WASHINGTON (Reuters) - Tiny skeletons found in the caves of the Pacific islands of Palau undercut the theory that similar remains found in Indonesia might be a unique new species of humans, researchers reported on Monday.
The Palau skeletons, which date to between 900 and 2,800 years ago, appear to have belonged to so-called insular dwarfs -- humans who grew smaller as a result of living on an island, the researchers said.
They said their findings, published in the Public Library of Science journal PLoS ONE, show it is possible the same thing happened on the Indonesian island of Flores, where small skeletons dating back 15,000 to 18,000 years ago have intrigued scientists since they were discovered in 2004.
Some groups have proposed that the Flores humans, who would have been about three feet (one meter) tall as adults, represented a distinct species called Homo floresiensis.
Others argue they were small because of nutritional deficiencies, genetic defects or because they were similar to pygmies, dwarfs or other shorter types of people.
Lee Berger of the University of the Witwatersrand in Johannesburg, South Africa, and colleagues say they cannot explain the Flores skeletons, but said they found some similar remains in Palau, one of the islands of Micronesia.
"These rock islands contain numerous caves and rock shelters, and many of these sites contain abundant fossilized or subfossilized human remains," they wrote in their report, published on the Internet here"At least ten burial caves have been discovered in the rock islands, and excavations at one of them (Chelechol ra Orrak) has produced the skeletal remains of at least 25 individuals," they added.
Like the skeletons found on Flores, these are very small, with small heads and some features that are considered primitive for modern Homo sapiens, Berger's team said.
They are smaller even than living pygmies, they added.
One adult male would have weighed around 95 pounds (43 kg) and one female would have weighed around 64 pounds (29 kg), they estimated.
Such "insular dwarfism" has been seen in several species of animals including extinct mammoths and elephants from islands off Siberia, California and the Mediterranean.
The Palau skeletons are clearly modern humans, however, the researchers note. They cannot closely examine the skulls yet as they are embedded in rock. The Flores skeleton had very small skulls with tiny brain cases.
(Reporting by Maggie Fox, editing by Will Dunham and Philip Barbara)