Newly Discovered Mini Frogs Are So Very Very Tiny

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CC BY 4.0. Mini mum on a thumb. (Photo: Andolalao Rakotoarison)

The teeny amphibian inhabitants of Madagascar could fit four on a thumbnail.

What do the words minimum, miniature, and miniscule have in common? Well of course they all share the word-forming element, "mini," suggesting something supremely teeny – but now the three share something else as well. They serve as official science names for three tiny frog species newly discovered in Madagascar.

Meet Mini mum, Mini ature, and Mini scule, who “are astronomically small,” says Mark Scherz, an evolutionary biologist at Ludwig-Maximilians Universität in Munich, Germany. Scherz described these and two other tiny new frog species in a new study published in the journal PLoS ONE.

“You could sit the brain on the top of a pin. It’s amazing that they have all the same organs you or I have in our bodies, but in a package that can fit four times on your own thumbnail,” he told National Geographic.

As part of his PhD, Scherz has been studying frogs and reptiles on Madagascar, a tiny paradise with more than 350 frog species. In an essay published in The Conservation, Scherz notes that the island possibly has the highest frog diversity per square kilometer of any country in the world. "And many of these frogs are very small," he writes.

Just how small are they? Well the newly discovered ones – who in fact have given birth to a new genus – range in size from 8 mm (one-third of an inch) to 15 mm (just over half an inch). The smallest of the three is just a tad bit longer than a gran of rice. Scherz explains:

"We’ve dubbed three of the new species as “Mini” – a group that is wholly new to science. When a whole group or “genus” like this is new to science, it needs a name, so that information about it can be accumulated with a fixed anchor. We also wanted to have a bit of fun. And so, we named the species Mini mum, Mini scule, and Mini ature. Adults of the two smallest species – Mini mum and Mini scule – are 8–11 mm, and even the largest member of the genus, Mini ature, at 15 mm, could sit on your thumbnail with room to spare."

Miniature frogs have been difficult to study because once frogs get so small, they look very similar – making it hard to know how diverse they really are, Scherz explains. Interestingly, the newly identified frogs belong to three different groups that are not closely related to one another – yet they have all independently evolved into their perfect tiny selves. Scherz says that the evolution of body size in Madagascar’s miniature frogs has been more dynamic than previously understood.

"What’s remarkable is that the smallest frogs have evolved to become tiny again and again, often several times within a single region, as highlighted in this new study, he writes. "This means there must be some kind of advantage to being a tiny frog or something that allows tiny frogs to survive, thrive, and diversify."

These are the new frogs:

Mini mum: Found in Manombo in eastern Madagascar. It is one of the smallest frogs in the world, reaching an adult body size of 9.7 mm in males and 11.3 mm in females. It could sit on a thumbtack.

Mini scule: From Sainte Luce in southeastern Madagascar is slightly larger and has teeth in its upper jaw.

Mini ature: Found in Andohahela in southeast Madagascar – a bit larger than its relatives but is similar in build.

Rhombophryne proportionalis: Found in Tsaratanana in northern Madagascar, Scherz says this one is unique among Madagascar’s miniaturised frogs because it’s a proportional dwarf, "meaning it has the proportions of a large frog, but is only about 12 mm long. This is very unusual among tiny frogs, which usually have large eyes, big heads, and other characters that are 'baby-like'.".

Anodonthyla eximia: Found in Ranomafana in eastern Madagascar, this one is distinctly smaller than any other Anodonthyla species. "It lives on the ground, providing evidence that miniaturisation and terrestriality may have an evolutionary link," writes Scherz. "Maybe getting really small makes it hard to stay up in the trees."

Noting that Madagascar is a treasure trove of biodiversity, Scherz says that it is one of the best places in the world to study reptiles and amphibians and their evolutionary processes. Alas, a familiar theme presents itself.

"We are aware that we’re working in a very tight time frame," he writes. "Madagascar’s forests are dwindling at an astounding rate .... Conservation work in the country is intensifying, but there is still a long way to go before we can consider species like Mini mum and Mini scule safe for the foreseeable future."