Anthropology 1: Lecture 9

Late Miocene Potential Protohominins

Sahelanthropus tchadensis

TM 266-01-060

“Toumaï”Found in 2001 by

Ahounta Djimdoumalbae

6-7 my old

Cranial capacity

320-38 cc.

• Described by Michel Brunet of University of Poitiers.

• Supraorbital torus and small canines are hominin-like.

• Brunet argues on the basis of the position of the attachment areas for neck muscles that it was an upright biped.

However, critics argue that the foramen magnum is positioned towards the back of the skull, as in the modern apes

Orrorin tugenensis “Original Man”

Found in 2000 in the Tugen hills in central Kenya by Martin Pickford and Brigitte Senut of the Museum of Natural History in Paris

Date: 5-6 million years old (potassium argon/ Ar39-Ar40)

Remains of 5 individuals were found.

The hominin was the size of a female chimpanzee.

To Senut the femur reflects bipedalism while the humerus indicates tree-climbing.

Molars have thick enamel, but are relatively small compared to Australopithecus.

Ardipithecus ramidus

Found in 1992-93 by Timothy White, Gen Suwa, and Berhane Asfaw of UC Berkeley at Aramis in the Middle Awash region of the Afar triangle, Ethiopia.

Name means “ground man-root” in the Afar language.

Dates range between 3.85 – 5.55 mya (Late Miocene to Early Pliocene).

Initially 17 specimens, including teeth, portion of a child’s mandible, bones of the left arm, and portion of the basi-cranium were discovered.

A partial skeleton (45% complete) of a female was also found in ’94 (Ara-Vp-6/500).

Individuals were c. 4’ tall, and were only slightly dimorphic to judge from canine size.

Published by AAAS

T. D. White et al., Science 326, 64, 75-86

Fig. 3 The ARA-VP-6/500 skeleton

Preserved bones include portions of the cranium and teeth, pelvis, ulna and radius, hindlimbs, wrists, ankles, hands and feet.

Cranium is said to be similar to Sahelanthropus; cranial capacity 300-350 cc.

A case is made for bipedalism on the shape (short) and orientation of the ilia (sagittal) of the pelvis and expanded 2nd metatarsal base in foot. It had a fully abductable hallux.

In the trees its mode of locomotion would have been palmigrade clambering, as evidenced by the dorsiflexion capabilities of the wrist. This mode of locomotion is seen in Miocene, but not modern, apes.

Ilium

hallux

2nd metatarsal

Sagittal region

• Some scientists doubt that Ardi’s feet were capable of bipedal locomotion

Published by AAAS

T. D. White et al., Science 326, 64, 75-86

Fig. 4 Comparisons of Ardipithecus (left) and early Australopithecus (right)

Ardipithecus lacked the megadonty of Australopithecus.

It had narrow molars capped with enamel intermediate in thickness between an ape’s and a hominin. It was apparently an omnivore.

Implications of Ardipithecus

• Pairbonding may have been significant.• Ardipithecus occupied a forested niche, so

bipedalism emerged in the forests.• Common ancestor with African apes lived 7-10

million years ago given primitive features of Ardipithecus forelimbs and wrists.

• White believes it is impossible to determine whether or not any fossil species is a direct ancestor of any other species.