Tiny steps towards greater knowledge: An osteological review with novel data on the Atlantic Forest toadlets of the Brachycephalus ephippium species group

Abstract

Brachycephalus is a small, endemic genus of anurans that occur throughout the Brazilian Atlantic Forest. Recent analyses corroborated the monophyly of two species groups within this genus (B. ephippium and B. pernix), whereas the B. didactylus group appears to be polyphyletic. Herein, we compare and describe the skeletal system of all species from the Brachycephalus ephippium species group. We investigated diagnostic characters that are potentially useful to delimit similar species, confirmed the previously proposed genus definition and added six extra characters. We propose an osteological diagnosis for each species of the B. ephippium group, evaluating and describing intraspecific variations. Our results suggest that adults of B. ephippium group have ornamented parotic plates, ornamented post‐orbital crests, absence of quadratojugal and neopalatines, distal end of the otic ramus of squamosal expanded towards the parotic plate, reduced zygomatic ramus of the squamosals, posterolateral projection of the crista parotica, presence of ornamented spinal plates (except B. alipioi) and ornamented paravertebral plates. We highlighted the importance of including more than one specimen per species when dealing with miniaturized taxa. A comparison with other Brachycephalus species groups and with Ischnocnema was also provided. Lastly, we suggest some characters to be included in future phylogenetic analysis.

Initial Phylotranscriptomic Confirmation of Homoplastic Evolution of the Conspicuous Coloration and Bufoniform Morphology of Pumpkin-Toadlets in the Genus Brachycephalus

“…In the B. ephippium group, species have remarkably ossified skulls and vertebral columns, sometimes with a bony dorsal shield, and bone sculpturing consisting of ridges and crests inducing a reticulated or pitted pattern in the skull, spinal processes of sacral, and presacral vertebrae [20,25]. In contrast, in the B. pernix group, such hyper-ossification is not observed [19,20,27]. This might indicate that the bufoniform appearance of these toadlets is ontogenetically based on different developmental processes, which would be in agreement with an independent evolutionary origin.…”

“…Surprisingly, early molecular phylogenetic evidence (Figure 2A) suggested that these two morphological groups are not reciprocally monophyletic within Brachycephalus [18]. Based on DNA sequences of few mitochondrial and two nuclear-encoded genes (tyrosinase and recombination activating gene 1), two major clades of pumpkin-toadlets were recovered: the B. ephippium group (with 15 species), characterized by a gradient of increased mineralization in the skull [20,[24][25][26][27], and the B. pernix group (with 19 species), which is not hyperossified [18][19][20]. The B. ephippium group is distributed across the Serra do Mar and Serra da Mantiqueira mountain ranges whereas the B. pernix group is distributed across the Serra do Mar, respectively at the north and south of the Guapiara Lineament [19] (Figure 1).…”