"Lost World" Mesas Showcase South America's Evolution
for National Geographic News
|February 20, 2004|
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 realand 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 formationsand 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 RoraimaGuyana's tallest tepui.
The massive mountainabout 9 miles (14 kilometers) long and 3 miles (5 kilometers) widelies 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.
"The tops of [tepuis] used to be a contiguous landform," Means said of the flat summits that range from a few square miles to dozens and even hundreds of square miles. This geological history means that the closest relatives to plants and animals atop one tepui are likely those found on a neighboring mountain.
"But they have been separated for a very long time," Means said. "Each summit has [its] own unique plants and animals that have evolved just to that tepui summit, depending on how long they've been isolated from each other. Yet they came from ancestors that gave rise to those found on adjacent summits."
Altitude is a major factor in the development of flora and fauna. This is especially true in the tropics, where there is a much greater diversion of species over a range of altitude.
"In the tropics species become narrowly adapted to the climate that they experience daily," Means said. "If you go up a few thousand feet, if the temperature changes by even five degrees, the animal forms found lower down can't tolerate that; they can't migrate into that because they haven't experienced it."
As a result, the tepuis are home to a large biodiversity, which became apparent to the National Geographic team from the outset.
"We began at a base of maybe 2,800 feet (853 meters) and went all the way to over 9,000 feet (2, 743 meters)," Means said. "We had camps all the way up and it was amazing. At every step the faunathe frogs we found there for examplewere totally different."
Rivas said that the team saw dramatic differences in diversity even on top of the tepuis. For example, he said he observed flowering plants within a sinkhole hundreds of feet deep atop Roraima's neighbor, Mount Weiassipu.
"The sinkhole is even more isolated than the top itself," Rivas said. "The plants on top of the tepui that had flowers were in reproduction period, but those in the sinkhole had no flowers at the time. So you could see genetic isolation between the plants even though they are physically so close."
Field Open for Future Discovery
The expedition was able only to scratch the surface of the enormous diversity on and around the tepuis. Some creatures that were collected were initially thought to be new to science but turned out to be already named. Still, the team did find interesting plants and animals along the routes up Weiassipu and Roraimaincluding the sheer rock face, or prow, of Mount Roraima.
"Virtually no scientific work has been done on the wall," Rivas said. "We did collect some interesting animals, spiders, scorpionsall kinds of creepy crawlies. I'm more an expert in frogs and snakes, not an entomologist, but I would be extremely surprised if they are not new to science. These things have a short distributionthey don't move around much."
Rivas was disappointed that the team did not have more time to explore and sample the staggering biodiversity that they witnessed. The potential for discovery remains wide open.
"A few people have been there, but really not a lot, considering what they areamong the oldest formations in the world," Rivas said. "They are like a place where time stopped. In the fauna you can see South America evolving for the last 300 million years. Understanding the diversity and the way things were dispersed from these locations is key to understanding South American biogeography."
Means hopes to be able to return to the tepuis.
"It's one of the few places left in the world where biologists have only sparingly made forays. It's a field man's dream," he said.
Read National Geographic Traveler's take on tepuis.
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