By William Mullen
Chicago Tribune Company
March 16, 2000
- The discovery of incredibly tiny monkeylike primates, some the
size of a human thumb, is cranking up the monumental debate over
how monkeys, humans and great apes evolved.
Paleontologists working in China have been recovering bones of
three tiny primate species that lived 42 million years ago, two
of them the smallest primates known to science, weighing one-third
and one-half ounce, respectively. The discovery may represent a
critical link between higher- and lower-order primates. And it also
could cast doubt on the long-held theory that such species arose
The ankle bones of the pint-size primates are about as big as grains
of rice. They are key evidence of the evolution of anthropoids (monkeys,
apes and humans), according to Daniel Gebo, the Northern Illinois
University anthropologist who heads the research team recovering
the bones in China.
His team is working in limestone quarries that 42 million years
ago lay under a steaming rain forest that was home to a kingdom
of Lilliputian animals, including a rhinoceros which--if alive today--might
make a dandy house pet. The primate bones are what is left of the
animals after being eaten by owls.
"Few would have predicted such a diminutive monkeylike creature
at such a key branch of evolution," Gebo said of the discovery
being chronicled Thursday in the British journal Nature.
"These are the smallest primates ever discovered, alive or
extinct," Gebo said. "Some of these fossils are one-third
the size of the living mouse lemur from Madagascar, which at one
ounce is the smallest known primate."
All three of the primates lived in the upper canopies of the primeval
rain forest trees. The largest of the three, Eosimias, a creature
weighing about 5 ounces, is particularly fascinating to scientists,
as it is the oldest anthropoid fossil ever found.
In the Nature article, Gebo's team lays out evidence that Eosimias
fills a previous gap in the fossil record, linking lower (prosimian)
and higher (anthropoid) primates. The team describes the two smaller
primate species in an article to be published in April in the Journal
of Human Evolution.
"Nobody thought a primate could get so small, so this is a
totally novel and surprising discovery. We have broken the sound
barrier of how small anthropoids could get," said L. Christopher
Beard, a paleontologist at Pittsburgh's Carnegie Museum, one of
Gebo's team members and a co-author of the articles.
Gebo's team has spent years combing through piles of nearly microscopic
bones and bone fragments found in mud and debris that filled fissures
that had opened in the limestone bed under the rain forest 42 million
years ago. The bones were a part of that debris, now being recovered
by Chinese laborers in the limestone quarry.
Using a process similar to panning for gold, Gebo and his team
sifted through the debris to recover the fossilized bones of the
small creatures that lived in the forest back then, a place similar
to the Amazon or Borneo, much hotter than today's China. In addition
to finding the primate bones, they also discovered remains of a
dozen other pint-size animals, but none of any large animals.
"It was an interesting place," said Beard. "There
were little mouselike rodents, small bats, tiny rabbits and even
an extinct rhino that was about the size of a dog."
Researchers have not found complete skeletons of Eosimias or the
smaller, unnamed primates, but the diminutive stature of the animals
tells researchers a lot about how the creatures lived and died.
"These were such amazingly small creatures," Gebo said,
"that their rate of metabolism would have had to have been
tremendously high, like hummingbirds. To compensate for loss of
body heat, they'd have to be moving about constantly and feeding
constantly on high-calorie diets, probably lots of insects and sugary
They probably were solitary, nocturnal animals that bounded about
on upper branches of the forest, he said, the perfect prey for ancient
The bones found are broken in the same way owls break bones of
their prey before swallowing them, Gebo said. Markings on the bones
bear the kind of marks left by owl digestive acids.
"Owls digest the flesh of their prey, but their stomachs form
pellets out of the fur and bones of their food, and they regurgitate
the pellets like hairballs," Gebo said. "We think our
fossil bones were in those owl pellets that somehow got washed into
the fissures of the limestone."
Gebo's team includes his wife, Marian Dagasto, a molecular researcher
at the Northwestern University Medical School; Chinese paleontologist
Qi Tao; and Beard.
Beard, in fact, found teeth and jaw bones of Eosimias in the same
Chinese quarry sites several years ago. Many fellow scientists rejected
Beard's theory that Eosimias was a primate, and because he had found
only teeth and jaw bones, he had little else to underscore his theory.
Gebo and Dagasto are experts in fossil primates--Gebo specializing
in their foot structures--so Beard subsequently asked Gebo to head
a team to look for more anatomical evidence of the early, miniature
primates. The rigors of examining thousands of fossil bones under
microscopes paid off with the identification of dozens of ankle
bones no bigger than a grain of rice, including those that confirm
Eosimias was a primate.
"These are very interesting findings," said Duke University
paleontologist Richard Kay. "It is an animal that lived in
China 45 million years ago, and the oldest identified monkeys and
apes in Africa are 37 million years old.
"There has been a big debate about where and from what continent
the monkeys and great apes originated. The traditional view has
been Africa, but there always has been doubt about that. This does
not prove they originated in Asia, but it raises the level of discussion."