Oldest monkey skull shakes up evolutionary tree

Southern Illinois University
Carbondale, Illinois 62901

Director Sue Davis 618-453-2276
Writer Kathryn C. Jaehnig 618-453-2276

July 23, 1997

SIU researchers: Oldest monkey skull shakes up evolutionary tree

CARBONDALE, Ill. óResearchers from Southern Illinois University have discovered the oldest African or Asian monkey skull yet found. Their account of their find appears in the July 24 issue of ìNature,î scienceís most prestigious journal.

ìThis 15-million-year-old skull is significant because it flies in the face of what scientists have believed about how the earliest monkeys looked and behaved,î said Brenda R. Benefit, an associate professor of anthropology at SIUís Carbondale campus since 1990.

ìIt also challenges commonly held beliefs about how the ancient ancestors of apesóand humansólooked. And it influences where we can place other fossil catarrhines (Old World monkeys, apes and humans) on the evolutionary tree. The concept of ancestor influences everything else down the line.î

Benefit and her husband, fellow SIUC anthropologist Monte McCrossin, found the skull in 1994 on Maboko Island in Kenyaís Lake Victoria.

ìIt surprised us because itís so different from what scientists thought that early ancestor would have looked like,î she said.

For years, those who studied monkeys and apes in Africa and Asia believed that the ancestor of them all had a round head, short face and small teeth made for eating leaves. It would most closely resemble a present-day gibbon or leaf-eating monkey, they thought.

But this ancient skull has a low braincase, long face and big teeth. It ate fruit, not leaves. And while clearly a monkey, its forehead, cheeks and eyesockets make it look more like smaller version of an orangutan.

ìIt represents an animal that lies somewhere on the evolutionary tree between modern monkeys and the ancestor that gave rise to all monkeys, apes and humans,î Benefit said.

The newly found skull also will change how scientists look at fossils of other animals. For example, because it resembles the skull from a 32-million-year-old Egyptian primate, that animal also should fit on the family tree.

ìThe Egyptian skull didnít have the round head and short face of the gibbon-like model, so one group of scientists claimed it couldnít be an ancestor of monkeys and apes; another group said it was an evolved ape,î Benefit said.

ìNow we can see that the skull of this Egyptian primate is very similar to that of the earliest monkeys. It fits right on the line that gave rise to both monkeys and apes.î

The Kenyan skull came from a monkey belonging to an ancestral family dubbed ìVictoriapithecusî for Lake Victoria, where anthropologists first unearthed its remains in 1933. This group flourished during the Miocene period, between 7 million and 23 million years ago.

Benefit has been studying this ancient family since 1982, when she did doctoral research on hundreds of their fossilized teeth. In the years since, she and her research team have uncovered some 10,000 fossils at Maboko. More than a third of those are primate fossilsó2,000 of which came from this particular group.

ìMaboko is a remarkable site for primatesóthereís just no competition,î Benefit said. ìItís the one place from which you can really reconstruct monkey evolution.î

The SIU researchers found the skull in a trench first excavated by famed anthropologist Louis Leakey in 1949.

ìWe had left the trench intact for its historical value, but people were starting to farm in that area, so we decided it no longer made sense not to dig there,î Benefit said.

ìAfter removing a layer of stone, we first found a complete crocodile skull, then a complete rhinoceros skull, then we found this one. It was just lying there, looking up at us.î

Dating techniques showed the fossilized skull was some 15 million years old. It is the oldest Old World monkey skull ever foundóand the only complete monkey or ape skull from the Miocene era.

ìYou might find a face, but the brain case would probably be broken off,î Benefit said.

ìAt about 5 million years ago, you start finding complete skulls from human ancestors, but everybody else has their brain case brokenóprobably because predators are crunching the skulls and eating the brains.î

The skull, now housed in a walk-in vault, has become part of the permanent collection of the National Museums of Kenya in Nairobi.

As for Benefit, she will return to Maboko Aug. 3 to join a crew of SIU students and Kenyan fieldworkers. There she will study new fossils collected this year.

ìWhile there are some new hand and foot bones, the story on this particular group (ëVictoriapithecusí) is really pretty much closed,î she said. ìThe new fossils just confirm what we already know.

ìWhat weíre interested in now is ëKenyapithecus,í an ape that existed at the same time. Every new fossil there is telling us something new. We think that it will be at least as significant as ëVictoriapithecusíóand perhaps even more soóbecause it actually may be an ancestor to the great apes and humans.î -30-