DURHAM, N.C. -- A small collection of teeth and jaw fragments sifted from the Egyptian desert has provided the earliest fossil evidence for one of the three major lines of primates.
The tiny fossils offer evidence that the ancestors of bushbabies and lorises appeared during the Eocene epoch that lasted from 55 million to 34 million years ago -- at least twice as early as previous fossils had shown. These fossils represent the oldest known “toothcombed” prosimians -- a group that also includes the lemurs of Madagascar. The other two primate groups are anthropoids (monkeys, apes and humans), and tarsiers.
The fossils were collected on a 2001 expedition led by paleontologists from the Egyptian Geological Museum and Duke University, and are described in the March 27 issue of Nature. The paper is co-authored by Erik Seiffert and Elwyn Simons of the Duke Primate Center Division of Fossil Primates and Yousry Attia of the Egyptian Geological Museum. Their research is supported by the National Science Foundation, the Leakey Foundation and the Egyptian Geological Survey and Mining Authority.
According to Seiffert, who is a graduate student in Duke’s Department of Biological Anthropology and Anatomy, the teeth provide evidence that the primates belong to two different groups -- one being a primitive bushbaby named Saharagalago, and the other a loris-like species, Karanisia. Bushbabies, which range from the size of chipmunks to opossums, are nocturnal leaping animals that now live in sub-Saharan Africa, while lorises are more gangly and slow-moving and are found in the forests of central Africa and south Asia.
A major distinguishing tooth among the finds, said Seiffert, is one tiny canine belonging to Karanisia that formed part of a “toothcomb,” used by the animals to groom one another. Such toothcombs are characteristic of this line of primates.
“The early evolutionary history of these toothcombed primates has long been the most mysterious phase of early primate evolution,” said Seiffert. “Finally, after over a century of paleontological work in Africa, fossils have been found that shed important light on this issue.”
Said Simons, who is director of the fossil division, “Researchers have gathered large numbers of Eocene prosimian fossils from around the world, but none of the most ancient of these fossils had toothcombs. The oldest toothcomb prosimians, until now, were from 17- to 20-million-year-old sites in east Africa.”
However, said Simons, comparative studies of the genes of living animals -- including animals at the Duke Primate Center -- by Yale University molecular biologist Anne Yoder had suggested that the toothcombed prosimians split off from other primates much earlier. This latest fossil find confirms that theory. Yoder extrapolated rates of genetic change in today’s animals to estimate when major primate groups branched apart.
Simons emphasized that the latest finds illustrate the highly serendipitous and labor-intensive nature of paleontology. “What's exciting about this find is that even after some thirty-nine years of searching this area, we had no idea that such creatures would be discovered,” he said. “This shows that even a slightly different level or locality in a region like the Fayum badlands can yield a different cut of the evolutionary cards.”
Simons and his colleagues have long conducted expeditions to the Fayum desert region in Egypt in search of fossil primates, but the location where the new fossils were found represents an earlier period than those previously explored. While the other extinct animals found at the site clearly establish that these fossil teeth are from the Eocene epoch, the researchers hope to soon establish a more precise date using additional lines of evidence.
The researchers hope that subsequent expeditions will reveal skull and limb bone fossils of these animals, and perhaps even evidence of lemurs on the continent of Africa. The lemurs’ place of origin constitutes another major mystery of primate evolution, they said. Somehow the living lemurs became isolated on the island of Madagascar -- where they evolved into a wide variety of species -- and may have had their beginnings as early as 66 million years ago, at the very end of the Age of Dinosaurs, according to Yoder’s studies.
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