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A frog smaller than a pencil eraser has hopped into the record books as the one of the smallest vertebrates known to science. Researchers formally described the species in late October 2024 after encountering it in the Atlantic Forest in southeastern Brazil's São Paulo state.
At a length of 6.95 millimeters (0.27 inches), Brachycephalus dacnis has given scientists a new appreciation of just how small vertebrates can get. The only known frog smaller than this, found in February 2024 in northeastern Brazil, beats it by just 0.5 mm (0.02 in) but struggles with balance.
Frogs in the tiny Brachycephalus genus are notorious for their clumsy landings, often tumbling over or falling on their heads after jumping, as their vestibular systems were compromised in their evolution to be small.
But the B. dacnis retained its inner ear structure, allowing it to hear and leap quite proficiently. Researchers found that it can jump an impressive 32 times its own size, with surprising grace.
"The size makes this frog very special," Edelcio Muscat, one of the researchers who described B. dacnis and a coordinator at Projeto Dacnis, a conservation NGO working in the Atlantic Forest, told Mongabay by phone. "The miniaturization process hasn't affected any of its organs or its skeleton."
In 2016, Muscat was on a typical nighttime expedition carefully turning over leaves on the forest floor when one of the frogs jumped out. Recordings of its croak, more akin to a cricket's chirp than a typical toad's ribbit, would confirm it was a unique species years later.
Brazil is home to the world's largest number of amphibian species, most of them in the Atlantic Forest, a biodiversity hotspot encompassing Brazil's largest cities, São Paulo and Rio de Janeiro, with dozens of species described every year. Just 13% of the original Atlantic Forest remains.
"The discovery of this species reveals how much we've lost without even realizing it," Adrian Garda, a herpetologist at the Federal University of Rio Grande do Norte, not involved in the study, told Mongabay by phone. "Right before our eyes, such a peculiar and extremely miniaturized vertebrate existed. What might we have lost over the past 40 to 80 years of industrialization?"
Worldwide, nearly 41% of amphibian species are threatened with extinction, compared with 26.5% of mammals, 21.4% of reptiles and 12.9% of birds.
B. dacnis is speckled brown and white and has survived by blending in and laying low. Its tiny size helps it avoid predators, and the leaves of the forest floor provide thermal comfort, which might help protect it against the brunt of climate change, Muscat said.
"The discovery shows us how much we need to preserve the Atlantic Forest," Muscat said. "There are still species it supports that we have not yet found."