Darwinius

Darwinius is a genus of extinct Adapiformes, a group of basal or stem group primates from the Eocene epoch, 47 million years ago (Lutetian stage) based on dating of the fossil site. The genus name, Darwinius, was named to celebrate Charles Darwin on his bicentenary and the species name, masillae, honors the Messel pit, where the specimen was found. ) The only known fossil, dubbed Ida, was discovered in 1983 at the Messel pit, a disused shale quarry noted for its astonishing fossil preservation, near the village of Messel, about 35 kilometers (22 mi) southeast of Frankfurt am Main. The fossil, divided into a positive and negative slab after the amateur excavation and sold separately, was not reassembled until 2006. The fossil is of a juvenile female, approximately 58 cm (23 in) overall length, with the head and body length excluding the tail being about 24 cm (9.4 in). It is estimated that Ida died at about 80–85% of her projected adult body and limb length.

The scientists who published the initial paper on Darwinius described it as a significant transitional form 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.

Taxonomy
Franzen et al. (2009) place the Darwinius genus in the Cercamoniinae subfamily of the Notharctidae family within the extinct Adapiformes suborder of early primates. Darwinius masillae is the third primate species to be discovered at the Messel locality that belongs to the cercamoniine adapiforms, in addition to Europolemur koenigswaldi and Europolemur kelleri. Darwinius masillae is similar but not directly related to Godinotia neglecta from Geiseltal.

The adapiforms are known from the fossil record only, and it is unclear whether they form a suborder proper, or a paraphyletic grouping. They are usually grouped under the Strepsirrhini semiorder and would as such not be ancestral to the Haplorrhini semiorder.

Franzen et al. in their 2009 paper place Darwinius in the "Adapoidea group of early primates representative of early haplorhine diversification". This means that according to these authors, the adapiforms would not be entirely within the Strepsirrhini lineage as hitherto assumed but qualify as a "missing link" between Strepsirrhini and Haplorrhini.

Older fossils are thought to represent the earliest anthropoids or the related tarsidae, and most experts hold that anthropoids evolved from tarsidae, while a smaller group agrees with Dr Hurum that the first anthropoids were adapidae, ancestral lemurs. The view of paleontologist Tim White is that Darwinius is unlikely to end the argument.

The Adapiformes, including Darwinius, clearly post-date the phylogenetic separation of primates and non-primate Eucharonta such as the colugos, and therefore cannot be considered a missing link between primates and non-primates. This separation took place in the Cretaceous, over 60 million years ago, during the diversification of the Plesiadapiformes order.

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 animal is about 58 cm from noe to tail, or roughly the size of a small, long-tailed cat.

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 lemur-like primates and the monkeys, including 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 events regarding the original unearthing of the fossil are not clear, though some facts are known. It was found in the Messel pit in 1983, after the pit had been closed to amateur fossil hunters in preparation for using the site as a landfill. The fossil came as a slab and partial counter slab, and expertly prepared by encasing them in resin. The slab and counter slab did at some point go their separate ways. The counter slab had at some point been incorporated in a composite of fabricated parts to represent a complete specimen, and found its way to a private Wyoming museum in 1991. Analysis by Jens Franzen of the Natural History Museum of Basel, Switzerland revealed that the mixed actual and faked nature of the slab. Comparing the two slabs indicate the forger had access to the whole fossil.

The primary slab remained in Germany, in the possession of a collector. The significance of the fossil was first recognized by vertebrate palaeontologist Jørn Hurum, who was shown photographs of 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. Dr. Hurum sought to find a natural history museum able to pay for the specimen, and eventually secured funds from the Natural History Museum of Oslo.

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 paleontologists Dr. Jens Franzen and Dr. Jörg Habersetzer of the Senckenberg Museum’s Research Institute. Negotiations were put in place for a book and with various broadcasters for documentary programs, all of whom agreed to keep the project secret. A deal went through in the summer of 2008 with The History Channel which has been reported as paying more for this than any other documentary.

On May 19, 2009, the team revealed their findings to the world at a press conference, and simultaneously in a paper published online in PLoS ONE, the open access journal of the Public Library of Science (officially published in print on May 21, 2009). The fossil was described as the missing link in human evolution that had long been sought by paleontologists, although some questioned this assertion. Brian Switek, an ecology and evolution university student and blogger, described that the fossil was spectacularly complete and "the first time a fossil primate has been found exhibiting such extraordinary preservation,", but also 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, that is the "higher primates" infraorder grouping all monkeys and apes.

Publicity and media coverage
thumb|250px|Digital movie of the skeleton of Darwinius. The press conference and paper on the fossil was accompanied by the launch of a website, the publication of a book which had already been distributed to bookstores, The Link: Uncovering Our Earliest Ancestors by Colin Tudge, and the announcement of a documentary (Uncovering Our Earliest Ancestor: The Link), made by Atlantic Productions in the UK, directed by Tim Walker and produced by Lucie Ridout, to be screened six days later on the History Channel (US), BBC One (UK), and various stations in Germany and Norway. The New York Daily News noted that "The unveiling of the fossil came as part of an orchestrated publicity campaign unusual for scientific discoveries." One of the paper's co-authors, paleontologist Philip D. Gingerich, told The Wall Street Journal that they had chosen to publish in PLoS as "There was a TV company involved and time pressure" and they had been pushed to finish the study.

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". Google commemorated the unveiling with a themed logo on May 20, 2009. 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."

Criticism
Independent experts have raised concern about publicity exaggerating the importance of the find before information was available for scrutiny. Paleoanthropologist Elwyn Simons of Duke University stated that is was a wonderful specimen but most of the information had been previously known, and paleoanthropologist Peter Brown of the said that the paper had insufficient evidence that Darwinius was the ancestral anthropoid. Others have also criticized claims that the fossil represents the "missing link in human evolution", arguing that there is no such thing unless evolution is visualized as a chain as there are an infinite number of missing branches, and that while the fossil is a primate, there is no evidence to suggest that its species is a direct ancestor of humans.

The authors of the paper describing Darwinius have themselves expressed dissatisfaction with the media campaign. Phil Gingerich, one of the scientists who studied the "Ida" fossil, was quoted in The Australian, saying that there was "a TV company involved and time pressure." He said that the authors were "pushed" to rush the paper to press. "It’s not how I like to do science," Gingerich concluded. Others have disagreed with this.