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New creatures found in Ethiopian fossil deposits

Posted on: Monday, 8 December 2003, 06:00 CST

New creatures found in Ethiopian fossil deposits

Scientists get clues to evolution of mammals

By SUSANNE QUICK squick@journalsentinel.com, Journal Sentinel

Monday, December 8, 2003

While lions, tigers and bears were evolving in the Northern Hemisphere, between 24 million and 32 million years ago, an odd assortment of creatures, including primitive elephants, hyraxes and horned rhino-like species, were doing the same in the south -- or so it was assumed.

Until now, scientists didn't really know exactly what animals were evolving in Africa and Arabia, how they were evolving or what they were evolving into during this period. The Afro-Arabian fossil record was a big black hole.

But a team of scientists from the United States and France reports in the latest issue of the journal Nature that a new fossil deposit at Chilga, Ethiopia, has finally allowed a peek.

And they discovered six new species in the process: five early trunked species, or proboscideans -- elephant relatives and ancestors -- as well as a large, 5,000-pound beast called arsinoitherium.

"Eight million years is a big chunk of time," said John Kappelman, a professor of anthropology and geological sciences at the University of Texas at Austin. "You wipe out the last 8 million years of our history, and you've lost all knowledge of human evolution -- and then some."

And while the excavation has answered some questions about the evolution of African mammals, it has also sparked new inquiries for paleontologists to explore, said William Sanders, a paleontologist at the University of Michigan in Ann Arbor and a member of the research team.

"It has allowed us to see that the story of elephant evolution was not driven by Eurasian events," he said. "But we've still got a ton to figure out."

Today, apart from border stops at national boundaries, passage by land between Africa and Asia, via Arabia, can be done with ease. Camels, nomads and cars make the journey with fair regularity.

But between 24 million and 65 million years ago, Afro-Arabia was an isolated island continent, moving slowly north atop the Earth's fluid-like mantle.

Because of this isolation, the land mammals of Afro-Arabia and Eurasia never met -- evolving independently for millions of years.

Indeed, it wasn't until the Afro-Arabian continent collided with Eurasia, about 24 million years ago, that most of the African animals we think of today -- dogs, lions, hippos, antelope, gazelles and hyenas -- made their way south.

And when the continents hit, a lot of the early African mammals - - documented from a 33 million-year-old deposit in Egypt at a place called the Fayum -- disappeared.

But whether the African mammals went extinct before the Eurasian invaders came in, or whether they were outcompeted as a result of the new migrants, was not known, the scientists write in Nature.

Fauna, animals grew

The evidence from Chilga shows that large African fauna were doing just fine before the collision. At this point, they don't seem to have succumbed to changes in climate. Indeed, some creatures, such as the early elephants, were actually blossoming.

Five of the six species discovered were early proboscideans. And in terms of mammalian evolution, this marks a virtual explosion of ancestral elephants, Sanders said.

But other animals native to Africa -- such as the "collie-sized" hyraxes -- probably couldn't compete, Sanders said.

Hyraxes today are the closest living relative of elephants. Small, hairy and rodent-like, the guinea pig-size creatures clamber about rock outcroppings in sub-Saharan Africa.

But between 27 million and 33 million years ago, there were hyrax species as large as medium-sized dogs. And these ancient animals grazed on grass and leaves -- in a similar manner to today's African antelope, Sanders said.

"They (hyraxes) were eating the same foods that modern ruminants" such as gazelles, impalas and elands ate, Kappelman said. But, ruminants had the advantage of a rumen, a specialized stomach section that efficiently digests plants.

So, when the Eurasian antelope moved south, the hyraxes lost out. They just weren't as effective at browsing.

Giant rhino thrived

Another creature, called arsinoitherium, is a little more of a puzzle.

Arsinoitherium were discovered in the fossil beds of the Fayum, in Egypt. Looking a lot like a rhino -- stout in shape and with two horns projecting out and above their snouts -- they were believed to have gone the way the hyrax: outcompeted by invading rhinos.

The new evidence from Chilga, however, throws that theory into doubt.

Whereas early rhinos and Fayum arsinoitherium were about the same height and weight as one another, the arsinoitherium discovered at Chilga were humongous.

They were about five times larger than the rhino invaders -- 7 feet at shoulder height and 5,000 pounds -- so Sanders thinks it is unlikely the two mammals competed for food.

It is more likely that climate effects -- and the changing landscape -- may have smoked these archaic creatures out of existence.

"I think this find is pretty important," said Andrew Hill, professor and chair of anthropology at Yale who was not involved with the study. "I'm not sure it was all that surprising. But, it's still important."

It's just amazing to think, he said, "that in all the 30 million- square-kilometer area of Africa, there is just one site to represent a whole of 10 million years of evolution."

"There just have to be more sites out there," he said.

And Kappelman and Sanders are keeping their fingers crossed that he is right.

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