Professor Mike Morwood, of the University of New England, in Armidale, Australia, stunned the science world last year when he and his team announced the discovery of 18,000-year-old remains of a new human species called Homo floresiensis.
The partial skeleton discovered in a limestone cave on the remote Indonesian island of Flores in 2003 was of a tiny adult hominid, or early human, only one meter (3 feet tall), that would have walked upright and had a chimpanzee-sized brain.
Morwood and his team said it represented a unique species of early humans that evolved to a naturally small size because of environmental conditions and the isolation of the island, which was also home to exotic creatures such as miniature elephants and Komodo dragons.
But critics suggested the small hominid was not a new species and was more likely a pygmy human or a creature that suffered from a form of microcephaly, a condition that causes an unusually small brain.
'The finds further demonstrate ...(it) is not just an aberrant or pathological individual but is representative of a long-term population,' Morwood and his team said in a report in the science journal Nature.
The newly found remains, dug up in 2004, consist of a jaw, as well as arm and other bones which the researchers believe were from at least nine individuals.
A jaw bone reported last year and the latest one were probably from the same species, according to the scientists. Both share similar dental features and lacked chins.
The new species, dubbed "Flores man," is thought to be a descendent of Homo erectus, which had a large brain, was full-sized and spread from Africa to Asia about 2 million years ago.
"Although the original skeleton is estimated to be 18,000 years old, a child's radius (arm bone) was found in deposits estimated to be 12,000 years old," Daniel Lieberman, of Harvard University in Massachusetts, said in a commentary in the journal.
He added that if the remains were from a population of short microcephalic humans they would have had to survive a long time or been susceptible to a high frequency of dwarfism.
"Such possibilities strain credulity," Lieberman added.
CAT scans of the inside of the skull found in 2003 suggested it was a normal adult and not a diseased or mutant species. The brain could have been advanced enough for tool-making.
But Robert Martin, provost and vice president of academic affairs at the Field Museum in Chicago, Illinois is unconvinced.
"Whatever else is true, that brain is simply too small for an 18,000 year-old hominid," he told Reuters.