Just over seven millimeters in length, it was discovered in 2011 in the Brazilian jungles, and could be the smallest vertebrate ever to exist in nature. We are talking about Brachycephalus pulex, a microscopic frog described in a recent study by the State University of Santa Crux which studied its size, anatomy, and the incredible adaptations it had to undergo to reach such small dimensions. And according to the authors of the research, published in the journal Zoologica Scripta, the evolutionary sacrifices that the Brazilian flea frog (this is its common name) had to face probably make it impossible for any vertebrate to go further: smaller than that, in short, no you can become, at least if you also want to continue to have a bony skeleton.
“Our data shows that the flea frog is officially the smallest frog and the smallest vertebrate species in existence,” underlines Wendy Bolaños, a herpertologist at the State University of Santa Cruz who collaborated on the research. “I can assure you that identifying the smallest frog in the world was no walk in the park.”
In fact, Brachycephalus pulex was first described in 2011, but dozens of patient measurements were needed to confirm the average size of the species. In the end, after studying 46 specimens of both sexes, and carefully analyzing their gonads to confirm that they were adults, the researchers determined an average length of 7.1 millimeters for males, and 8.15 for the females, which in frogs are always the largest sex.
Confirmation of the flea frog record also required the careful study of dozens of specimens of the direct contender, the Paedophryne amauensis frog native to Papua New Guinea, which at the end of the analyzes stopped at an average length of 7.7 millimeters (per males). In short, for 0.6 millimetres, the title goes to the Brazilian fleas. And it is a deserved recognition, given what they had to sacrifice to reach such microscopic dimensions: they only have three toes on each paw (one of which is vestigial), they cannot jump, they are deaf, and they have replaced all the bones of the body with cartilage, a part of the spine and the skull.
Evidently, the advantages obtained in terms of physical safety (such small dimensions make them difficult prey to identify) and nutritional safety (they need very small quantities of food to survive) have proven to be greater than the disadvantages imposed by the extra small size. Certainly, this is a difficult record to beat: a 2022 study, in fact, calculated that under 6 millimeters in length it becomes almost impossible for a vertebrate to make room for all the cells required by its organs, and for a quantity of enough eggs to support a stable population. And since we are just a millimeter away from this minimum limit, it is likely that Brazilian flea frogs are the smallest vertebrate that can exist on our planet.