Six new species of tiny frog that live in forests of Mexico discovered by University of Cambridge researchers
Six previously unknown species of frog - each the size of a thumbnail - that live in the forests of Mexico have been discovered.
The adult male of one of the species - Craugastor candelariensis, grows to a mere 13mm, making it Mexico’s smallest known frog. And all of them are smaller than a one pence coin - growing to less than 18mm long.
They are known as ‘direct-developing’ frogs because rather than hatching from eggs into tadpoles like most frogs, they emerge from the eggs as perfect miniature frogs.
Being so tiny, they are at the bottom of the forest food chain.
Tom Jameson, a researcher at the University of Cambridge’s Department of Zoology and University Museum of Zoology, who led a study into them, said: “With millions of these frogs living in the leaf litter, we think they’re likely to play a hugely important role in the ecosystem as a source of food for everything else, from lizards to predatory birds.
“Until now, these new species have gone unnoticed because they’re small and brown and look really similar to other frogs.
“Their lifestyle is utterly fascinating. These frogs live in the dark, humid leaf litter of the forests, which is like a secret world - we don’t really know anything about what goes on there. We don’t understand their behaviour, how they socialise, or how they breed.”
The discovery was made by researchers at the University of Cambridge, London’s Natural History Museum and the University of Texas at Arlington and their findings have been published in the journal Herpetological Monographs.
The researchers gathered almost 500 frog specimens from museums around the world, which had been collected in Mexico and used new methods to categorise relationships between them.
They then used DNA sequencing to sort the frogs into groups based on how similar their genes were.
CT scans were used to create 3D models of the frogs’ skeletons, in order to compare physical details.
The two different approaches revealed six new species of frog.
Tom said: “Frogs in the group known as Craugastor are very difficult to tell apart, so scientists have long suspected that more species may exist. We’re really excited to have discovered six new Craugastor species that are completely new to science.”
They have been named Craugastor bitonium, Craugastor candelariensis, Craugastor cueyatl, Craugastor polaclavus, Craugastor portilloensis, and Craugastor rubinus.
Tom is pleased by the name cueyatl as it means ‘frog’ in the indigenous language, Nahuatl, which is spoken in the Valley of Mexico where this species was found.
“We chose the name cueyatl to honour the rich human history of the Valley of Mexico, and the local people who have probably known these frogs far longer than we have,” he said.
But the frogs are incredibly vulnerable.
They are known as ‘micro-endemics’, as some may occur only in just one small area, such as a hilltop in a specific part of Mexico.
“We named Craugastor rubinus after the garnet mines in the hillside where they’re found,” said Tom. “Sadly, it will only take the expansion of one mine and these frogs could be gone.”
Climate change leading to habitat loss is another threat, along with the deadly fungal disease chytridiomycosis, which is decimating amphibian populations across the world.
But the researchers have identified key protected areas throughout Mexico where the six new species live and they hope to work with the government and NGOs in Mexico to connect these areas together.
Tom said: “These frogs potentially play a really important role in the forest ecosystem. We need to make sure that they don’t just get wiped off the map because no-one even knows they’re there.”
And there are probably many more species of Craugastor frog yet to be discovered.
“We’ve looked at the maps of where the original expeditions went looking for frogs in Mexico, and found whole valleys and river systems where nobody went,” said Tom.
“Because the tiny frogs live in tiny areas we can be pretty confident there’s a whole bunch of other undiscovered species there – all we have to do is go and find them.”
Some specimens of Craugastor portilloensis were even smaller than 13mm, but the researchers could not be sure that they were fully grown adults.
As tiny as they are, none of them can lay claim to the title of the world's smallest frog. That belongs to adult males of the species Paedophryne amanuensis, a frog from Papua New Guinea which does not even reach 8mm.