Darwinius

Darwinius masillae Temporal range: Mid Eocene
File:Darwinius masillae.jpg
Left and right (reversed) side of the Darwinius masillae holotype fossil
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Eutheria
Superorder:	Euarchontoglires
Order:	Primates
Genus:	Darwinius
Species:	D. masillae
Binomial name
Darwinius masillae

Darwinius masillae ("Charles Darwin's creature from the Messel pit") is a basal or stem group primate from the Eocene, known from a fossil recovered in the 1980s from 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 2007.

D. masillae is an extinct species of primate that lived 47 million years ago. It is significant as a so-called "transitional form" between the prosimians (lemurs and other primitive primates) and the simians (monkeys, apes and humans). The creature looked like a lemur but had opposable thumbs. The fossil lies near the separation of two major primate clades, one leading to the prosimians, the other to monkeys and, eventually, to the great apes including Homo sapiens.

At the time it was widely published, in the scientific and the popular press, the fossil was characterized as the "most complete fossil primate ever discovered"; it is missing only its left rear leg. Remnants of a last meal, of fruit and leaves, can be detected, and imprints of the creature's fur.

Type specimen

Radiographs of the Darwinius fossil.

The type specimen, a 95%-complete fossil, has been named Ida. In addition to the bones, an imprint of her soft tissue and fur outline is present, along with her last meal. Sir David Attenborough has described it as "an extraordinary fossil." Ida lived in the early Middle Eocene during a period in evolutionary history after the extinction of the dinosaurs, when mammals first began to thrive on the planet. In primate evolution, the anthropoids (monkeys, apes and humans), split from the branch leading to modern prosimians (lemurs, lorises and tarsiers).

Scientists have worked to identify the fossil and place it 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, a grooming claw on the foot and a fused row of teeth, a toothcomb, in the bottom jaw, are not present on the fossil. 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 9 months old, or the equivalent of a 6 years 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 definitely female.

X-rays reveal that her left wrist was healing from a bad fracture, which may have contributed to her death. The scientists believe 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 until discovery.

Discovery and publicity

The significance of the fossil was first recognised by vertebrate palaeontologist Dr Jørn Hurum from the Natural History Museum, University of Oslo, who uncovered the specimen through a chance encounter at the Hamburg Fossil and Mineral Fair, Germany, in 2006. It had been discovered 25 years earlier by an amateur fossil hunter, but remained hidden from the world in a private collection. Hurum acquired the specimen for his museum, allowing it to be scientifically studied for the first time.

Since its rediscovery it has been 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. They revealed their findings to the world in a paper published on 19th May 2009 in PLoS ONE, the open source journal of the Public Library of Science.

The paper 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 (Little Brown, 2009) and a website, http://www.revealingthelink.com, were also launched to explain the significance of the fossil to a broader audience.

External links

• http://www.revealingthelink.com/, the website for the documentary about the type specimen