A paleontological discovery – called the “breakthrough” find of 2009 by the academic journal Science – led by U. California-Berkeley professor of integrative biology Timothy White is now being contested by two teams of researchers.

Last October, White and a team of scientists announced that they had reconstructed the skeleton of the oldest known hominid – a 4.4 million-year-old female skeleton of Ardipithecus ramidus, nicknamed Ardi – but two articles published Friday in the journal Science challenge their conclusions.

Primatologist Esteban Sarmiento of the Human Evolution Foundation in New Jersey contested Ardi’s place in the human lineage, saying the fossil lived before humans began evolving separately from apes, while another group of scientists challenged conclusions drawn about Ardi’s habitat.

“Unique skeletal characters diagnostic of the hominid lineage have been well documented,” Sarmiento said in an e-mail. “White et al has failed to show Ardipithecus has any hominid diagnostic shared derived characters. Genetics and anatomy suggests A. ramidus predates the human-African ape divergence.”

According to White, who was credited with the 1974 discovery of the 3.2 million-year-old hominid Lucy, Ardi was classified as a hominid based on dental, cranial and postcranial evidence. Sarmiento’s estimate puts the divergence of humans from African apes at approximately three to five million years ago, but a response written by White and his team argues that this estimate is not accurate.

White and his team also said that Ardi dwelled in a woodland environment, which could possibly disprove the evolutionary theory that human ancestors started walking on two feet in order to adapt to a savanna environment.

But according to a group of anthropologists and geologists led by Thure Cerling, a professor of geology and geophysics at the University of Utah, Ardi’s habitat is more accurately represented by “tree or bush-savanna, with 25 percent or less woody canopy cover.”

In response to the criticism, White and his team published an article saying a savanna environment was inconsistent with evidence collected from fossil, geological and geochemical sources.

“One of the main problems with the way they approached the criticism is that they were taking our statements as absolutes and taking them out of context,” said Stanley Ambrose, a co-author of the response and professor of anthropology at the University of Illinois.

With a discovery of this magnitude, contention was expected, said White.

“There are two key parts of science, the creative and the critical, so any interpretations as major as those we published last October are bound to generate some criticism,” he said in an e-mail. “Such debate can sometimes even produce new ideas to be tested with new data.”