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Tiny frog the size of a PEA is the world’s smallest vertebrate


Scientists have discovered a frog the size of a pea hiding in a Brazilian forest that could be the world’s smallest vertebrate.

The ‘flea toad’ measures just 7.1 millimeters, on average, making it now the world’s tiniest — after researchers successfully measured 46 total specimens of the miniscule amphibian found across its hilltop forest habitat in southern Bahia, Brazil.

The little frog’s top-facing back blends into its surroundings in a ‘ground color’ of varying browns, unlike many of the vivid yellow or orange frogs in similar locales.

Male flea toads proved to be competitively the the species’ smallest half, with their female counterparts measuring an average of 8.15 mm, or just slightly larger than the previous record-holder: the Paedophryne amauensis frog of Papua New Guinea.

While biologists have been aware of the flea toad's pea-sized existence (above) since it was first identified in 2011, it took a comprehensive survey of 46 specimens to confirm that it was really the world's smallest

While biologists have been aware of the flea toad’s pea-sized existence (above) since it was first identified in 2011, it took a comprehensive survey of 46 specimens to confirm that it was really the world’s smallest

To illustrate just how small Brazil's new record-breaking flea toad really is, the researchers also photographed the little creature on a 1 Brazilian Real coin. The coin has a diameter of 27 mm and a thickness of 1.95 mm. Well over a dozen adult flea toads could fit on a single Real

To illustrate just how small Brazil’s new record-breaking flea toad really is, the researchers also photographed the little creature on a 1 Brazilian Real coin. The coin has a diameter of 27 mm and a thickness of 1.95 mm. Well over a dozen adult flea toads could fit on a single Real

Biologists have been aware of the flea toad’s pea-sized existence since it was first discovered living in Bahia’s Atlantic rainforest in 2011, as first published in Zootaxa.  

But took this new and more comprehensive survey of specimens to prove that the team had obtained enough adult frog samples to draw a firm conclusion on the species’ average size. 

‘Sizes smaller than average should be confirmed as being adult,’ reads the new study, ‘which can be done by direct observation of the gonads.’

Their measurements, the researchers reported in the peer-reviewed journal Zoologica Scripta this January, helped them quickly assess if the toads were adults by determining ‘if they are reproductively mature or not.’ 

The scientists, which included herpetologists affiliated with German and Brazilian universities, also examined the frogs for the presence of vocal slits in their throats: a feature that only the males of the species have.

The results were ‘absolutely clear’ according to Mark Scherz, who studies amphibians and reptiles as the Curator of Herpetology at the Natural History Museum of Denmark in Copenhagen.

‘These really are potentially the smallest extant frogs in the world, which is astonishing,’ Scherz told New Scientist

Above, one of the flea toad's losing competitors, the pumpkin toadlet or Brachycephalus ephippium, also posed with another Brazillian 1 Real coin

Above, one of the flea toad’s losing competitors, the pumpkin toadlet or Brachycephalus ephippium, also posed with another Brazillian 1 Real coin

Above, another of the flea toad's losing competitors, the Izecksohn's Flea Toad Brachycephalus didactylus, posing on a tiny mushroom

Above, another of the flea toad’s losing competitors, the Izecksohn’s Flea Toad Brachycephalus didactylus, posing on a tiny mushroom

Scherz, an independent expert unaffiliated with the authors of the new study, told the publication that he was impressed by just how small the tiniest of the tiny adult flea toads could be. 

‘It’s 6.45 millimeter [in length], which is 30 percent smaller than any adult male frog I have ever seen,’ Scherz said. 

‘It’s almost one millimeter smaller than the next smallest frog.’

The range of adult male flea toad lengths, the researchers found, were between 6.45 mm and 7.90 mm.

For the adult female flea toads, the range was 7.38 mm to 9.87 mm. 

To better illustrate just how small Brazil’s new record-breaking flea toad really is, the researchers also photographed the little creature on a 1 Brazilian Real coin.

The seven-gram coin has a diameter of 27 mm and a thickness of 1.95 mm. 

Well over a dozen adult flea toads, formally known as Brachycephalus pulex, could fit on the face of a single Real coin.

‘Identifying the smallest frog in the world has been no easy challenge,’ the team  confessed in their new report.

For starters, the species only seems to exist on two forested hilltops in the southern Bahia region of Brazil. 

The study’s lead author, herpetologist Dr. Mirco Solé at the State University of Santa Cruz in Brazil, had to get permission to work on the property by the owners of the private Serra Bonita Reserve, Clemira Souza and Vitor Osmar Becker.

They also need to source additional flea toad or B. pulex samples from the Célio Fernando Baptista Haddad Amphibian Collection.

Solé and his co-authors noted that it was remarkable that even for these pea-sized tiny frogs, the males were smaller than the females — a form of ‘sexual dimorphism’ that is true of 90 percent of all frog and toad species, both ‘anuran’ amphibians.

The researchers were also impressed that the smallness of B. pulex meant that it effectively had no hard ‘bony elements’ aside from a very hard and thick, or ‘hyperossified,’ skull and spine. 

But, as Solé and his team suggested in their paper, the flea toad may not hold onto its crown for long, asking: ‘Has the lower limit of vertebrates really been reached?’ 



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