Early explorers spoke of mysterious mountains towering above South America's jungle. Such stories inspired Arthur Conan Doyle to write The Lost World, a novel set in an isolated place still inhabited by dinosaurs. The dinosaurs were fiction. But the mountains are real—and they are a link to Earth's prehistoric past.

The dramatic sandstone mesas are called tepuis. There are over a hundred of the high, remote plateaus, which thrust like rocky islands above the dense jungle foliage. Little is known about the unique plants and animals that inhabit the walls and tops of these formations—and they may yet shed much light on the evolution of South America.

The tepuis are ancient even by geological time. They are some of Earth's oldest formations.

"The sandstone rock of these formations was laid down as sediment some 1.6 billion years ago. That is more than three times older than the time of the earliest macroscopic fossils," said Bruce Means, president and executive director of the nonprofit Coastal Plains Institute and adjunct professor of biological science at Florida State University.

"I'm not a geologist," Means said, "but the geology of these tepuis figures prominently in their ecology. That's what first led me [to the tepuis] back in the late 1980s to work on evolutionary problems."

The islands of rock remind Means of a more heralded island group in the world of evolutionary study.

"I've been to the Galápagos," he said, "and these high-altitude mesas are at least as good as the Galápagos in terms of the archaeology of evolutionary activity. But they haven't been well promoted in the scientific community or in popular knowledge."

Unique Species May Abound

Some of the secrecy surrounding the tepuis can be attributed to their remoteness. Though tepuis are a source of pride and the focus of some research interest in South America, the undeveloped areas where they are found in Venezuela, Brazil, Suriname, and Guyana are not well mapped or well traveled.

On a recent exploration of the area, Means joined Jesús Rivas, a native of Venezuela and adjunct professor of biology at the University of Tennessee. Together they journeyed with National Geographic Ultimate Explorer television correspondent Mireya Mayor to Mount Roraima—Guyana's tallest tepui.

The massive mountain—about 9 miles (14 kilometers) long and 3 miles (5 kilometers) wide—lies where the borders of Guyana, Brazil, and Venezuela meet. Its wide, flat summit tops out at 9,094 feet (2,772 meters).

It's both the high altitude and the ancient age of Roraima that makes it so bio-geographically interesting.

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SOURCES AND RELATED WEB SITES Coastal Plains Institute Bruce Means Site