Early Hominins

3

Evolution of Bipedalism

in Hominins

Quadrupedalism to two leg walking

Features Associated with Bipedalism

S shaped spine, broad short pelvis, Bicondylar Angle of the Femur (plastic trait), Longitudinal Arch and Adducted Hallux (big toe)

Where and how old was the Sahelanthropus tchadensis

Location: Toros Menalla, Chad

Age: Between 6 and 7 Ma

what were some characteristics of the skull of Sahelanthropus tchadensis

Large supraorbital torus, Sagittal crest, Brain Volume

~350cc, Orthognathic

(flat) face, Anteriorly

placed foramen

magnum, Strong

postorbital

constriction, Small canines

Where and how old are Orrorin tugenensis

Location: Lake Baringo, Kenya

Age: 6Ma

What are some traits of Orrorin tugenensis

• Mix of traits for arboreal

behavior and bipedalism

• Femur, in particular the

femoral neck, show shape

changes associated with

walking upright

• The humerus and phalanges

show features associated with

climbing

what were the two species of Ardipithecus and where and how old were they?

Location: Aramis, Ethiopia

Two species:

• Ar. kadabba

Age: 5.6Ma

• Ar. ramidus

Age: 4.4Ma

- Best known of the two

species

- One relatively complete

skeleton

- Remains of at least 30 other

individuals

Characteristics of the skull of a Ardipithecus ramidus

Anteriorly positioned foramen magnum, Brain volume ~350cc, Thin supraorbital

torus, Reduced canine size

Ardipithecus ramidus pelvic characteristics

• The upper pelvis looks more similar to

modern humans indicating side-to-side

balance mechanism

• The lower pelvis looks more

ape-like with features for

climbing