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| Brachycephalus dacnis Toledo, Botelho, Carrasco-Medina, Gray, Ernetti, Gama, Lyra, Blackburn, Nunes & Muscat, 2024 |
Abstract
The genus Brachycephalus includes miniaturized toadlets with two distinct morphotypes: brightly colored species with a bufoniform phenotype and smaller, cryptic species with a leptodactyliform phenotype. The diversity of leptodactyliform species is still underappreciated, and we generally lack fundamental information about their biology. Recent sampling efforts, including DNA analyses and recordings of advertisement calls, have improved our understanding of this group. In the present study, we describe a new species of Brachycephalus, one of the smallest vertebrates known. This new species is distinguished from its congeners by a combination of morphological, bioacoustic, and genetic data. Despite being among the smallest frogs globally (the second smallest amphibian species), it exhibits skeletal traits typical of larger frogs, such as the presence of cranial bones that are lost or fused in other miniature frogs, including other Brachycephalus. Our description underscores how new discoveries within the megadiverse fauna of the Atlantic Forest—a rich biodiversity hotspot—can provide insights into phenotypic variation, including vertebrate body size. By describing this new species, we also aim to revisit the hypothesis that the type series of B. hermogenesi includes two species, potentially including individuals of the species described here.
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| Brachycephalus dacnis paratype (ZUEC-AMP 25612) adult male, SVL = 7.89 mm. (A) Dorsal view, (B) ventral view, (C) ventral view of hand, (D) ventral view of feet. |
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| Brachycephalus dacnis paratype individuals found at the Projeto Dacnis private reserve, municipality of Ubatuba, state of São Paulo, Brazil. (A) ZUEC-AMP 25272; (B) ZUEC-AMP 25274; (C and D) ZUEC-AMP 25275 displaying mouth-gaping behavior and the same individual on top of one herpetologist’s fingertip. |
Brachycephalus dacnis sp. nov.
Diagnosis–The new species is assigned to the genus Brachycephalus because of its miniature body size, fewer phalanges and toes than a typical frog, fingers and toe tips not expanded but apically pointed, and toes lacking circumferential grooves. The new species can be diagnosed from its congeners by the following combination of characters: (1) “leptodactyliform” body shape; (2) adult body length (SVL) smaller than 1 cm; (3) distinct and functional toes II and V; (4) presence of vestigial fingers I and IV; (5) distinct iris; (6) absence of dark markings on the skin over the pectoral region; (7) dark black or pale brown marbled venter with small white blotches in preserved specimens; (8) and advertisement call composed of one or two multi-pulsed (3–7 pulses) note with dominant frequency between 8.01 and 8.44 kHz, note duration between 0.03–0.08 s (when isolated), up to 0.41 s (when in pairs), and absence of attenuated notes.
Etymology–The specific epithet name ‘dacnis’ honors the Projeto Dacnis private reserve and NGO that has supported biodiversity research since 2010 in the municipalities of São José dos Campos, Miracatu and Ubatuba (where the new species was discovered), state of São Paulo, Brazil. The name is used as an invariable noun in apposition to the generic name.
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 amd Edelcio Muscat. 2024. Among the World’s Smallest Vertebrates: A New miniaturized Flea-toad (Brachycephalidae) from the Atlantic rainforest. PeerJ. 12:e18265 DOI: doi.org/10.7717/peerj.18265
