Human ancestor gets digital facelift

For example, Bromage said, take any mammal and draw an imaginary line from the last permanent molar in its jaw that extends towards the opening of the ear and out the center of the eye socket. The angle of that line should be around 45 degrees.

“What this does is distribute the senses in a very specific way,” Bromage explained.

In the original KNM-ER 1470 reconstruction, this angle was between 60 and 75 degrees, Bromage said. “It was absolutely incompatible with life,” he said. “The jaw would have been positioned so far back in the skull that there would have been no room for an airway or esophagus. It couldn’t breathe or eat.”

Bromage presented his team’s findings at the annual meeting of the International Association for Dental Research last week and is submitting the results to a scientific journal for peer review later this year.

Smaller brain too?
The new reconstruction suggests H. rudolfensis’ jaw jutted out much farther than previously thought. The researchers say the cranial capacity of a hominid can be estimated based on the angle of the jaw’s slope and they have downsized KNM-ER 1470’s cranial capacity from 752 cubic centimeters to about 526 cc. (Humans have an average cranial capacity of about 1,300 cc.)

But not everyone agrees that brain size can be inferred from jaw protrusion. Biological anthropologist Robert Martin, of the Field Museum in Chicago, said the researchers “may well be right” in their reconstruction of the face, but said the researchers’ claims about being able to estimate cranial capacity from facial features are “crazy.”

“What they’re claiming is you stick the face out, and because the face sticks out more the brain capacity has to be less. I don’t follow that at all,” said Martin, who is an expert on hominid skulls and who was not involved in the study.

“They haven’t changed the skull at all; they’ve simply rotated the face outwards,” Martin added.

Martin also disputes the claim that H. rudolfensis’ large cranial capacity made it stand out among ancient hominids. Martin points out that a 1.6 million-year-old Homo erectus skeleton known as “Turkana Boy” had a cranial capacity of about 900 cc.

“At 1.9, you’ve got [H. rudolfensis] with [a cranial capacity] of 750 cc, and at 1.6 you’ve got 900 cc. I don’t have a problem with that,” Martin said.

If confirmed, KNM-ER1470’s new cranial capacity would be comparable to that of H. habilis. “Now it’s no longer an outlier,” Bromage said. “It’s just part of the gang.”

It would also suggest humans developed their characteristically large brains and flatter faces at least 300,000 years later than previously thought, perhaps as recently as 1.6 to one million years ago when H. erectus and another later hominid, Homo ergaster, lived.

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