They headed toward the noise, but as they got closer and closer, the sound stopped.
The song belonged to a “miniaturized” animal hidden under the leaves , according to a study published Oct. 25 in the peer-reviewed journal PeerJ.
Researchers collected a dozen of the creatures during field surveys between June 2021 and May 2022 and took a closer look at the unfamiliar amphibians. With a gaping mouth and body smaller than a fingernail, the “toadlet” has now been identified as a new species.
Brachycephalus dacnis, or the Dacnis miniature flea-toad, is just 0.3 inches long, according to the study, and is “one of the smallest vertebrates known,” in addition to being part of the second smallest amphibian genus.
“These tiny toadlets are difficult to detect in the field because, apart from the brightly colored species, the smallest species are generally cryptic by matching the background coloration pattern,” researchers said.
The toadlet has fewer fingers and toes than “typical frog(s)” and a “yellowish-brown” body, according to the study.
Some have a darker brown stripe that runs from the tip of their snout down to their back legs. Mottled back colors varied from toadlet to toadlet, researchers said.
“Some frogs have a leaf-like (back) coloration, while others have a rock-like (back) coloration,” researchers said.
The miniature flea-toad also has black pupils with a bronze iris, according to the study.
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“The new species is vocally active throughout the year, with peaks of activity when the humidity was higher than 90% (more than) 50 males calling,” researchers said. “The calling activity was mostly detected during daytime … or anytime of the day after heavy rains. From August to April, we also heard calls during the night.”
The calls — one or two sets of multiple pulses — would stop for several minutes when the new species sensed researchers nearby but would then pick up again, researchers said. Other frogs “exhibited mouth-gaping” when researchers neared.
The toadlets were primarily found in the leaf litter at the bottoms of slopes in a forest valley, according to the study. They also appeared in an area of shorter shrubs under a thick layer of litter.
This is now the seventh identified flea-toad species, but researchers believe there may be ”many more” that remained undiscovered because of their hidden habitats, extremely small size and camouflaged coloration, according to the study.
The new species was found in the Projeto Dacnis private reserve, from where it gets its name. The reserve is in Ubatuba, São Paulo, Brazil, along the southeastern coast of the Atlantic Ocean.
The research team includes Luís Felipe Toledo, Lucas Machado Botelho, Andres Santiago Carrasco-Medina, Jaimi A. Gray, Julia R. Ernetti, Joana Moura Gama, Mariana Lucio Lyra, David C. Blackburn, Ivan Nunes and Edelcio Muscat.