Evidence that evolution is not linear or progressive.

Kenyanthropus platyops

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Fourth Adaptive Radiation

n  3-1 mya in late Pliocene, more “robust” hominids 1. Paranthropus boisei

2.2-1.2 mya in East Africa

2. Paranthropus robustus 2-1 mya in South Africa

3. Australopithecus garhi

3-2 mya in East Africa

Note: Lived in open dry woodlands & savannas. The robust species are famous for eating hard-to- chew food, like seeds, nuts, and roots. May have used tools to dig for roots in dry seasons.

1. Paranthropus boisei

n  2.2-1.2 mya in East Africa: Ethiopia, Kenya, Tanzania

n  Largest teeth found in any

hominid! n  Referred to as “hyper-robust” due

to massive molars and premolars n  Skull: broad, short face with

flaring cheek bones, relatively small brain, pronounced sagittal crest in males

n  Skull and dental features are

adaptations for heavy chewing!

Paranthropus boisei (KNM-ER 406) Paranthropus boisei (KNM-ER 406)

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2. Paranthropus robustus

n  2-1 mya in South Africa n  Short, broad face with deep

zygomatic arches (cheek bones). Larger individuals have sagittal crests.

n  Large molars covered with thick

enamel n  Wear patterns on teeth: herbivorous

diet of hard resistant foods such as seeds, nuts, roots

n  Lived in grasslands near rivers and

wetlands

Paranthropus robustus

3. Australopithecus garhi

n  3-2 mya in East Africa: spotty fossil record, cranial & dental remains found in 1999 in Bouri, Ethiopia

n  Bones of antelopes, horses, and other animals with cut marks made by stone tools: butchering animals & smashing bones for marrow. First meat eaters?

n  Molars too large to be early Homo genus

n  Ape-like long lower arm, human-like upper arm & leg

n  Mixed traits: classified as a new species, maybe ancestor of early Homo genus

Australopithecus garhi

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One surprise in the A. garhi skull was enormous back teeth, instead of smaller ones seen in later Homo species

Australopithecus garhi

EARLIEST BUTCHERS:

•  Signs that hominids scraped & smashed animal bones, like this antelope tibia, 2.5 mya

•  Earliest documented percussion marks made by hominids, presumably extracting fatty marrow from these bones

Australopithecus garhi

Rise of the Genus Homo

n  Homo habilis – “Handy Man” n  Homo erectus – or Homo ergaster in Africa n  Homo heidelbergensis – “Archaic Homo sapiens” n  Homo sapiens neanderthalensis - Neanderthal n  Homo sapiens sapiens – Modern Man

Homo habilis

n  Slightly larger braincase and smaller face and teeth than Australopithecus

n  Still retains ape-like features of long arms and moderately prognathic face

n  Average height = 3’4’’ to 4’5’’

n  Average weight = 70 lbs.

2.4 – 1.4 MYA

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Homo habilis

n  Thick tooth enamel suggests they had an omnivorous diet, but were capable of eating fairly tough foods like leaves and woody plants

By this time, the feet of early humans had a modern-type

arch

Homo erectus

n  Modern human-like body proportions indicate adaptations for living exclusively on the ground

n  Expanded braincase relative to the size of the face

n  Left Africa and spread into Asia n  Longest lived early human relative (9

times longer than we have been around so far)

n  Used fire (warmth, cooking) n  Evidence they cared for the sick and

old (see skull to left) n  Average height = 4’9’’ to 6’1’’ n  Average weight = 88-150 lbs.

1.89 MYA – 143,000 years ago

Homo erectus

Turkana boy fossil

Hand axe – first major innovation in stone tool technology

Homo heidelbergensis

n  Very large brow ridge n  Larger braincase and flatter

face than earlier human ancestors

n  Short, wide bodies adapted to living in colder climates

n  Most likely candidate to have been common ancestor between Neanderthals and modern humans

n  Average height = males 5’9’’, females 5’2’’

n  Average weight = males 136 lbs., females 112 lbs.

700,00 – 200,00 years ago

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Homo heidelbergensis

n  Used wooden spears to routinely hunt large animals

n  Built shelters out of wood and rock

Homo sapiens neanderthalensis

n  Short, stocky bodies and huge noses were adaptations for living in cold environment

n  Larger braincase than modern man n  Sophisticated tools, used shelters, wore

clothing n  First human ancestor to bury their dead

and mark the graves n  Modern humans led to their extinction but

unclear as to exactly how n  Average height = males 5’5’’, females

5’1’’ n  Average weight = males 143 lbs., females

119 lbs.

200,000 – 28,000 years ago

Homo sapiens neanderthalensis

La Ferrassie 1 – Most complete Neanderthal skull ever found

Ornamental jewlery

Homo sapiens sapiens

n  Originated in Africa 200,000 years ago

n  Highly vaulted, thin-walled skull led to more developed frontal lobe of brain

n  Flat forehead and face

n  Less heavily developed jaws and small teeth

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Homo sapiens sapiens Homo sapiens sapiens

Many advancements in art, culture and tool making technology

Map of Hominid Evolution