BIPEDALISM & EARLY HOMININS

Methods for Studying Hominin Evolution

1. comparitive morphology

   1. cranial morphology

   2. dental characteristics

   3. postcranial characteristics

2. fossilization

3. absolute and relative dating

4. endocranial casts and microwear of teeth

5. molecular evolution & DNA analysis

Two types of methods used by Paleoanthropologists

relative dating

absolute (chronometric) dating

Early Hominins: Australopithecines

appeared in africa ~5 million years ago (at least)

from the waist down, fully adapted for bipedalism

from the waist up, somewhat apelike, with intellectual abilities comparable to those of modern-day chimpanzee

forms of austropolithecus

earlier forms preserve a numbr of features that indicate an apelike ancestor

by ~2.5 mya, a new form with larger chewing apparatus and more massive head, while brain size remained stable

Australopithecus

adult stature ~4’ tall

general appearance of an ape-like human

size and outward appearance of brain suggest an intelligence similar to a modern bonobo, chimpanzee, or gorilla

Paranthropus (aka: robust austrolopithecines)

• shared most of the traits of genus Australopithecus from neck down

• bones were thick with prominent markings where muscles attaches

• skull was thicker and larger with a slightly larger cranial capacity

• skull possessed an ape-like sagittal crest

• genus Paranthropus

Species of Australopithecus

gracile species - location

• A. afarensis - ethiopia & tanzania

• A. africanus - south africa

• A. anamensis - Kenya

Species of Paranthropus

Robust species - location

• paranthropus aethiopicus - Kenya

• P. boisei - Kenya

• P. robustus - south africa

How do we know australopithecines walked upright?

• bowl-shaped pelvis with broad ilium

• angled hip and knee joints

• foramen magnum below skull

• s-shaped vertebral column (2 curves)

• enlarged big tow in line with others

• footprints (at Laetoli, Kenya) 3.7 mya

footprints at laetoli, kenya

• discovered by Mary Leakey in the late 1970s

• 54 hominid footprints pointing north two parallel tracks 2 individuals

• preserved under layers of volcanic ash and sediments that also held footprints of other animals

• radioactive dating: 3.7 mya

bipedalism: drawbacks

• makes an animal more visible to predators

• exposes the soft underbelly

• interfered w/ability to change direction instantly while running

• quadrupedal chimpanzees and baboons are around 30% faster than bipeds

• frequency lower back problems, hernias, hemorrhoids, and other circulatory problems

• consequences of a serious leg or foot injury seriously hinders a biped (easy meal for a carnivore)

reasons for (or outcomes of…) bipedalism

• a way to cope with heat stress

• allowed them to gather food and transport it to a safe place for eating

• mothers were able to carry their infants safely

• they could reach food on trees too flimsy to climb

• allowed them to travel far without tiring

• food and water were easier to spot

• more likely to spot predators before they got too close

• hands freed from locomotion provided protection by allowing them to throw objects at attackers

Ardipithecus ramidus

• estimated age: 5.8 to 4.4 million years

• date of initial discoveries: 1994-1999

• location: ethiopia

• >20 different specimens have been found with many bones present

• placement of foraman magnum suggests bipedality; limb proportions are ape-like

Australopithecus anamensis

• estimated age: 4 million years

• date of discovery: 1994 (*initally discovered, but not identified, in 1965 by a harvard expedition)

• location: kenya

• fossils include upper and lower jaws, cranial fragments, upper and lower tibia

• range of primitive and advanced morphological features. general similarity between this species and A. ramidus

• both species retaind ape-like crania and dentition, while also having advanced postcrania

Australopithecus afarensis

• estimated age: 4 to 3 million years

• date of discovery: 1970s

• location: ethiopia, tanzania, kenya

• still the best known early hominin species

• evidence for habitual bipedality

• presence of evolutionary trends in dentition and post-crania that suggest it’s on the path to a more modern human form

the “Lucy” skeleton (Australopithecus afarensis)

• estimated age: 3.2 million years

• date of discovery: 1974

• location: ethiopia

• lucy was an adult female for about 25 years

• about 40% of her skeleton was found, and her pelvis, femur, and tibia showed to have been bipedal

• she stood only about 3.5’ tall

“lucy’s daughter (Australopithecus afarensis)

• estimated age: 3.3 million years

• date of discovery: 2000 (publ. 2006)

• location: ethiopia

• near complete remains of a 3 year old girl

• remarkable opportunity to study growth and development in an important extinct human ancestor

• est. brain size 330 cm³

• chimps: by 3 years of age, 90% of brain is formed

• so: relatively slow brain growth in this girl appears to be closer to that of humans

TED: “The Search for Humanity’s Roots”

Paleoanthropologist Zeresenay "Zeray" Alemseged digs in the Ethiopian desert, looking for the earliest signs of humanity. His most exciting find: the 3.3-million-year-old bones of Selam, a 3- year-old hominin child, from the species Australopithecus afarensis.

Australopithecus africanus

• Estimated age: 3 to 2 million years
  • Date of discovery: 1924
  • Location: South Africa
  • Many features of the cranium are more ‘advanced’ than that of earlier A. afarensis: higher brain to body size ratio; teeth and face appear less ‘primitive.’
  • A. africanus is an enigma to paleoanthropology - we are still unsure where A. africanus came from and which species, if any, it led to.
  • To figure out A. africanus would help to clarify an early chapter in our evolutionary history. 34

Paranthropus boisei

• Estimated age: 2.3-1.2 million yrs
• Date of discovery: 1959
• Location: Tanzania, Ethiopia, Kenya
• The cranium has sagittal crests, and
a strikingly broad and robust face.
• The orbits are wider than they are
high and the zygomatic arches
(cheekbones) are flared.

Paranthropus aethiopicus

• Estimated age: 2.5 million years
• Date of discovery: 1985
• Location: Kenya
• A “robust” australopithecine, and not
considered a direct line to humans.
• Latest dating techniques place it
somewhere between A. afarensis and
A. boisei.

Paranthropus robustus

• Estimated age: 2-1 million years
• Date of discovery: 1930s
• Location: South Africa
• This species added significantly to the knowledge of robust australopithecines.
• It has a sagittal crest, large zygomatics (cheek bones) with relatively small front teeth and large back grinding teeth.

Kenyanthropus platyops

• Estimated age: 3.5 million years
• Date of discovery: 1998
• Described in 2001 in the journal Nature as a new genus.
• Location: Lake Turkana, Kenya
• A mixture of primitive and modern traits characterize the two partial skulls found. These traits include a flattened face and small teeth like early Homo

Orrorin tugenensis

• Estimated age: 6 million years
• Date of discovery: 2000
• Published in 2002
• Location: Kenya
• Evidence for this species is made up of > 2 dozen fossils, including a partial femur, bits of a lower jaw, and several teeth.

Sahelanthropus tchadensis

• Estimated age: 6-7 million years
• Date of discovery: 2001
• Published in 2002
• Location: Chad (southern edge of the Sahara Desert)
• At between 6 and 7 million years old, this skull is the earliest known record of the hominid lineage.
• This find, nicknamed 'Toumaï', comes from the crucial yet little- known interval when the hominid line was becoming distinct from that of the Miocene apes

development of human culture

some populations of early hominins began making stone tools to process animals for meat/fat for dig tubers, etc.

the earliest stone tools and evidence of a more diverse diet that included some animal protein/fat date to about 3 mya.

Reorganization and Expansion of the
Human Brain

• Began at least 2-3 million years after the development of bipedal locomotion.
• Began in conjunction with scavenging and the making of stone tools.
• Marks the appearance of the genus Homo, an evolutionary offshoot of Australopithecus