Missing Link

Feast your eyes on what a group of scientists call the Holy Grail of human evolution.

A team of researchers Tuesday unveiled an almost perfectly intact fossil of a 47 million-year-old primate they say represents the long-sought missing link between humans and apes.

Officially known as Darwinius masillae, the fossil of the lemur-like creature dubbed Ida shows it had opposable thumbs like humans and fingernails instead of claws.

Scientists say the cat-sized animal's hind legs offer evidence of evolutionary changes that led to primates standing upright - a breakthrough that could finally confirm Charles Darwin's theory of evolution.

"This specimen is like finding the Lost Ark for archeologists," lead scientist Jorn Hurum said at a ceremony at the American Museum of Natural History.

"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."

A team of amateur fossil hunters discovered the near-perfect remains inside a mile-wide crater outside of Frankfurt in 1983.

Experts believe the pit was a volcanic caldera where scores of animals from the Eocene epoch were killed and their remains were kept remarkably well-preserved.

Though the pit has been a bountiful source of other fossils, the inexperienced archeologists didn't realize the value of their find.

Years later, the University of Oslo bought the 95%-intact fossil, and Hurum studied it in secret for two years.

His colleague, Jens Franzen, hailed the discovery as "the eighth wonder of the world."

"We're not dealing with our grand, grand, grandmother, but perhaps with our grand, grand, grand aunt," Franzen said.

The unveiling of the fossil came as part of a carefully-orchestrated publicity campaign unusual for scientific discoveries.

The type specimen, a 95%-complete fossil, has been named "Ida" after the daughter of Jørn Hurum, the Norwegian paleontologist 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. 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"; it is missing only its left rear leg. 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.
Radiographs of the Darwinius holotype fossil.

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 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.

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 where a dealer offered the fossil for $1 million. It had been discovered 23 years earlier by an amateur fossil hunter, but remained hidden from the world in a private collection. Hurum acquired the specimen for his museum based on photographs alone, allowing it to be seen and 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 19 May 2009 in PLoS ONE, the open access journal of the Public Library of Science.

The paper regarding the findings of the fossil was also 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.

Independent experts have raised concern about publicity exaggerating the importance of the find before information was available for scrutiny News coverage has described the discovery as "the missing link in human evolution" and the "eighth wonder of the world" which "finally confirms Charles Darwin's theory of evolution." Science historian John Wilkins has commented that there is no missing link, which is an outdated concept dating back to the great chain of being; instead, there are an infinite number of missing branches in Darwin's metaphor of the tree of life. 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.

The Messel Pit site has been described as an Eocene 'Noah's Ark' and is home to some of the world's most remarkable fossils, including entirely intact, fully articulated mammals. The fossils offer an astonishing glimpse into a 47 million year old ecological community. Typically the intact fossils are in a relaxed position, indicating that, like Ida, they were anesthetized by a burst of carbon dioxide from the Messel lake before they drowned. This incredible menagerie of fossils helps us understand and visualise the early relatives of today's animals.

Very early forms of horses, bats, birds, gars and turtles have all been found in the Messel Pit. Despite being separated by 47 million years of evolution, they would not look out of place in a modern zoo. Others are far less familiar - they have either become extinct or evolved beyond recognition.
Hyracotherium


Some of the most famous inhabitants of Messel are the primitive horses; some sixty nearly complete specimens have been recovered. They are the earlierst known ancestors of modern horses. However, even the smallest of today's horses would tower over their Messel counterparts, which averaged just 20 cm in height. The early horses are believed to have been browsing herbivores that fed on leaves and fruit.
Atractosteus strausi


The gars are a primitive fish group who survive to this day, often referred to as 'living fossils'. Outwardly, the Messel gars look scarcely different from their modern counterparts. Their massive skulls have a protruding crocodile-like snout, and a set of viciously sharp teeth. Their tough scales provided an effective coat of armour.
Palaeochiropteryx tupaidon


Bats are the most commonly found mammal group at Messel, and so far eight species have been identified. The delicate build and broad wings of the Palaeochiropteryx species indicate they were slow but agile fliers, and their preferred hunting ground was near to the ground or through low-hanging branches. Moths and small butterflies have been found in its gastrointestinal tract.
Unidentified Bird


The first direct ancestors of birds appeared 115 to 105 million years ago. There are at least fifty species of birds at Messel and with hundreds of skeletons found, they account for more than half of all the vertebrate fossils. The fossil above is an unidentified species.
Allaeochelys crepsesculpata


Today's turtles have hardly diverged from their Messel Pit ancestors, and have colonised virtually all continents and environments. Six species have been found at Messel, and there is even a site named after them - 'Turtle Hill'. Allaeochelys crepsesculpata was a soft-shelled turtle, closely related to the pig-nose turtle of Papua New Guinea and Australia, and fed on fruit, vegetation, worms, snails and fish.
Gastornis


This species is only known from Messel by a femur bone, but further studies revealed it was a two metre tall flightless bird, weighing over 100 kilos. Some believe it used its beak and claws to pin down and dismember its prey, although it may have been a herbivore. Gastornis were also found in Eocene North America.
Leptictidium


The Lepticidium of Messel were odd-looking creatures. They moved like kangaroos, and had good manoeuvrability and high acceleration. The short trunks on the ends of their elongated snouts were used to sniff out prey - such as lizards, insects and mouse-sized mammals.
Pristichampsus


An extinct genus of crocodyllian, Pristichampsus grew up to ten feet in length. Bizarrely it had hoof-like toes and was probably a land dweller. It was capable of galloping, and even standing on its rear hind legs. Its teeth were sharp and serrated, ideal for hunting primitive mammals.
Macrocranion tupaiodon


With the exception of bats, Macrocranion tupaiodon is the most commonly found species at Messel. Its short fur, large ears, and long hairs around the snout indicate it had well developed olfactory, tactile and auditory senses, typical of a nocturnal animal. Its powerful hind limbs indicate a fast-moving mouse-like ground dweller, able to escape from predators with a four-footed burst of speed.