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Are they all the same species?

The fossil sites of Hadar, Ethiopia, and Laetoli, Tanzania

Could the fossils found at Laetoli and Hadar, roughly a thousand miles apart and spanning more than half-a-million years, have belonged to the same species? Each of the four dig sites reveals only a partial picture: Lucy, while a 40 percent complete skeleton, has only fragments of a skull. The skull found at Hadar in 1992 has no body. The Laetoli prints are like the shadows of invisible creatures.

The difference in size between Lucy's petite bones and more massive ones found at Hadar also puzzled paleoanthropologists. But careful analysis of thousands of fossils, and a remarkable discovery, helped resolve the debate.

In the summer of 1977, collaborators Donald Johanson and Tim White got together with a roomful of ancient hominids from Hadar and Laetoli. In addition to the famous footprints, they had two well-preserved jaws and isolated teeth from Laetoli. From Hadar, they had not just Lucy but a host of hundreds of fossils, including a knee joint that strongly suggested its owner walked upright.

But the find that may have been most critical for relating the various fossils to one another was the First Family. Here were the remains of 13 individuals -- likely 9 adults and 4 children, judging from their teeth and jaws. If they all were entombed together, perhaps by a flash flood, they likely all belonged to the same social group. And if they were an "extended family," they were certainly all the same species. The adults of this group varied tremendously in height and heft, leading White and Johanson to conclude that the males of this species were tall and bulky compared to the females, like gorillas are today.

Johanson and White announced at a 1978 symposium in Stockholm that Lucy, the people of Laetoli, the First Family, and other finds all belonged to a single species: Australopithecus afarensis, the Southern Ape from Afar. Anthropologists today continue to debate whether all of the individuals of the First Family were truly buried together, and whether all of the Hadar and Laetoli finds are truly members of the same species. Yet many agree that A. afarensis was a critical species in the story of human evolution, and likely the common ancestor to all later branches of humanity, including our own.

Details of the fossil evidence

Lucy: jaw
Lucy had a much smaller and more V-shaped jaw than the owner of the Hadar skull. She also may have been nearly a foot shorter than some members of the First Family. Yet this size difference can be explained by sexual dimorphism: Males of this species may have been robust in stature compared to their female counterparts.

Hadar Skull: various features
Many features of this well-preserved skull can be seen in the fragments collected for the First Family and Lucy. The individuals who died at all three sites had similarly shaped jaws, teeth, and braincases.

Laetoli Footprints: prints
The upright walking creatures who made these prints likely had knee and hip joints like those of Lucy and the members of the First Family. Using a model foot based on fossils from Hadar, researchers were able to make prints much like this one.

First Family: various teeth and bones
The wide range in body size among this one group of individuals lead many anthropologists to think that Lucy, the Hadar skull, and other finds could be from the same species. Some scientists suspect that one "extended family" of 13 individuals was entombed together in a flash flood; the fossils of the First Family show few signs of weathering or attack by predators.

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Intro | How did they move? | What did they look like? | Are they all the same species? | When did they live?