Islands in time
The Gran Sabana region of Venezuela hosts over 100 table-top mountains known as tepuis. In the language of the native Pemón people, "tepui" means "house of the gods". These formations are the remains of a massive sandstone plateau that began forming around 1.8 billion years ago, when sand dunes solidified into rock. This plateau once covered the ancient granite basement of the Guiana Shield, a remnant of the supercontinent Gondwana. Over hundreds of millions of years, erosion from wind and water carved away the softer rock, leaving behind these sheer, isolated mesas with cliffs rising up to 1,000 meters (3,300 feet) from the surrounding jungle.
The summits of the tepuis are alien landscapes. Their surfaces are rocky and the soil is sandy and poor in nutrients. Constant rainfall keeps the climate cool and wet, unlike the tropical warmth at their bases. This dramatic environmental isolation, combined with their immense age, has turned each tepui into a unique evolutionary laboratory. Often compared to the Galápagos Islands, these "islands in the sky" host many endemic species—plants and animals found nowhere else on Earth. Some studies estimate that about one-third of the vegetation on the summits is endemic.
A unique biology
Life on the tepuis has adapted to the harsh, nutrient-deficient conditions in specialized ways. The environment has led to a rich variety of carnivorous plants. The marsh pitcher plant genus, Heliamphora, is famous here, with many species endemic to single mountains. These plants trap insects to supplement their diet. Other carnivorous plants include sundews (Drosera) and bladderworts (Utricularia).
The animal life is also distinct. The Roraima black frog (Oreophrynella nigra) is a pebble-like amphibian that cannot hop. When threatened, it tucks its head and limbs in and rolls away from predators down the rocky slopes. Many amphibian species live their entire lives inside the water-filled wells of bromeliads or pitcher plants, which provide moisture and attract insect prey. The isolation is so extreme that some of the giant sinkholes pocking the surfaces of tepuis, such as Sima Humboldt, contain their own distinct ecosystems with species unique to that single sinkhole. These deep shafts, formed by the collapse of underground river tunnels, are "islands within islands".