2-million-year-old fossils raise hope over 'missing link'

ByABC News
September 8, 2011, 6:53 PM

— -- A new analysis of bones that are nearly 2 million years old suggests they come from a species that may be a leading candidate as an ancient ancestor to humans, paleontologists reported Thursday.

Calling the ape-like species Australopithecus sediba, South African team leader Lee Berger of the University of the Witwatersrand in Johannesburg suggests that many "human" traits — long thumbs, upright walking, wide hips — evolved from this vanished species. This may represent "the best candidate for the ancestor" to people as any other species considered a front-runner to date, Berger says.

Africa is the birthplace of humanity, where Australopithecine ("southern ape") precursors to humans and modern apes originated over several million years, as shown by fossils and genetic evidence. The South African fossils are among the best-preserved examples.

"They are important fossils and remarkably detailed," said paleontologist Bernard Wood of George Washington University in D.C., who was not part of the discovery team. Wood, along with other paleontologists, expressed caution at the report team's human kinship claim. "I have some resemblances to Warren Buffett, but I'm not a billionaire," Wood says. "A few resemblances does not an ancestor make."

About 4 feet tall , fossils of Australopithecus sediba ( "southern wellspring ape") were discovered in 2008 and first reported last year from the Malapa site in South Africa, a series of exposed ancient caves. The vanished species climbed trees like orangutans and walked on the ground like people. In five papers published in the journal Science, the discovery team takes an in-depth look at the fossil's human-like features:

• Fossil hands reveal long thumbs and wrists resembling human ones, which would enable tool use. Curved fingers look more ape-like.

• Foot bones reveal an upright-walking stance like people, while ankle bones belong to a tree-climber.

• Pelvis reconstructions reveal broad hips, "argued by some as a development that allowed human ancestors to birth large-brained babies," says team scientist Job Kibii, also of the the University of the Witwatersrand.

• The brains were less than one-third the size of a modern human's, but features preserved on their inner skull, the team suggests, resemble precursors to specialized brain areas found in modern humans .

However, fossil brain expert Dean Falk of the School for Advanced Research in Santa Fe, N.M., and Florida State University in Tallahassee, questions how different the fossils' brains are compared with other Australopithecines. "What is needed is a thorough, well-illustrated comparative study," she says, by e-mail.

Wood suggests that the newly described fossils may simply illustrate one of the varied forms that pre-human species took long ago in Africa. With their human-like traits, the fossils were nearly contemporary with the large-brained tool-using early human species, Homo erectus ("upright man") dating to about 1.8 million years ago. "I don't know if we will ever be certain about a common ancestor," Wood says. "We may always be looking."