Elephant "Missing Link" Fossil Found, Study Says

Nicholas Bakalar
for National Geographic News

October 31, 2006

Parts of a fossil jawbone discovered by a farmer in Eritrea might belong to a "missing link" species that connects modern elephants to their ancient ancestors.

The lower jaw fragments were found in the Dogali fossil site in the eastern part of the African country (Eritrea map). They date back to about 27 million years ago.

The bones belong to an animal in the order Proboscidea—large mammals with trunks—the same order that includes living elephants.

In a paper that appears in the online early edition of Proceedings of the National Academy of Sciences, the researchers name the new species Eritreum melakeghebrekristosi.

The name is derived from the site of the find and Melake Ghebrekristos, the local farmer who brought the specimen to scientists' attention.

"Throughout Africa, there is a gap in the proboscidean record in the late Oligocene, 34 to 24 million years ago," said Jeheskel Shoshani, the lead author of the study and professor of biology at the University of Asmara in Eritrea.

(Related news: "Fossils Shed Light on Africa's 'Missing Years'" [December 3, 2003].)

"Whenever there is a gap in the record, it's significant when you find specimens from that period. These specimens date from exactly the time where there is a gap."

Tooth Conveyer Belt

The jawbone pieces were discovered with teeth in place, allowing researchers to hypothesize that the animal replaced its teeth through a process called horizontal tooth displacement—the same "conveyor belt" style seen in living elephants.

If this theory is correct, E. melakeghebrekristosi would be the earliest known proboscidean to exhibit this characteristic.

The size of the teeth is another indication of the intermediate evolutionary stage of the species.

The fossil choppers are about the same size as the teeth of paleomastodons, a related family that flourished about 35 million years ago.

But the teeth are smaller than all known gomphotheres, four-tusked proboscideans that lived between 12 and 2 million years ago, and are smaller than those of mastodons, another elephantlike group that disappeared about ten thousand years ago.

Based on the size of the jaw, the new species probably looked very much like a modern elephant, but with a shorter trunk in proportion to its body size and four tusks instead of two.

The creature stood a little over 4 feet (1.2 meters) at the shoulder, significantly smaller than present-day elephants, which average 10.5 feet (3.2 meters) tall at the shoulder.

"It is more efficient to be bigger," Shoshani said. "You have fewer enemies, and you can eat more efficiently.

"The first proboscideans were the size of dogs, and they've become larger and larger" as they have evolved, he continued.

"E. melakeghebrekristosi is intermediate in size, in physical characteristics, and by date," he said. "All these things make it a missing link."

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