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ACADEMY SCIENTIST FINDS FIRST FOSSIL CHIMP
SAN FRANCISCO (August 29, 2005) - Lucy may be the most famous of the fossil hominins, but she does not stand alone in that category – over the past few decades, researchers have found thousands of fossils from our early human ancestors. Surprisingly, however, scientists had not identified a single fossil from a chimpanzee until Nina Jablonski, Curator and Irvine Chair of Anthropology at the California Academy of Sciences, identified three chimp teeth from a fossil site in Kenya ’s Rift Valley in late 2004. Her intriguing discovery will be announced in the cover story of the September 1 issue of Nature.
Jablonski describes the discovery as an example of “paleontological serendipity.” Sally McBrearty, an anthropologist from the University of Connecticut who runs the excavations at the Kapthurin Formation in the Rift Valley, had asked Jablonski to describe the monkey fossils her team had excavated during their 2004 field season. Excited by the opportunity to spend more time studying Old World monkeys, Jablonski flew out to Kenya and set up a temporary lab in the National Museums of Kenya in Nairobi , where she began sorting through fossils. When she picked up the first of the three teeth that she would eventually identify as chimp teeth, she was puzzled. The tooth looked similar to the gibbon molars she had often seen in China , but she knew that gibbons had never lived in Africa . Jablonski realized, then, that she was holding a molar from a different type of ape. After comparing the fossil to teeth from modern chimps, she knew she had a match – the morphology was unmistakably that of a chimpanzee molar. The tooth was too low-crowned and its enamel was too thin for it to have been a hominin tooth. A few weeks later, Jablonski identified another chimp tooth – an upper incisor – that probably came from the same individual. Excited by these results, McBrearty sent her team back to the site where the chimp teeth had been excavated. They soon located a third tooth – the other upper incisor. From the state of wear on the teeth, Jablonski estimates that the animal was about 7-8 years old when it died. Grooves on the teeth show that the chimp was nutritionally stressed when it was growing up, a fate that is not uncommon for chimps today.
Based on the other fossils that were found at the site, including hippopotamus, crocodile, catfish, and turtle bones, Jablonski concluded that the ancient chimp lived on the shore of a lake in a fairly wet, wooded habitat. This type of environment – the same type of environment chimps prefer today – is probably the reason that no chimp fossils had ever been found before now. Bones tend to rot away in wet habitats, so it is rare for them to remain in the fossil record in these environments. Luckily, teeth are more likely to be preserved, since tooth enamel is harder and denser than bone.
The three chimp teeth that Jablonski describes in the paper provide the first evidence that chimpanzees and ancient hominins coexisted in Africa . Modern chimps are confined to wooded West and central Africa , whereas most fossil hominin sites are found in the semi-arid East African Rift Valley, so scientists had long suspected that the two groups would not have overlapped. However, hominin fossils attributed to either Homo erectus or Homo rhodesiensis have been found at the Kapthurin Formation in the same soil layer as the newly discovered chimp fossils, proving that the two groups occupied the same area during the Middle Pleistocene. “This find suggests that for most of our history, humans have probably lived in harmony with the species that are most closely related to us,” says Jablonski.
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