New York - Scientists have announced the discovery of a 47-million-year-old human ancestor - twenty times older than most fossils that illustrate human evolution.
Discovered in the Messel Pit in Germany, the fossil - dubbed Ida - is a transitional species. It shows characteristics of both the very primitive nonhuman evolutionary line of prosimians, such as lemurs - but even more similarity to the anthropoid evolutionary line, which includes monkeys, apes and humans.
Ida, who measured around two feet in length, lived 47 million years ago, during the Eocene Epoch, a time when modern species were just starting to emerge. She was preserved in Germany's Messel Pit, a mile-wide crater of oil-rich shale, and is, astonishingly, 95 percent complete.
Two years of fossil analysis by Dr Jorn Hurum of the University of Oslo's Natural History Museum reveals that the prehistoric primate was a young female. Opposable big toes and nails rather than claws confirm that the fossil is a primate, and the presence of a talus bone in the foot links Ida directly to humans.
The fossil also features the complete soft body outline as well as the gut contents, which show that Ida ate fruits, seeds and leaves. X-rays reveal both baby and adult teeth, and the lack of a "toothcomb," which is an attribute of lemurs. The scientists estimate Ida's age when she died to be approximately nine months.
Ida was found to be lacking two of the key anatomical features found in lemurs: a grooming claw on the second digit of the foot, and a fused row of teeth in the middle of her lower jaw, known as a toothcomb. She has nails rather than the claws typical of nonanthropoid primates such as lemurs, and her teeth are similar to those of monkeys. Her forward-facing eyes are like ours, enabling her fields of vision to overlap, allowing 3D vision and an ability to judge distance.
The fossil's hands show a humanlike opposable thumb, which would have provided a precision grip. Evidence of a talus bone links Ida to us. The bone has the same shape as it does in humans today, though the human talus is obviously bigger.
X-rays reveal that a broken wrist may have contributed to Ida's death - her left wrist was healing from a bad fracture. The scientists believe she was overcome by carbon dioxide gas while she was drinking from the Messel Lake; the still waters of the lake were often covered with a low-lying blanket of the gas as a result of the volcanic forces that formed the lake and were still active. Hampered by her broken wrist, Ida may have slipped into unconsciousness and been washed into the lake, where the unique conditions preserved her for 47 million years.
Ida's story is to be published as a book, The Link, and will also be revealed in a special documentary film, also called The Link, to be screened by History on Monday at 9.00pm EDT and broadcast in over twenty countries. There's a website about Ida here.