Some of the world’s most prominent anthropologists are butting heads over whether the recent discovery of a 7 million-year-old skull is in fact the oldest remnant of a pre-human ancestor.

The so-called Toumai skull, whose discovery was announced in July, was unearthed last year in central Africa in what some described as the most startling fossil find in decades. The remarkably intact specimen has a thick brow and flat face, and is believed to be between 6 and 7 million years old.

The research team that found it, led by French paleontologist Michel Brunet, calls the skull a remnant of the earliest known hominid, or pre-human ancestor.

But in a strongly worded article in today’s journal Nature, anthropologists Brigette Senut, Milford H. Wolpoff, Martin Pickford and others say that the skull is not on the human branch of the evolutionary tree. Instead, they say, the specimen may be that of an early female gorilla or a chimpanzee, or a species that has since become extinct.

“I don’t see how you can tell what it is. But it is not human,” said Wolpoff, a University of Michigan anthropologist.

The critics took special note of scars left by neck muscles that might give indication that it was a biped, a critical defining feature of the human family.

“In looking at the scars, they told us quite clearly that this animal did not habitually walk erect. It did not have human posture, therefore it is not human,” Wolpoff said.

The Toumai skull was found in July in Chad. A group of scientists disputes the assertion that the skull is of a hominid.

Despite claims to the contrary by Brunet and his team, the size and shape of the teeth and brow are not necessarily characteristic of a hominid, Senut and the others write.

It’s the latest missive in a feud that developed shortly after the Toumai discovery, and shows no signs of abating.

Senut, of the Natural History Museum in Paris, has her own stake in the debate. Last year, she led a French team of researchers that described remains of a new species, Orrorin tugeneniss, which they claimed represented a hominid species. At the time, it was believed to be the oldest trace of a human ancestor. But Brunet’s discovery and another one last year would be older if they truly are hominid ancestors.

In a response in Nature, Brunet writes that his critics are wrong in their description of Toumai’s facial characteristics and teeth. He also says they provide no evidence that the skull is that of an ape, “nor have they disproved any derived feature that this species shares with later hominids.” And parts of their argument, he says, are simply “flippant.”

Brunet has sparred with the same critics before. At a news conference shortly after announcing the find last summer, Brunet told reporters: “If one or two people somewhere disagree with me, that is their problem. But one cannot confuse this with a gorilla.’