Picture a fog-wrapped tabletop mountain rising from the jungle on the border of Guyana and Brazil.
A researcher scrambles up in the dark, torch cutting through the mist, and freezes.
Clinging to a leaf is a small brown frog, barely three inches long at most, carrying nine tiny passengers on her back.
That image would turn out to hold a secret far bigger than a new species, one that invites us to look again at something most of us barely notice: a frog’s skin.
A mountain almost nobody climbs
The summit of Wei-Assipu-tepui is accessible only by a technical climb or helicopter.
The otherworldly plateau is about three square kilometers wide, with large crevices fractured into the ground more than 100 meters deep.
The hemiphractid frog genus Stefania is one of many ancient endemic lineages inhabiting the biodiverse Pantepui biogeographical region in the Guiana Shield Highlands of northern South America, the famous “Lost World” of Arthur Conan Doyle.
During his time on the mountain, the researcher noticed numerous cryptic frogs that only came out at night, spotted on the ground, on plant leaves, under rocks, in crevices and on small trees.
Every one of them seemed entirely unremarkable to the untrained eye.
A creature hiding in plain sight
Previous molecular analyses of the Stefania genus had shown that species boundaries are often incongruent with physical appearance, meaning a substantial number of cryptic species remain to be described.
Stefania maccullochi frogs range in size from about 1.8 inches to about 2.9 inches, with females being larger than males.
Their coloring varies greatly, from plain medium brown to chestnut brown and brownish red.
Some animals carry dark markings while others had little to none.
In other words, they are built to look like nothing special.
But the females were doing something that stopped researchers cold.
Nine babies and an ancient contract
This particular frog carries its eggs on her back, and once hatched, the froglets remain there for a period of time.
This backpack method is a form of parental care, helping to ensure the offspring survive at least through the hatching stage.
Most amphibians are not exactly doting parents, simply finding a partner and releasing as many eggs as possible in hopes that some survive.
But in the tropics, different species exhibit remarkable parental care, carrying eggs on the back or brooding them under the skin.
Some tropical frog mothers even feed tadpoles with unfertilized eggs.
So the back is already an extraordinary nursery.
What makes it even more extraordinary has nothing to do with the babies at all.
The hidden truth inside a frog’s skin
The frog’s back is not just a platform for carrying young.
Frogs can absorb oxygen directly through their skin, a process called cutaneous respiration, because their skin is thin, moist and rich in blood vessels.
A network of small blood vessels right underneath the skin absorbs oxygen from water or air, and drives carbon dioxide out in return.
That skin, in other words, is a lung, stretched over the entire body, wrapped around the very back the babies ride on.
“Almost without trying, just having skin that’s moist, and having some blood vessels in it, they’re going to exchange gas and water through their skin, whether they like it or not,” as evolutionary biologist Kurt Schwenk of the University of Connecticut described it.
The mother frog on that summit breathes through the same surface that cradles her nine young: a living cradle and a living lung at once.
Why this wonder matters far beyond one mountain
The new species is likely critically endangered because of its limited range, threatened by climate change, human fires and increasing visitors to its isolated habitat.
Frogs are among the most sensitive indicators of ecosystem health anywhere on Earth, and their skin breathing makes them especially exposed to anything that shifts the chemistry of water or air around them.
Colder water holds higher dissolved oxygen, so warming due to climate change can have significant impacts on populations that breathe through their skin.
When you follow the largest organism on Earth as it fights to survive, or track a new frog species on a forgotten mountain, you are reading the same story: living systems under pressure from a warming world.
The living soil beneath a lawn and the breathing skin of a tiny frog carry the same message: the surface of things holds more life than we ever gave it credit for.
The original study describing Stefania maccullochi, published in the journal Zoological Letters, stands as a reminder that entire worlds of biology still hide on mountains almost no one has visited.
But for the female on that misty summit, carrying nine lives on a surface that breathes, the wonder needs no qualification at all.