The Elements of Evolution (58-2) Australopithecus continued

Au. anamensis

Au. anamensis first made the scene 4.2 MYA, lasting to 3.9 MYA. Its thick enamel teeth suggest a diet of nuts, seeds, fruits, and leaves. Au. anamensis was a tree climber. How bipedal it was remains unsettled.

Au. afarensis

Au. afarensis (3.9–2.9 MYA) likely descended from Au. anamensis. Au. afarensis fossils have been found only in east Africa.

Cranial capacity to body mass was 1.2%, compared to 2.75% in humans today – roughly 1/3rd the brain size. Essentially, the anatomy of Au. afarensis appears apelike above the neck and humanlike below. Au. afarensis illustrates mosaic evolution: a variety of adaptive changes in separate places at disparate rates during different times.

There is no doubt that Au. afarensis walked upright: ranging the savannas and open woodlands, eating foraged fruits, seeds, sedges, and roots. Still, Au. afarensis retained a fondness for trees, where it spent much of its time.

Lucy is a famous Au. afarensis fossil find: a nearly complete female skeleton, 25 years old when she died 3.18 MYA.

Another find – a female juvenile dubbed Selam by its discoverers – suggests that Au. afarensis mixed walking with climbing. Selam’s shoulder blades and socket indicate adaptation for frequent tree-climbing. Selam presents an interpretive challenge. A terrestrial lifestyle while retaining some shoulder characteristics of earlier tree-climbing hominins is possible. Despite their similarities, Lucy and Selam may not have been the same species.

Au. afarensis had stone tools and practiced butchery. Ungulate bones found near Selam appear to have been cut by stone tools. But Au. afarensis lacked the manual dexterity to craft stone tools. Its hand proportions were more like gorillas than later hominins. While Au. afarensis may have been able to bring the tips of its fingers and thumb together, its thumbs were too short for the precision grip that later hominins had, enabling them as tool makers.

Like Ardipithecus ramidus, Au. afarensis were only moderately sexually dimorphic. Adult males stood ~1.6 meters and weighted 45 kg. Females were a bit smaller and less heavy. Males also typically displayed large crests at the top of their skulls; females did not.


Closely related hominin species shared the planet many times in the past few million years. ~ American paleontologist Bernard Wood

Au. afarensis had contemporaneous cousins. Besides closely related species in east Africa, one known relative was in North Africa; the other in the far south.

 Lucy’s Northern Cousin

A 3.5-million-year-old foot fossil found in Ethiopia reveals a species like Ar. ramidus, at least from the ankle down. While Lucy walked about much of the time, this northern species had feet for climbing trees and grasping limbs. It would have walked awkwardly.

 Lucy’s Southern Cousin

A nearly complete fossil skeleton dating to 3.67 MYA was found in South Africa’s Sterkfontein Caves in the mid-1990s. Similar partial skeletons had already been discovered at a nearby site in 1948. This small-footed hominoid with a flat face is known as Australopithecus prometheus.

 Lucy’s Next-Door Neighbor

Current fossil evidence clearly shows that there were at least 2, if not 3, early human species living at the same time and in close geographic proximity. ~ Ethiopian paleoanthropologist Yohannes Haile-Selassie

3.4 MYA jaw fossils were found in Ethiopia in 2011, showing that Lucy had a nearby relative with a quite different diet. The species was dubbed Australopithecus deyiremeda.

Au. bahrelghazali

Au. bahrelghazali is a controversial 1993 discovery by French paleontologist Michel Brunet. His find was a single specimen, dated 3.6 MYA. It has been the only australopithecine fossil found in central Africa. All others are from east Africa, some 2,500 km distant.

Au. bahrelghazali has similar dentistry to Au. afarensis, but is more like Sahelanthropus in the shape of its skull.

Stingy Brunet classified his find as a separate species, but refuses to let others examine the remains, contrary to the International Code of Zoological Nomenclature.

Au. africanus

Au. africanus, which lived in southern Africa, dates to 3.3 MYA. Au. africanus was a significant step from Au. afarensis. Several anatomical features were significantly more like the Homo genus, including a larger cranium (400–625 cm2), gracile (slender) build, and more humanlike hands.

Au. africanus had a pelvis that was better built for walking than Au. afarensis. Yet Au. africanus retained the apelike curved fingers of tree climbers.

The diet of Au. africanus seems to have been seasonal, favoring fruit, though able to chew seeds and other food requiring mastication.

Sexual dimorphism showed in spinal adaptation of females to bear lumbar loads upright while pregnant.

Like chimpanzees, Au. africanus had patrilocal communities: in reaching sexual maturity, females emigrated to find mates.

Au. garhi

A. garhi was a gracile species that lived 2.5 MYA. Large molars and pre-molars suggest a diet of tough, fibrous foods: perhaps tubers and other chewy vegetables. Au. garhi shaped stone tools. Only a single find of cranial fragments has been made of Au. garhi, in Ethiopia. Much mystery remains.

Au. sediba

Au. sediba represents an amalgam. Fossils date to 2 MYA. Evident adaptations include better walking, even running, and a surprisingly modern hand capable of a precision grip. Vestiges of the past remained, albeit with a twist. Au. sediba had long arms, climbed trees, and walked upright but had a different gait from that of either chimps or humans. This suggests that several forms of bipedalism evolved among hominids.

While Au. sediba had a humanlike lower rib cage, its lower back was longer and more flexible than people today. Au. sediba brain size was on par with other australopiths (420–450 cm2), but the cranial shape presaged modern humans.

Au. sediba lived in woodlands, eating fruit, tree leaves, and bark. Au. sediba teeth were like Au. africanus; perhaps an instance of parallel evolution, as Au. sediba had no links to earlier hominins often regarded as Homo ancestors, notably Au. afarensis. Au. sediba may have simply been one of several different australopiths living at the time.