All six species are smaller than a British 1p coin — around 15mm long — when fully grown. Adult males of the tiniest of these species, named Craugastor candelariensis, grow to only 13mm.
The newly discovered species are known as ‘direct-developing’ frogs: rather than hatching from eggs into tadpoles like most frogs, they emerge from the eggs as perfect miniature frogs. And they’re so small that they’re right at the bottom of the forest food chain.
“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,” said Jameson.
The discovery, by researchers at the University of Cambridge, London’s Natural History Museum, and the University of Texas at Arlington, is published in the journal Herpetological Monographs.
“Until now these new species have gone unnoticed because they’re small and brown and look really similar to other frogs,” said Tom Jameson, a researcher at the University of Cambridge’s Department of Zoology and University Museum of Zoology, who led the study.
The study involved gathering almost 500 frog specimens from museums around the world, which had been collected in Mexico, and using new methods to categorise the relationships between them.
Using DNA sequencing, the team sorted the frogs into groups based on how similar their genes were. Then CT-scanning was used to create 3D models of the frogs’ skeletons, so that physical details could be compared. These two very different lines of evidence revealed six new species of frog.
The new species have been named Craugastor bitonium, Craugastor candelariensis, Craugastor cueyatl, Craugastor polaclavus, Craugastor portilloensis, and Craugastor rubinus. Jameson is particularly pleased with the name cueyatl — it means ‘frog’ in the indigenous language, Nahuatl, spoken in the Valley of Mexico where this species was found.
Known as ‘micro-endemics’, some of the newly discovered frogs may occur only in one small area, such as a hilltop in a certain part of Mexico. This makes them incredibly vulnerable.
Habitat loss can also result from climate change. And the frogs are threatened by a deadly fungal disease, chytridiomycosis, that’s wiping out amphibian populations across the world.
But the researchers are hopeful that there’s a future for their tiny frogs. They have identified key protected areas throughout Mexico where the six new species live — and now hope to work with the government and NGOs in Mexico to connect these areas together.
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