In the northeast of South America, there lies a sprawling geological formation known as the Guiana Shield; an expanse of 1.7 billion year old rock. Long ago, it was a high plateau of sedimentary stone, but most of it has since been eroded away.
What remains of this ancient highland are immense blocks of sandstone, flattened at the top. The local Pemon people call them tepuis, meaning “houses of the gods”, and there are hundreds of them.
Most tepuis are scattered across Venezuela, but they extend into neighbouring Guyana and Brazil too. Outside of the Andes, these tabletop mountains are among the tallest landforms in South America.
You have Mount Roraima, the inspiration for Arthur Conan Doyle’s The Lost World:
Auyán-tepui, home to the world’s tallest waterfall:
Cerro Autana, a mountain which has a cave cutting right through it, with an opening on either side:
Sarisariñama, the surface of which is stippled with massive sinkholes:
And many more. Towering high above the forests and savannahs, surrounded by sheer cliffs on all sides, tepuis are just as remote and inaccessible as islands in the sea; they are effectively islands in the sky. And, just like marine islands, they have a unique array of wildlife which evolved in a vacuum, cut off from the “mainland”.
Before I introduce you too the flora and fauna of these mountains, I’ll go over some of their most interesting physical characteristics which make them such unique environments. Most tepuis are surrounded on all sides by abrupt vertical cliff faces.
On top, the terrain varies, but you’ll often find these otherworldly rock formations known as stone forests. Here, the elements have eroded the soluble rock into complex pavements of grooves, pillars and furrows.
Sometimes, the gouged-out depressions fill up with water, which is then colonized by colourful algae.
Erosion has created many other spectacular features on tepuis. There are innumerable caverns beneath the tabletops, most of them unexplored. As they are formed of quartzite, an incredibly hard mineral, they must have taken hundreds of millions of years to form, and may be the oldest caves on Earth.
Some of the chambers are massive (look at the size of the person in the bottom left, below), and one - Abismo Guy Collet - is the deepest cave in all of South America, at a depth of 671 metres. It’s also the world’s deepest quartzite cave.
Inside the caverns, there are subterranean lakes and rivers, bizarre rock formations, ancient microbial growths, and wildlife such as blind fish, scorpions, spiders and giant cave crickets.
When the rock above these caverns collapse, sinkholes form. There are many sinkholes pockmarking Venezuela’s tepuis, some of them measuring over 300 metres, both in diameter and depth.
Cerro Sarisariñama, a specific tepui, is particularly famous for its holes, which are themselves so isolated that there may be species at the bottom endemic to each particular sinkhole.
And then of course there are the waterfalls. When rivers spill over the edge of the mesas, they form some of the most spectacular falls on Earth. The most well-known is Angel Falls, the world’s tallest waterfall, plunging nearly a kilometre down to the lowlands below.
Other notable examples include Kukenán Falls, which isn’t quite as towering, but still extraordinarily tall at 610 metres:
And Kaieteur Falls, the world’s largest single-drop waterfall in terms of total volume:
Now, let’s take a look at the wildlife found on these sky islands. In the bare limestone pavements and stone forests, there isn’t much real estate for plant life, but a handful of hardy species eke out an existence in the cracks.
Some plant species here are only found on one particular tepui, and about a third of the total flora is endemic to the Guiana Shield. Bromeliads, close relatives of the pineapple, are especially common.
The small trees which manage to grow on the rocks, such as Bonnetia roraimae, are quite alien indeed.
The reddish colour of their leaves is due to anthocyanin pigments, which help protect them against extremes of weather. The red-brown hue of the vegetation on some tepuis can even be seen from space:
Another thing about these rocky areas is that what soil there is is very thin and poor in nutrients. As a result, some plants use an alternative source of nutrition - animals. Carnivorous flora is common here, including pitcher plants which drown insects in digestive nectar:
And sundews. Their leaves are covered in mucus-coated hairs, and when flies get stuck in the secretion, the leaf rolls up, constricting the prey and slowly digesting it.
The conditions atop tepuis are not always so unforgiving, however. Some summits feature shrublands, savannahs, and dense tropical forests.
Then there’s the animal inhabitants. Just like the plants, tepui fauna shows high levels of endemism, meaning that many species are found nowhere else. The limited space and scarcity of food mean that there aren’t any very big animals atop the plateaus, but there’s still plenty of fascinating wildlife.
Although colonist species from the lowlands probably do come in every now and then, most of the wildlife on the tepuis is likely descended from animals that were there before the surrounding land was eroded away. Their ecosystems guarded by sheer cliffs, said animals evolved in isolation from the rest of the world.
Let’s start with the endemic birds. This includes the tepui tinamou, an elusive ground-dwelling bird:
The Roraiman nightjar, which is nocturnal:
A wide variety of hummingbirds, including the tepui goldenthroat and the peacock coquette (pictured):
The tepui parrotlet, which commutes between mountaintops in flocks of several hundred:
The greater flowerpiecer, often found on the barren karst rocks, which perforates the base of flowers to access nectar:
The colourful tepui brushfinch:
And many birds in the group Tyranni, such as the Roraiman antwren:
And the striking scarlet-horned manakin, which has a pair of feathery tufts on its head (its “horns”):
While the forested foothills of the mesas are rich in mammal fauna, the challenging conditions at the top (and the inaccessibility) mean that there aren’t many mammals here. Those that are are usually quite small.
Some endemic examples include Tyler’s mouse-opossum, which I don’t think has ever been photographed (a close relative is shown):
McConnell's climbing rat (again, a closely related species is is shown below):
Isabelle’s ghost bat (again, not the exact same species in the photo):
And the prickly Roraima mouse, which was thought extinct until its rediscovery in 2009. The picture is correct this time.
What’s especially interesting about this mouse is that its closest genetic relatives are not found on the lowlands surrounding the tepuis, but way over atop the Brazilian Shield on the other side of the Amazon Basin. This is because its ancestors inhabited a vast South American plateau which has now been mostly eroded. In the remaining Guianan and Brazilian shields, this lineage of mice has survived.
There are only two “large" animals which are definitively known to live on top of tepuis: the brown-nosed coati and the southern tamandua, a species of anteater. We have photographic evidence in both cases.
There are, however, reports of giant anteaters, pale-throated sloths and even jaguars from the summits. None of these animals have been observed here in modern times, though, and the last claim is especially dubious.
Now for the herpetofauna; the reptiles and amphibians. There are many endemic species, including an incredible diversity of frogs, of which 90 percent are endemic, but not too many which really stand out.
I will however mention a few, such as the lizard Pantepuisaurus rodriguesi. It's not just an endemic species, but a whole unique genus, found only on tepuis.
Its close relative, Riolama inopinata, is also endemic, and has a striking red colouration.
There's also the Neblina anole, a fairly large lizard which can extend a brightly coloured dewlap from its throat:
The Roraima bush toad, a creature that — when threatened — curls up and rolls away:
And the tepui treefrog, which carries its young on its back.
The last component of the tepui wildlife left to review is the invertebrate fauna. There are countless endemic beetles, snails, butterflies, and even aquatic insects and crustaceans in underground rivers.
The only endemic arthropod species which I find particularly noteworthy are an assortment of freshwater crabs recently discovered in the mountains' forests.
So, that's basically everything you need to know about these extraordinary evolutionary laboratories. There is doubtless much left to discover here; many tepuis have long been near-impossible to access even by helicopter, but they're beginning to reveal their secrets.