Old Bones, New Connections

A recently unearthed fossil has scientists rethinking early hominoid evolution
Back in the Middle Miocene era some 16 to 11 million years ago, Earth was planet of the apes. Indeed, so many different hominoids roamed Africa, Europe and Asia then that scientists have had a hard time figuring out from which of these creatures we--and our cousins, the modern apes--are descended. But a recent find, an astonishingly well-preserved partial skeleton from north central Kenya, is helping them prune earlier renditions our hairy evolutionary tree. This skeleton, the most complete ever found from miocene times, is described in a paper in the August 27 issue of Science.
NORTH CENTRAL KENYA.Middle miocene sites here have yielded a wealth of fossil evidence about the evolution of early hominoids. The latest clues come from Kipsaramon, just above and to the right of the center.

Senior author Steven C. Ward of Northeastern Ohio Universities College of Medicine and project director Andrew Hill of Yale University, along with fossil hunter Boniface Kimeu and researchers from the National Museums of Kenya, found the skeleton, named KNM-TH 28860, in 1993. For a little more than 15 million years, it lay buried uphill from a large number of isolated teeth at Kipsaramon, a site in the Muruyur Formation along the northern crest of the Tugen Hills west of Lake Baringo.

The group moved the specimen in a solid block of soil to the museum, where they pulled out one by one the delicate bones: most of a lower jaw with teeth, upper incisors, bones from the arm, shoulder, collarbone, chest, wrists, fingers and spine. They determined that all of the bones came from a single male.

For six years, they continued to analyze the remains, playing a sophisticated version of the Sesame Street game "one of these things is not like the other." Initially Ward believed the new bones belonged to a middle miocene primate from Kenyapithecus, a controversial genus once thought to be an early ancestor of man and modern apes. But when the researchers took a closer look, they realized that KNM-TH 28860 actually resembled only one of the two known Kenyapithecus species, namely K. africanus and not K. wickeri. They argue in their new paper that because KNM-TH 28860 looks more like K. africanus than K. wickeri does, K. wickeri--and not KNM-TH 28860--is the odd proto-man out.

To remedy the mismatch, they have christened a new genus, Equatorius, for K. africanus and KNM-TH 28860--both of which have been found near the equator. Although this new genus is not a close relative of living apes, the researchers note that it does represent the earliest known ape to spend as much time on the ground as in the trees--a key evolutionary step that our ancestors must have also taken. Ward describes Equatorius as "an animal about the size of a big adult male baboon,...whose arms and legs were about equivalent length, with a long, flexible vertebral column and powerful grasping hands and feet." He adds that they should learn more about its behavior as they continue to study the numerous skeletal bones found.

The genus Kenyapithecus, the research group says, should apply to K. wickeri alone, which is more advanced than the Equitorius lot. This new classification has shored up Kenyapithecus' often shaky status as one of the missing links between middle miocene apes and modern man. Paleontologist Louis Leakey first discovered Kenyapithecus in 1961 at a site called Fort Ternan. He dubbed the 14 million-year old upper jaw and teeth found there K. wickeri. Four years later, he dug up additional teeth and jaw bits on Maboko Island in Lake Victoria, which he called K. africanus.

TELLTALE TEETH.Based on KNM-TH 28860's abundant and well preserved teeth, including the canines and incisors, the scientists recognized its similarities to K. africanus and differences from K. wickeri.

It was based

KNM-TH 28860
This partial skeleton, a middle miocene male hominoid from Kenya, offers clues that are helping researchers reclassify some of our earliest possible kin.
Left mandibular corpus
Left massillary central incisor (left) and right maxillary lateral incisor (right)
Right mandibular corpus fragment
Right scapula
Right clavicle (right) and left proximal humerus (left)
Right humerus with first rib attached (left) and right radius (right)
Right distal ulna (left) and right proximal ulna (right)
Lowest thoracic vertebra (left) and sternum (right)
on the sophistication of these few teeth that Leakey deemed Kenyapithecus "a very early ancestor of man himself." But later scientists questioned the connection, given the scant fossil record and other seemingly prmitive features of Kenyapithecus. Freeing the genus of its more backward kind, K. africanus, as Ward and his colleagues have done, strengthens the case that Kenyapithecus is in fact our ancient kin.

"One of the reasons for the conflicting opinions about the relationship of Kenyapithecus to the great ape and human clade was that this mixed sample was giving off mixed signals. Different things were thrown into a common pot, muddling up the real story," says co-author Jay Kelley of the University of Illinois. "Kenyapithecus' exact relationship to the origin of these later apes is still somewhat of a mystery at this point, but we think that the work reported in our paper at lest establishes a clearer framework for interpreting how Kenyapithecus might fit into ape and human ancestry."

More support for K. wickeri's ties to modern apes comes from a site called Pasalar in Turkey. It turns out that K. wickeri's dental pattern bears striking similarities to an as yet unclassified 14 million year-old fossil found there, suggesting that Kenyapithecus was one of the few apes that radiated out of Africa early on to other continents. The bones from Pasalar are under further analysis in hopes of clarifying their link to K. wickeri. "The fact that Kenyapithecus can be definitely shown to be more a derived ape with possible affinities to fossils in Turkey opens the door to interesting discussions concerning the ancestry of great apes and humans," Ward comments.

Interesting, for sure. Although Ward and his colleagues put forth a compelling case, not everyone is sold on the idea that Kenyapithecus likely took the first steps out of Africa. David Begun of the University of Toronto calls the new paper extremely important, but guesses that a more prmitive ape along the lines of Equatorius may have made the initial move. He is now preparing a report on a 16 million year-old German fossil ape called Griphopithecus that looks an awful lot like Equatorius. Only more time--or more bones--will tell.

Share this Article:


You must sign in or register as a member to submit a comment.
Scientific American MIND iPad

Give a Gift & Get a Gift - Free!

Give a 1 year subscription as low as $14.99

Subscribe Now >>


Email this Article