Why are we asking this now?
The fossil, nicknamed "Ida", was discovered in 1983 but the scientific paper describing it has only just been published amid great secrecy to coincide with the commercial launch of a popular science book and a television documentary. The creature in question has been named Darwinius masillae in honour of Charles Darwin and it lived 47 million years ago.
It is the most complete fossils of any member of the primate group of animals, which include lorises, lemurs, monkeys, apes and of course Man. The skeleton is almost perfectly preserved, clearly showing anatomical details that mark the animal out as a member of the group of animals that were part of the transition from the prosimians, such as the lemurs, to anthropoids, such as apes and humans. It is for this reason that the people behind the discovery and its publicity have called the fossil "the link" between the very first primates and the lineage that eventually led to Homo sapiens.
What is so special about the fossil?
There are several features that make Ida stand out, other than the almost miraculous preservation of about 95 per cent of its skeleton. The first striking anatomical feature – other than the absence of a penis bone or bacculum, making Ida unmistakably female – is the animal's opposable thumbs, which she used for climbing trees and picking up items of food such as berries and fruit. Opposable thumbs on a five-digit hand are a signature feature of monkeys and apes and were essential for the precision grip needed to make and handle tools, a key development in human evolution.
What else have we learnt about her?
Other anatomical features include the presence of a distinctive ankle "talus" bone in Ida's foot, another link to human anatomy. Only the human talus is obviously bigger, according the Natural History Museum at the University of Oslo, which was involved in the scientific analysis of the fossil. Further interesting features of its anatomy are the absence of a "toothcomb", a fused row of teeth in the middle of the lower jaw, and a "toilet claw", a grooming claw on the second digit of the foot. These features are attributes of lemurs but absent in monkeys and apes, indicating Ida's transition to anthropoid primates.
Furthermore, Ida's fingertips end in nails rather than claws, which is another link with monkeys and apes. Her eye sockets housed large, forward-pointing eyes that probably gave her good 3-D, binocular vision. Her big eyes would have been useful for a lifestyle of night-time foraging.
How big was she and how old?
She was about 3ft long from head to tail and her adult teeth were in the process of pushing out her milk teeth when she died. Scientists said she was about nine months old and was at that vulnerable stage of life when she was not yet fully grown but no longer requiring constant maternal care. The Oslo University scientist who studied her, Jorn Hurum, said that she was probably at the same developmental stage as his six- year-old daughter called Ida – hence the name.
X-rays and other scans also showed that Ida had a fractured wrist bone that was in the process of healing. This may have contributed to her death as it would have made her less agile than if her wrists were uninjured. The fossil is so perfectly preserved that it even shows the contents of Ida's stomach – her last meal was berries and leaves. Even the distinct impression of her fur coat can be seen around the skeleton.
What sort of world did Ida live in?
The epoch she lived in was known as the Eocene, which began about 55 million years ago, about 10 million years after the extinction of the dinosaurs. It was during the period that the warm-blooded mammals continued their evolutionary transition from small, shrew-like creatures that lived alongside the dinosaurs to the large and diverse array of animals we see today, from rats, sheep and elephants to dolphins, bats and humans.
The place where Ida lived was a semi-tropical forest near a volcanic lake in a region that became a disused pit called Grube Messel near Darmstadt in Germany. The Messel pit has yielded a rich assortment of Eocene animals, such as fish, birds, bats, turtles and dwarf horses, many of which may have died from the poison gases given off from the lake.
Who discovered her?
An unnamed fossil collected found her in the Messel pit by splitting apart a slab of rock at the base of a place called Turtle Hill to reveal two mirror-image impressions in the rock, known as the part and counterpart. The less detailed counterpart was subsequently sold to a dinosaur museum in Wyoming in America but an analysis revealed that parts of the impression had been tinkered with to make the fossil seem more complete than it was.
Then what happened?
The detailed "part" of the fossil was kept hidden until it was eventually sold in 2007 to the Natural History Museum in Oslo. It is by studying this section that scientists realised the fossil's significance in the early evolution of the primates.
Are there any doubts about the significance of the find?
The Oslo scientists have run an exhaustive set of tests on the fossil and have concluded that it is completely genuine and authentic, according to their scientific paper. But one of the slightly suspicious aspects of the story is how it has emerged in a blaze of publicity co-ordinated by the television documentary company that was given access to the scientists, along with the involvement of a publisher with a book to sell on the subject.
What's unusual about that?
Usually, new discoveries of this significance is first published in the peer-reviewed scientific literature where the claims are meticulously analysed by teams of experts.
However, this study was published in a free-access, on-line journal called PLOS which said that it announced the study to coincide with a press conference in New York organised by the American Museum of Natural History and its media partners. Rather than being in control of when the announcement should be made, which is what journals like Science and Nature usually insist on, PLOS was in the hands of other, more media-savvy organisations that could manipulate the spin and the hype.
So is Ida the missing link?
No, she is not "the link" because there is never going to be one missing link between humans and their primate ancestors. Neither is Ida our direct ancestor. She belonged to a branch that evolved in parallel to the ancestral line of primates that eventually gave rise to humans.
Ida is an important and fascinating discovery at the roots of the primate lineage but unfortunately it could become mired in hype and exaggerated claims – such as Ida being "our earliest ancestor". She was not "the link", but simply one of many, many links in the long and complicated descent of man.
Are the claims for Ida's significance overstated?
* She is not the missing link but one of many links in the long chain of Man's descent.
* The publicity statements were hyped to make her appear more special than she is.
* She was not on the direct line of descent that led to Homo sapiens but a side branch.
* It is the first time such a well-preserved primate fossil has been revealed.
* Her features clearly show the transition from lemur-like animal to ape-like primate.
* It is remarkable that such an old and important fossil has survived so well.