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Hobbit debate goes out on some limbs

Arm and leg fossils may, or may not, come from nonhuman hominid

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3:21pm, April 19, 2010
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ALBUQUERQUE — Two fossil hobbits have given what’s left of their arms and legs to science. That wasn’t enough, though, to quell debate over hobbits’ evolutionary status at the annual meeting of the American Association of Physical Anthropologists on April 17.

Since 2004, the discoverers of unusual “hobbit” fossils on the Indonesian island of Flores have attributed their find to a pint-sized species, Homo floresiensis, that lived there from 95,000 to 17,000 years ago. These researchers also suspect, on the basis of hobbit anatomy and recent stone tool discoveries on Flores, that H. floresiensis evolved from a currently unknown hominid species that migrated from Africa to Indonesia more than 1 million years ago.

Critics say the finds represent nothing more than human pygmies like those still living on Flores. In their opinion, the centerpiece hobbit find — a partial skeleton of an adult female known as LB1 — is what’s left of a woman who suffered from a developmental disorder that resulted in an unusually small brain and a misshapen skull and lower body.

But arm and leg fossils from LB1 and a second hobbit appear robust, not unhealthy, according to a new study directed by William Jungers of Stony Brook University in New York. The bones display humanlike thickness in the tough tissue that forms the outer shell of most bones, and opposite sides of the limb bones exhibit comparable thickness, a sign of healthy growth, said Stony Brook anthropologist and study coauthor Frederick Grine, who presented Jungers’ paper at the meeting.

Hobbits also possessed much stronger limbs relative to body weight than either Homo sapiens or its presumed predecessor, Homo erectus, Jungers’ team concluded.

Limb strength for H. floresiensis approaches that previously estimated for more ancient hominid species such as the 3.2-million-year-old Australopithecus afarensis — a.k.a. Lucy — and 2.3-million-year-old Homo habilis, according to Junger’s analysis.

These results imply that hobbits were able to engage in vigorous physical activities that neither modern humans nor H. erectus could manage. Hobbits may have spent much of their time climbing trees, as Lucy’s kind did, the Stony Brook researchers propose.

Hobbits’ mix of humanlike and Lucy-like limb traits fits with Jungers’ recent proposal that a primitive, currently unknown hominid species trekked from Africa to Flores at least 1.8 million years ago and evolved into H. floresiensis. Earlier suggestions that hobbits descended from H. erectus (SN: 10/30/04, p. 275) have been dropped.

Junger’s group used computerized tomography images to calculate bone thickness at points along the length of six hobbit bones from the upper arm and the upper and lower leg. Five fossils came from LB1 and one came from another hobbit adult. The researchers then compared these data to corresponding measures for Lucy, H. habilis and several hundred people from different parts of the world, including Indonesian pygmies now living on the Andaman Islands.

Estimates of arm and leg strength for LB1 were generated by comparing her bone thickness to her height and weight — roughly 3 feet, 5 inches and 66 pounds, according to Jungers. But hobbit skeptics put LB1’s height at 4 feet or more, a stature that would imply weaker limbs than the Stony Brook researchers contend.

In another meeting presentation, Robert Eckhardt of Pennsylvania State University in University Park argued that a developmental disorder produced a suite of skeletal abnormalities in LB1 (SN: 11/18/06, p. 330), including irregularly shaped hip joints and tube-shaped upper leg bones. Junger’s new limb-bone analysis doesn’t address those points, Eckhardt said.

A variety of developmental disorders produce skeletal traits in people today that Jungers has labeled as exclusive to H. floresiensis, Eckhardt added.

At the meeting, he described the case of a woman with a developmental disorder that resulted in an S-shaped collar bone. Jungers’ team includes this characteristic in a list of hobbit-specific skeletal features.

This new twist in the hobbit controversy follows the March 17 online publication of a paper in Nature concluding that hominids reached Flores by 1 million years ago. Excavations on Flores yielded stone tools from sediment dating to that time, reported Adam Brumm of the University of Wollongong in Australia.

Brumm previously uncovered 800,000-year-old stone artifacts on Flores (SN: 6/3/06, p. 341). He now suspects hominids reached the island as early as 2 million years ago.

Brumm’s contention has been challenged by colleagues who believe natural processes may have moved the artifacts from younger to older sediment layers.

Earthquakes and flooding are two of many possible ways in which stone artifacts could have been moved on Flores, noted James Phillips of the University of Illinois at Chicago.

If Brumm is right, only further fossil finds can determine what type of hominids reached Flores by 1 million years ago, remarked Robin Dennell of the University of Sheffield in England. “Until we get that evidence, we’re stumbling in the dark,” he says.

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