"Lost World" Mesas Showcase South America's Evolution

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"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 fauna—the frogs we found there for example—were 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 Roraima—including 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, scorpions—all 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 distribution—they 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 are—among 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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