Paleontologists sifting through mounds of Egyptian desert sand have unearthed tiny 40-million-year-old fossil fragments that double the suspected age of one of the three major lines of primates -- and fuel the debate over the time and place of human origins.
The unexpected discovery of pieces of well-preserved teeth and jawbone from forbears of the modern-day bush baby and an extinct, loris-like creature that inhabited Earth some 20 million years earlier than scientists had thought, provides significant clues about the early evolution of omnivorous mammals, researchers said.
The oldest known remnants of this branch of the mammalian family tree -- whose sparse fossil record has left much to speculation -- could uproot some conventional ideas about when and where primates got their start, investigators said.
"We've all been waiting for this sort of discovery," said Elwyn Simons, professor of biological anthropology and anatomy at Duke University in Durham, N.C., who has led fossil-hunting expeditions in Egypt for more than 40 years.
Simons heads the division of fossil primates at the Duke Primate Center, a renowned facility dedicated to the study and conservation of bush babies, lorises and lemurs.
Collectively known as prosimians, or primitive primates, these mouse-to-cat-sized creatures -- which share an affinity for arboreal nighttime living -- comprise one of the three major primate groups. The other two are anthropoids, which include monkeys, apes and humans, and tarsiers, small, nocturnal tree dwellers with long, thin tails and large eyes that inhabit Indonesia and the Philippines in dwindling numbers.
The collection of telling remnants of past life -- sieved out of thick layers of wind-swept sand on the eastern edge of the Sahara, the world's largest desert -- bespeaks the existence of the ancestors of bush babies and lorises during the Eocene epoch, scientists said. The period lasted from 55 million to 34 million years ago.
Researchers estimate the fossils' age at between 36.9 million and 41.2 million years, at least twice the age of the previously oldest found remains of their kind. Those had been retrieved from sites in Kenya and Uganda that date back 17 million to 20 million years.
"This is a major discovery," Robert Martin, professor, provost and vice president of academic affairs at The Field Museum in Chicago, told United Press International. "However (it seems) unlikely that we have found the oldest bush babies and lorises that ever existed."
The findings, which will be reported in the March 27 issue of the British journal Nature, support the results of genetic experiments conducted by Yale University molecular biologist Anne Yoder.
Until now, the fossil record seemed to contradict her conclusions -- which were analyzed by Martin in Nature -- that placed the bush baby and loris groups in the early Eocene epoch.
The team from Duke and the Egyptian Geological Museum in Cairo discovered two tiny teeth from a primitive bush baby, called Saharagalago, meaning "desert bush baby," and a handful of jaw and tooth fragments from a now-extinct loris-like primate, dubbed Karanisia after the ancient Karanis ruins near the excavation site.
"This is a major breakthrough for our understanding of early primate evolution because ... until now, fossils documenting this group's early evolution were totally missing," lead study author Erik Seiffert of Duke told UPI. "Finally, after over a century of paleontological work in Africa, we've found them."
The fossils include fragments of a toothcomb, an unusual array of six narrow teeth at the front of the lower jaw used for grooming fur and scooping up such plant food as fruit pulp and tree gum. The prehistoric teeth bear a remarkable resemblance to those of modern-day animals.
"When we found the teeth of Saharagalago, I was shocked. They could barely be distinguished from the living bush babies," Seiffert recalled. "This suggests that in at least one aspect of their lifestyle -- their diet -- the smaller living bush babies may not be much different from their 40 million-year-old ancestors."
Named for their plaintive, infant-imitating cries and fluffy, wide-eyed cuteness, bush babies spend much of their time grooming one another with their front teeth. Fast, agile and accurate, they use their acute night vision and bat-like ears to snatch beetles, ants, termites, snails, butterflies, moths and other favored snacks after dark. Tucking their arms and legs in mid-flight for optimal speed, they easily can cover 10 yards in seconds. Their luxuriant tail, longer than their head-to-toe stretch, provides additional power for catching prey in mid-air, escaping enemies or circumventing obstacles as they romp around the rainforests and woodland savannas of sub-Saharan Africa.
In contrast, the tail-less lorises are as slow and cautious as bear cubs. Firmly gripping branches with their extremities, they wend their way, hand-over-hand, through the lush tropical forests of Southeast Asia and western Indochina.
Their name derived from the Dutch for "clown." lorises often pose in comical postures and will freeze motionless for hours. Their bodies are wrapped in thick ash-gray to reddish-brown fur and their enormous, round eyes are ringed with dark circles. Lorises present cryptic lonely figures as they forage alone through the night, while daytime finds them sheltered in hollow trees, in crevices of limbs or on branches, sleeping with head tucked between the arms.
Hoping to dig up details on the animals' past from nature's diary engraved in sediment, the investigators began excavating at a site in the Fayum region southwest of Cairo.
"The fossil locality was found in 2000, but because the area is covered with a thick layer of loose, wind-blown sand, during the first field season, we only found large jaw and limb bone fragments of primitive elephant relatives, large carnivorous mammals and crocodiles that happened to be exposed on the surface," Seiffert recalled.
"It seemed highly unlikely that we would ever find small mammals such as bush babies, but at the very end of the season I was in the process of excavating a crocodile arm bone when I found a tiny fossilized inner ear bone of a rodent lodged beneath it."
The promise of finding fossil remains of other small land mammals enticed Simon and Seiffert to return the following season with thin mesh screens to sift through the sand for tiny treasures.
"Some of our colleagues thought that we were crazy to even bother with screening," Seiffert told UPI, "but the site was of such a unique age that we wanted to go to whatever lengths were necessary to find small mammals such as primates."
Half an hour into their first day in the field, they hit pay dirt.
"It was absolutely magical," Seiffert recalled, "an unbelievable feeling to have found these new and totally unique fossil primates when such a discovery seemed so improbable."
To Martin, the new findings provide fresh evidence for his controversial assertion that the evolutionary trees of mammals and birds need to be redrawn. For example, he contends, new fossils finds, DNA analysis and statistical models suggest humans' earliest ancestors originated 90 million years ago, rather than 60 million years ago, as most scientists now think.
"The issue of times of origin is of general importance because trees based on molecular data must be calibrated using dates derived from the fossil record," he told UPI. "If those calibration dates are underestimates (because they are directly based on the earliest known representative in a poorly documented fossil record), this will have spin-off implications throughout the primate tree."
For example, Martin questions the widely accepted date of 5 million years ago for the split between chimpanzees and humans because, he contends, it is based on such suspect calibration. He is convinced the two species separated much earlier.
With the dates of their origins pushed back, continental drift becomes more relevant in determining where primates arose and how they dispersed, said Martin, who analyzed the current findings in an accompanying commentary.
"One possibility is that the strepsirrhine primates originally inhabited Indo-Madagascar, rather than Africa, and that lemurs became isolated when Madagascar separated from India," Martin said. "Subsequently, lorises could have migrated to Africa after India collided with Asia."
"Given available fossil evidence," he said, "I actually think that the most likely place of origin for primates is Asia, not Africa or India."