Darwinius

Darwinius masillae is a basal or stem group primate species from the Eocene epoch, 47 million years ago (Lutetian stage). The genus Darwinius, was named to celebrate Charles Darwin on his bicentenary and the species name, masillae honors Messel where the specimen was found. ) The only known fossil, dubbed Ida, was discovered in 1983 at the Messel pit, a disused shale quarry near the village of Messel, about 35 kilometres (22 mi) southeast of Frankfurt am Main. The fossil, divided in two sections after the amateur excavation and sold separately, was not reassembled until 2006.

The scientists who published the initial paper on Darwinius described it as a significant transitional form ("missing link") between early primitive primates and the later prosimian and simian lineages. The creature appeared superficially similar to a modern lemur. The fossil is classified as lying near the separation of two major primate clades: one leading to the prosimians, the other to the anthropoid monkeys and, eventually, to the great apes, including Homo sapiens. However, concerns have been raised about the claims made about its relative importance, and the publicising of the fossil before adequate information was available for scrutiny by other scientists. Another concern is that while other evolutionary steps have many more examples, this species is currently known only from a single fossil specimen.

The authors of the paper describing Darwinius classified it as a member of the primate family Notharctidae, subfamily Cercamoniinae.

Type specimen
The type specimen is a 95%-complete fossil, missing only its left rear leg. It has been named Ida after the daughter of Dr Jørn Hurum, the Norwegian vertebrate paleontologist from the Natural History Museum, University of Oslo, who secured one section of the fossil from an anonymous owner, and led the research. In addition to the bones, an imprint of Ida's soft tissue and fur outline is present, along with remnants of her last meal of fruit and leaves.

The fossil is placed within the primate family tree along with other fossil primates. Ida was originally thought to be a primitive lemur, but comparative tests revealed her to have anthropoid features. This indicates that she is a transitional fossil between primitive primates and the human lineage. Two of the key anatomical features found in lemurs are not present in the fossil: a grooming claw on the foot and a fused row of teeth, a toothcomb, in the bottom jaw. Instead, she has a short face with forward facing eyes like humans as opposed to the long face of a lemur, nails instead of claws, and teeth similar to those of monkeys. The fossil's hands have five fingers and exhibit human-like opposable thumbs. These would have provided a "precision grip" which, for Ida, was useful for climbing and gathering fruit. Ida also had flexible arms and relatively short limbs.

Digital reconstructions of Ida's teeth reveal that she has unerupted molars in her jaw, indicating that she was about 8 months old, or the equivalent of a 9 year old human. The shape of Ida's teeth provides clues as to her diet; jagged molars would have allowed her to slice food, suggesting that she was a leaf and seed eater. This is confirmed by the remarkable preservation of her gut content. Furthermore the lack of a baculum (penis bone) means that the fossil was most likely female. X-rays performed on Ida revealed that her left wrist was healing from a fracture, which may have contributed to her death. The scientists speculate she was overcome by carbon dioxide fumes whilst drinking from the Messel lake. Hampered by her broken wrist, she slipped into unconsciousness, was washed into the lake and sank to the bottom, where unique fossilisation conditions preserved her for 47 million years.

Discovery and publication
The significance of the fossil was first recognised by vertebrate palaeontologist Hurum who uncovered the specimen through a chance encounter at the Hamburg Fossil and Mineral Fair in 2006, where a dealer offered the fossil for $1 million. It had been discovered 23 years earlier by a fossil hunter and remained in a private collection. Hurum purchased the specimen for his museum based on photographs alone.

After its rediscovery it was studied in secret for two years by a team of scientists; Hurum was joined by primate evolution expert Professor Philip Gingerich of the University of Michigan, and palaeontologists Dr. Jens Franzen and Dr. Jörg Habersetzer of the Senckenberg Museum's Research Institute.

On May 19, 2009, they revealed their findings to the world in a paper published in PLoS ONE, the open access journal of the Public Library of Science. The fossil was described as the "missing link" in human evolution which had long been sought by paleontologists, although some questioned this assertion. Brian Switek, while describing the fossil as spectacularly complete and "the first time a fossil primate has been found exhibiting such extraordinary preservation," deplores the sensationalist coverage and a lack of adequate research in the published paper to back claims that it is an ancestor of the earliest anthropoids.

Publicity and media coverage
The paper on the fossil was accompanied by a documentary (Uncovering Our Earliest Ancestor: The Link), made by Atlantic Productions in the UK, to be screened on the History Channel (US) and BBC One (UK) - directed by Tim Walker and produced by Lucie Ridout. A book The Link: Uncovering Our Earliest Ancestors by Colin Tudge and a website, were also launched to explain the significance of the fossil to a broader audience. The New York Daily News noted that "The unveiling of the fossil came as part of an orchestrated publicity campaign unusual for scientific discoveries."

At the time its discovery was announced in the scientific and the popular press, the fossil was characterized as the "most complete fossil primate ever discovered"; Sir David Attenborough has described it as "extraordinary".

Independent experts have raised concern about publicity exaggerating the importance of the find before information was available for scrutiny. Others have also criticized claims that the fossil represents a missing link in human evolution, arguing that there are several missing links in human evolution and that while the fossil is a primate, there is no evidence to suggest that it is a direct ancestor of humans. During a ceremony at the American Museum of Natural History Hurum said that "This specimen is like finding the Lost Ark for archeologists" and "It is the scientific equivalent of the Holy Grail. This fossil will probably be the one that will be pictured in all textbooks for the next 100 years." Google commemorated the discovery with a themed logo for May 20, 2009.