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Thursday, May 21, 2009

Fossil Ida: extraordinary find is 'missing link' in human evolution

Perfectly preserved fossil Ida, unveiled in New York today, provides unprecedented insight into our ancestry

Ida the missing link primate fossil - whole skeleton

Ida, one of the most complete primate fossils ever found, a 47-million-year-old human ancestor. Photograph: Atlantic Productions Ltd

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Scientists have discovered an exquisitely preserved ancient primate fossil that they believe forms a crucial "missing link" between our own evolutionary branch of life and the rest of the animal kingdom.

The 47m-year-old primate – named Ida – has been hailed as the fossil equivalent of a "Rosetta Stone" for understanding the critical early stages of primate evolution.

The top-level international research team, who have studied her in secret for the past two years, believe she is the most complete and best preserved primate fossil ever uncovered. The skeleton is 95% complete and thanks to the unique location where she died, it is possible to see individual hairs covering her body and even the make-up of her final meal – a last vegetarian snack.

"This little creature is going to show us our connection with the rest of all the mammals; with cows and sheep, and elephants and anteaters," said Sir David Attenborough who is narrating a BBC documentary on the find. "The more you look at Ida, the more you can see, as it were, the primate in embryo."

"This will be the one pictured in the textbooks for the next hundred years," said Dr Jørn Hurum, the palaeontologist from Oslo University's Natural History Museum who assembled the scientific team to study the fossil. "It tells a part of our evolution that's been hidden so far. It's been hidden because the only [other] specimens are so incomplete and so broken there's nothing almost to study." The fossil has been formally named Darwinius masillae in honour of Darwin's 200th birthday year.

It has been shipped across the Atlantic for an unveiling ceremony hosted by the mayor of New York Michael Bloomberg today. There is even talk of Ida being the first non-living thing to feature on the front cover of People magazine.

She will then be transported back to Oslo, via a brief stop at the Natural History Museum in London on Tuesday, 26 May, when Attenborough will host a press conference.

Ida was originally discovered by an amateur fossil hunter in the summer of 1983 at Messel pit, a world renowned fossil site near Darmstadt in Germany. He kept it under wraps for over 20 years before deciding to sell it via a German fossil dealer called Thomas Perner. It was Perner who approached Hurum two years ago.

"My heart started beating extremely fast," said Hurum, "I knew that the dealer had a world sensation in his hands. I could not sleep for 2 nights. I was just thinking about how to get this to an official museum so that it could be described and published for science." Hurum would not reveal what the university museum paid for the fossil, but the original asking price was $1m. He did not see the fossil before buying it – just three photographs, representing a huge gamble.

But it appears to have paid off. "You need an icon or two in a museum to drag people in," said Hurum, "this is our Mona Lisa and it will be our Mona Lisa for the next 100 years."

Hurum chose Ida's nickname because the diminutive creature is at the equivalent stage of development as his six-year-old daughter. Hurum said Ida is very excited about her namesake. "She says, 'there are two Idas now, there's me I'm living and then there's the dead one.'"

"It's caught at a really very interesting moment [in the animal's life] when it fortunately has all its baby teeth and is in the process of forming all its permanent teeth," said Dr Holly Smith, an expert in primate development at the University of Michigan in Ann Arbor, who was part of the team. "So you have more information in it than almost any fossil you could think of."

The fossil's amazing preservation means that the scientific team has managed to glean a huge amount of information from it, although this required new X-ray techniques that had not previously been applied to any other specimens.

The researchers believe it comes from the time when the primate lineage, that diversified into monkeys, apes and ultimately humans, split from a separate group that went on to become lemurs and other less well known species.

Crucially though, Ida is not on the lemur line because she lacks two key characteristics shared by lemurs – a grooming claw on her second toe and a fused set of teeth called a tooth comb. Also, a bone in her ankle called the talus is shaped like members of our branch of the primates. So the researchers believe she may be on our evolutionary line dating from just after the split with the lemurs.

According to the team's published description of the skeleton in the journal PLoS ONE, Ida was 53cm long and a juvenile around six to nine months old. The team can be sure Ida is a girl because she does not have a penis bone.

"She was at this vulnerable age where you are no longer right with your mother," said Smith, "Just as you leave weaning you are not full grown, but you are on your own."

The unprecedented preservation of Ida meant working out how she died was more like a modern day crime scene investigation than the informed guess-work that palaeontologists usually make do with. The team noticed that she had a broken wrist that had begun to partially heal. The injury did not kill her, but they speculate that it contributed to her premature demise.

"It might be that her mother dropped her once or that she fell down from a tree earlier in her life," Smith said. She survived the accident, but her climbing abilities would have been impaired. Unable to drink from water trapped by tree leaves, she would have had to venture down to the lake to drink. This would have proved to be a fateful decision.

The huge range of magnificently preserved fossils at Messel suggest that the volcanic lake was a death trap. Scientists believe that it sporadically let forth giant belches of poisonous volcanic gases that would have immediately suffocated anything in, around and even over the water. Ida would then have fallen into the water and been preserved in the sediment deep at the bottom.

• Atlantic productions' programme, Uncovering Our Earliest Ancestor: The Link, will be broadcast in the UK on Tuesday, 26 May at 9pm on BBC1 ( Colin Tudge's book, The Link, is published on 20 May by Little Brown.