Bones of "Ardi," New Human Evolution Fossil, "Crushed Nearly to Smithereens" - Evolution News & Views

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Bones of "Ardi," New Human Evolution Fossil, "Crushed Nearly to Smithereens"

Another new alleged missing link has been found, if you consider something discovered in the early 1990's new. This fossil seems to have spent almost as much time under the microscope at Berkeley as it did in the ground in Ethiopia, when it was first buried about 4.4 million years ago.

Why did it take over 15 years for the reports on this fossil to finally be published, besides the fact that it allowed more time for planning the now-customary PR campaign? A 2002 article in Science explains exactly why: the bones were so brittle, "squished," "chalky" and "erod[ed]" when cleaned such that many of the bone fragments had to be "reconstruct[ed]"--and that took a long time. Here's the story from more than seven years ago:

[I]n 1992, the Middle Awash Research Team, co-led by [Tim] White, made a discovery that ended Lucy's reign. About 75 kilometers south of Lucy's resting place, at Aramis in the Afar depression of Ethiopia, the team found fossils of a chimp-sized ape dated to about 4.4 million years ago. ... The team named this species Ardipithecus ramidus, drawing on two words from the Afar language suggesting that it was humanity's root species. But skeptics argue that the published fossils are so chimplike that they may represent the long-lost ancestor of the chimp, not human, lineage.

The next field season, team member Yohannes Haile-Selassie found the first of more than 100 fragments that make up about half of a single skeleton of this species, including a pelvis, leg, ankle and foot bones, wrist and hand bones, a lower jaw with teeth--and a skull. But in the past 8 years no details have been published on this skeleton. Why the delay? In part because the bones are so soft and crushed that preparing them requires a Herculean effort, says White. The skull is "squished," he says, "and the bone is so chalky that when I clean an edge it erodes, so I have to mold every one of the broken pieces to reconstruct it." The team hopes to publish in a year or so, and White claims that the skeleton is worth the wait, calling it a "phenomenal individual" that will be the "Rosetta stone for understanding bipedalism."

(Ann Gibbons, "In Search of the First Hominids," Science, 295:1214-1219 (February 15, 2002).)

Of course a key feature in demonstrating that an organism was bipedal is the precise shape of its pelvis. But look at what one of the current media stories on A. ramidus is reporting about the original condition of the pelvis that was discovered:
One problem is that some portions of Ardi's skeleton were found crushed nearly to smithereens and needed extensive digital reconstruction. "Tim [White] showed me pictures of the pelvis in the ground, and it looked like an Irish stew," says Walker. Indeed, looking at the evidence, different paleoanthropologists may have different interpretations of how Ardi moved or what she reveals about the last common ancestor of humans and chimps.

(Michael D. Lemonick and Andrea Dorfman, "Excavating Ardi: A New Piece for the Puzzle of Human Evolution," Time Magazine (October 1, 2009).)

The recent news report in Science recounts the same problems with the fossil:
But the team's excitement was tempered by the skeleton's terrible condition. The bones literally crumbled when touched. White called it road kill. And parts of the skeleton had been trampled and scattered into more than 100 fragments; the skull was crushed to 4 centimeters in height.

(Ann Gibbons, "A New Kind of Ancestor: Ardipithecus Unveiled," Science, Vol. 326:36-40 (Oct. 2, 2009).)

National Geographic put it thus:
After Ardi died, her remains apparently were trampled down into mud by hippos and other passing herbivores. Millions of years later, erosion brought the badly crushed and distorted bones back to the surface. They were so fragile they would turn to dust at a touch.
"Chalky"? "Squished"? "Badly crushed and distorted"? "Needed extensive digital reconstruction"? After all the media hype and overblown claims about importance of Ida, forgive me for having an initial reaction of skepticism. How far would you trust a "Rosetta stone" that was initially "crushed to smithereens" and "would turn to dust at a touch"?

Claims of bipedalism often depend upon precise measurements of the angles of key bones such as the pelvis, femur, and knee-bones. But if these bones were discovered in such a crushed, squished, etc. form, determining the precise contours of these bones might become a highly subjective exercise. I'm sure they spent a lot of time on their reconstructions (and it certainly sounds like they did) but at the end of the day, it's difficult to make solid claims about extremely unsolid bones.

Anyone for some Irish stew?


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