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Brazilian flea toad may be the world鈥檚 smallest vertebrate

Male Brachycephalus pulex frogs are so small that two of them can sit side by side on a pinky nail

By Jake Buehler

13 February 2024

A flea toad perches on 1 Brazilian real (the coin has a diameter of 27 millimetres)

Renato Gaiga

A tiny Brazilian frog about the size of a pea may threaten the current record-holder for the world鈥檚 smallest vertebrate.

The flea toad Brachycephalus pulex, which is actually a frog species, was first described by scientists in 2011. Shortly after, at the State University of Santa Cruz in Brazil wondered if the species could be the smallest amphibian yet discovered. But only a handful of specimens had been collected from the frogs鈥 only known habitat on two forested hilltops in southern Bahia, Brazil. And their gonads hadn鈥檛 been examined, which is necessary to confirm if they are adults.

Sol茅 and his colleagues measured the body lengths of 46 flea toads, verifying the frogs鈥 maturity and sex by examining their gonads and checking for the presence of vocal slits in their throats, something only males have.

Adult B. pulex males average a touch over 7 millimetres long, slightly smaller than the females. This makes them smaller than the males of Paedophryne amauensis, a frog from Papua New Guinea that was, until now, considered both the smallest amphibian and smallest vertebrate.

鈥淚t鈥檚 absolutely clear,鈥 says at the Natural History Museum of Denmark in Copenhagen. 鈥淭hese really are potentially the smallest extant frogs in the world, which is astonishing.鈥

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It isn鈥檛 just the average size that is shocking, but how small these flea toads can get compared with other mini frogs 鈥 illustrated by the smallest specimen in the study. 鈥淚t鈥檚 6.45 millimetres [long], which is 30 per cent smaller than any adult male frog I have ever seen,鈥 says Scherz. 鈥淚t鈥檚 almost one millimetre smaller than the next smallest frog.鈥

At such small scales, frogs develop strange anatomical quirks, such as losing toes or having such underdeveloped ears that . Some species can hardly jump because their balance organs are so wee.

Yet there might even be smaller vertebrates still undiscovered, says Sol茅.

Journal reference

Zoologica Scripta

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