• 8 mya: fossil apes• 3.5 mya: Australopithecus afarensis• Cimpanzee-human divergence estimated from

genetic data at around 5 mya.• Gap in fossil record when this hypothetical

divergence occurred.• Looking for hominids with bipedality and a non-

honing chewing complex.• Then, fossils from the critical time-gap were

discovered—the pre-australopithecines.

Hominid traits: non-honing chewing; bipedalism

Rocky Mountain News - July 11, 2002

Rocky Mountain News - July 11, 2002

Sahelanthropus tchadensisBrain: 350 ccMassive brow ridgeForamen magnum forwardNonhoning complex

6-7 mya

The habitat: woodland

Orrorin tugenensisc. 6 myaBones of 5 individualsA finger bone, curved: ancestral characteristic (arboreal)The habitat: woodland

FemurEvidence ofbipedalism

And then!Ardipithecus kadabba (Early): 5.8—5.5 myaArdipithecus ramidus (Late): 4.4 myaProbably anagenesis

• Significance: time of existence• On the human lineage just after the chimpanzee-human split.

• Early: CP3 honing complex like chimpanzee

• Late: honing complex gone

Chimpanzee and Ar. kadabba

Science October 2009Dedicated to 11 papers onA. ramidus

• Bones from a sedimentary rock stratum

• c. 3 m thick (100-10,000 time range)

• Sandwiched between two layers of tuff

• Laser fusion 39Ar 40Ar dates of 4.4 my

Estimates4 ft. tall110 lbs.

♀ Last commonancestor ofchimpanzees andhumans was notchimpanzee-like

palmigradeclambering +rudimentarybipedalism

Opposable big toe (ape like)But foot lacks flexibility

Foot

Three groups that disappeared

Australopithecus aethiopicus

Temporal fossa

Sagittal crest

Zygomatic arch

boisei

robustus

boisei

aethiopicus

Australopithecus africanus

Australopithecus robustus +Au. boisei

Teeth: surface patterns

Importanthominins

aethiopicus

afarensis

boisei

africanus

robustusHomo habilis

Australopithecines

• Australopithecus anamensis (4.2 mya)– basal to other australopithecines)– definitive evidence of bipedalism

• Considered to be in the human lineage.

Australopithecus afarensis“Lucy” (Hadar, Ethiopia)

3 year oldchild

Australopithecus afarensis3.6-3.0 mya

Adult

3.6 mya

Australopithecusafarensis?

Why?

Large toe in line with the other toes

Hominid foot characteristic

Australopithecus garhi2.5 mya