Tuesday, February 15, 2011

Another reason to love Lucy.

A metatarsal bone indicates that A. afarensis had stiff, arched feet.

I already wrote about this scientific discovery here.

Today's Tuesday 2/15/2011 Science Times of the New York Times has an article about the same fossil.

Lucy may well be the world’s most famous fossil hominid. She is the best-known specimen of the species Australopithecus afarensis, and her partial skeleton, found in 1974, revealed that she and her kin could walk upright.

But because of a lack of foot bone specimens, scientists have long debated how well she walked — that is, whether A. afarensis also used a grasping movement with the feet, as apes do when they grab tree branches.

Now, a fossilized foot bone from Hadar, Ethiopia, reveals that A. afarensis had arched feet, as do modern humans, and was fully committed to walking upright. The species lived between 3.7 million and 2.9 million years ago.

Researchers from the University of Missouri and Arizona State University report these findings in the journal Science.

The newly found specimen is a well-preserved fourth metatarsal, one of the long bones that connect the toe to the base of the foot.

The bone is more similar to the modern human foot than to that of apes, and it suggests that the A. afarensis foot had a well-formed arch that was shock-absorbing.

“One little tiny bone of the foot tells us a good, long story,” said Carol V. Ward, the study’s lead author and a biologist at the University of Missouri. “They couldn’t grab on to much, and they were walking just like we were.”

Until two years ago, Lucy was the earliest known skeleton from the human branch of the primate family. She was replaced by Ardi, who belongs to the species Ardipithecus ramidus and lived 4.4 million years ago. Unlike Lucy, Ardi most likely walked both upright and on all fours.


More information about the same fossil from http://www.sciencemag.org/content/331/6018/750.abstract

Complete Fourth Metatarsal and Arches in the Foot ofAustralopithecus afarensis

The transition to full-time terrestrial bipedality is a hallmark of human evolution. A key correlate of human bipedalism is the development of longitudinal and transverse arches of the foot that provide a rigid propulsive lever and critical shock absorption during striding bipedal gait. Evidence for arches in the earliest well-known Australopithecus species, A. afarensis, has long been debated. A complete fourth metatarsal of A. afarensis was recently discovered at Hadar, Ethiopia. It exhibits torsion of the head relative to the base, a direct correlate of a transverse arch in humans. The orientation of the proximal and distal ends of the bone reflects a longitudinal arch. Further, the deep, flat base and tarsal facets imply that its midfoot had no ape-like midtarsal break. These features show that the A. afarensis foot was functionally like that of modern humans and support the hypothesis that this species was a committed terrestrial biped.


A drawing of another human ancestor, ARDI, can be found at this post.

The New York Times had an article about ARDI on October 1, 2009:

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