The oral apparatus of anuran tadpoles is a unique structure composed of soft and keratinized parts surrounding the mouth. Among the many variations, a common oral apparatus involves a dorsal gap in the marginal papillae, keratinized jaw sheaths, and two upper and three lower rows of labial teeth. In Leiuperidae, besides this generalized morphology, four configurations are distinguished by the arrangement of the lower marginal papillae and the number of lower tooth rows. Study of the early oral ontogeny in 12 species representing these five configurations shows variations in the development of the lower marginal papillae and the third lower labial tooth row. Similar configurations may result from similar pathways (e.g. Physalaemus cuvieri group and Pseudopaludicola falcipes) or different pathways (e.g. generalized oral discs of Pleurodema and Physalaemus). Different oral configurations may result from overlapping trajectories ending at different stages (e.g. Physalaemus riograndensis and Ph. biligonigerus) or different trajectories (e.g. Ph. henselii and Ph. gracilis). Further studies are needed to interpret the role that heterochrony has played in evolutionary change within this family. The unsuspected variation occurring in this transient structure highlights its evolutionary potential and might be insightful in studies of anuran phylogenies that are largely based on adult characters.

We studied the oral apparatus, buccal cavity and musculoskeletal features in tadpoles of five species of the genus Scinax (S. acuminatus, S. uruguayus, S. aff. pinima, S. aromothyella, and S. berthae). Observed variation is mainly related to intrageneric grouping. Scinax acuminatus (S. ruber clade, sister taxon of S. rostratus group) has a distinctive combination of a mental gap in the margin of oral papillae, straight labial teeth with few or absent cusps, processus muscularis acute and posteriorly directed, and m. subarcualis rectus I with two slips. Scinax uruguayus and S. aff. pinima (S. uruguayus group) have keratinized sheets ventrolateral to the lower jaw sheath, well-developed infralabial and lateral ridge papillae, robust jaw cartilages, cornua trabeculae with short and widely divergent free portions, processus articularis short and wide, processus muscularis thin and directed anteriorly. Scinax aromothyella and S. berthae (S. catharinae group) have poorly developed, non-colored spurs behind the lower jaw sheath, long and thin processus articularis, wide and rounded processus muscularis, and tripartite cartilago suprarostralis. Anatomical features described are congruent with current phylogenetic arrangements based on molecular, chromosomal, and morphological data, and provide a source of information that can be useful to solve interspecific relationships within Scinax.

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The study of early development in Neotropical Leiuperinae frogs (Anura, Leptodactylidae) has been addressed by several works in recent times. However, a comparative developmental approach under a phylogenetic context was not available. Herein we analyzed the morphological and ontogenetic diversity of embryos belonging to 22 species of the three largest genera in Leiuperinae. We find that in most cases, variations fit with the phylogeny at the inter- and intrageneric levels. Embryo kyphosis and whitish color are synapomorphies for the clade grouping Physalaemus and Engystomops . The presence of a third lower tooth row on the oral disc is plesiomorphic for Leiuperinae, only changing in derived clades. The configurations and developmental trajectories of the lower lip are exceptionally diverse. The developmental sequences optimized on the phylogenetic tree recover an early differentiated first lower tooth row a synapomorphy of Pseudopaludicola and Physalaemus , and an early differentiated second row as synapomorphy of Pleurodema . On the other hand, few features are highly conserved in the subfamily, such as the adhesive glands universally present in a type-C configuration. Our results also suggest that the morphology and ontogeny of embryos is in some cases associated to the environment where they develop. A large body size, poorly developed transient respiratory structures, large yolk provision and delayed development of the digestive tract occur convergently in embryos inhabiting cold, oxygenated environments. Embryos that develop in warmer water bodies in xeric environments show more complex and persistent transient respiratory structures and an early onset of hind limbs development. Our survey highlights that morphology and early development of anurans can be a valuable source of information for phylogenetic studies, and provide fundamental bases to explore and discuss how evolutionary changes can be shaped by environmental conditions.

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We present a comprehensive review of larval morphology in the Neotropical toad genus Melanophryniscus. The taxa studied included 23 species with representatives of recognized phenetic groups and different larval ecomorphological guilds: pond, stream, and phytotelm-dwelling tadpoles. Their external morphology variation is congruent with current phenetic arrangement based on adult features, but also reflects the habitat where larvae develop. Lotic tadpoles (i.e. M. tumifrons group and M. krauczuki) in general exhibit a more depressed body, a longer tail with lower fins, and larger oral discs than lentic forms (i.e. M. stelzneri group, M. moreirae, *Corresponding author. E-mail: diegobaldo@gmail.com M. sanmartini, and M. langonei).Despite their peculiar, confined microhabitat, phytotelm larvae do not diverge markedly from non-arboreal species. The distinctive features of all species are the presence of a pineal end organ and the placement of the intestinal reversal point at the left of the abdomen in typical larval stages. The buccal cavity and musculoskeletal anatomy are quite conserved between species, yet some characteristics differ from those of other bufonids. The presence of one pair of subhyoid muscles is apparently an exclusive trait of Melanophryniscus among Bufonidae.

Within Anura, direct development involves ontogenetic changes of the biphasic ancestral pattern. The recent partitioning of the genusEleutherodactylus, along with the proposition of the unranked taxon Terrarana, has renewed an interest to the morphological and ecological diversity among direct-developing frogs. The morphological changes during embryonic development ofOreobates barituensisis similar to those of other Neotropical direct-developing species, including the reduction or absence of several larval and embryonic characters (e.g., external gills and adhesive glands), heterochronic changes (e.g., early developing limbs and late persistence of ciliated epidermal cells), and the appearance of new structures (e.g., egg tooth). The tail achieves an extraordinary peramorphic development (encloses the entire embryo), and the location of its expanded part is interpreted as a heterotopic change resulting in a novel trait. An enveloping tail with apparently non-heterotopic fins, combined with the absence of gills, has been only reported for a species of the related genusCraugastor, and these morphologies suggest an informative perspective for the study of evolution of direct development in terraranans.