Despite the wide variety of adaptive modifications in the oral and facial regions of vertebrates, their early oropharyngeal development is considered strictly uniform. It involves sequential formation of the mouth and pharyngeal pouches, with ectoderm outlining the outer surface and endoderm the inner surface, as a rule. At the extreme anterior domain of vertebrate embryos, the ectoderm and endoderm directly juxtapose and initial development of this earliest ecto-endoderm interface, the primary mouth, typically involves ectodermal stomodeal invagination that limits the anterior expansion of the foregut endoderm. Here we present evidence that in embryos of extant non-teleost fishes, oral (stomodeal) formation is preceded by the development of prominent pre-oral gut diverticula (POGD) between the forebrain and roof of the forming mouth. Micro-computed tomography (micro-CT) imaging of bichir, sturgeon and gar embryos revealed that foregut outpocketing at the pre-oral domain begins even before the sequential formation of pharyngeal pouches. The presence of foregut-derived cells in the front of the mouth was further confirmed by in vivo experiments that allowed specific tracing of the early endodermal lining. We show that POGD in sturgeons contribute to the orofacial surface of their larvae, comprising oral teeth, lips, and sensory barbels. To our knowledge, this is the first thorough evidence for endodermal origin of external craniofacial structures in any vertebrate. In bichir and gar embryos, POGD form prominent cranial adhesive organs that are characteristic of the ancient bauplan of free-living chordate larvae. POGD hence seem arguably to be ancestral for all ray-finned fishes, and their topology, pharyngeal-like morphogenesis and gene expression suggest that they are evolutionarily related to the foregut-derived diverticula of early chordate and hemichordate embryos. The formation of POGD might thus represent an ancestral developmental module with deep deuterostome origins.

Cercosaurine lizards (subfamily Cercosaurinae of the family Gymnophthalmidae) represent a substantial component of the reptile fauna in the Neotropics. Several attempts have been made to reconstruct the phylogenetic relationships within this group, but most studies focused on particular genera or regions and did not cover the subfamily as a whole. In this study, material from the montane forests of Peru was newly sequenced. In combination with all cercosaurine sequences available on GenBank, an updated phylogeny of Cercosaurinae is provided. Monophyly was not supported for three of the currently recognised genera (Echinosaura, Oreosaurus, and Proctoporus). The genus Proctoporus is formed by five monophyletic groups, which should be used in future taxonomic revisions as feasible entities. Recognition of two previously identified undescribed clades (Unnamed clades 2 and 3) was supported and yet another undescribed clade (termed here Unnamed clade 4), which deserves recognition as an independent genus, was identified herein. Selvasaura brava, a new genus and new species of arboreal gymnophthalmid lizard is described from the montane forests of the Pui Pui Protected Forest, Provincia de Chanchamayo, Región Junín, Peru. The new species is characterised by its small size (SVL 42.1–45.9 mm), slender body, smooth head shields, presence of paired prefrontal shields, fused anteriormost supraocular and anteriormost superciliary shields, transparent not divided lower palpebral disc, slightly rugose subimbricate rectangular dorsal scales in adults (slightly keeled in juveniles), distinctly smaller but non-granular lateral scales, smooth squared to rectangular ventral scales, and hemipenial lobes large, distinct from the hemipenial body. Phylogenetic affinities of the new genus to the other cercosaurine genera, as well as basal phylogenetic relationships between the other cercosaurine genera remain unresolved.

In most vertebrates, pharyngeal arches form in a stereotypic anterior-to-posterior progression. To gain insight into the mechanisms underlying evolutionary changes in pharyngeal arch development, here we investigate embryos and larvae of bichirs. Bichirs represent the earliest diverged living group of ray-finned fishes, and possess intriguing traits otherwise typical for lobe-finned fishes such as ventral paired lungs and larval external gills. In bichir embryos, we find that the anteroposterior way of formation of cranial segments is modified by the unique acceleration of the entire hyoid arch segment, with earlier and orchestrated development of the endodermal, mesodermal, and neural crest tissues. This major heterochronic shift in the anteroposterior developmental sequence enables early appearance of the external gills that represent key breathing organs of bichir free-living embryos and early larvae. Bichirs thus stay as unique models for understanding developmental mechanisms facilitating increased breathing capacity.

In the last decade, the CRISPR/Cas9 bacterial virus defense system has been adapted as a user-friendly, efficient, and precise method for targeted mutagenesis in eukaryotes. Though CRISPR/Cas9 has proven effective in a diverse range of organisms, it is still most often used to create mutant lines in lab-reared genetic model systems. However, one major advantage of CRISPR/Cas9 mutagenesis over previous gene targeting approaches is that its high efficiency allows the immediate generation of near-null mosaic mutants. This feature could potentially allow genotype to be linked to phenotype in organisms with life histories that preclude the establishment of purebred genetic lines; a group that includes the vast majority of vertebrate species. Of particular interest to scholars of early vertebrate evolution are several long-lived and slow-maturing fishes that diverged from two dominant modern lineages, teleosts and tetrapods, in the Ordovician, or before. These early-diverging or “basal” vertebrates include the jawless cyclostomes, cartilaginous fishes, and various non-teleost ray-finned fishes. In addition to occupying critical phylogenetic positions, these groups possess combinations of derived and ancestral features not seen in conventional model vertebrates, and thus provide an opportunity for understanding the genetic bases of such traits. Here we report successful use of CRISPR/Cas9 mutagenesis in one such non-teleost fish, sterlet Acipenser ruthenus, a small species of sturgeon. We introduced mutations into the genes Tyrosinase, which is needed for melanin production, and Sonic hedgehog, a pleiotropic developmental regulator with diverse roles in early embryonic patterning and organogenesis. We observed disruption of both loci and the production of consistent phenotypes, including both near-null mutants’ various hypomorphs. Based on these results, and previous work in lamprey and amphibians, we discuss how CRISPR/Cas9 F0 mutagenesis may be successfully adapted to other long-lived, slow-maturing aquatic vertebrates and identify the ease of obtaining and injecting eggs and/or zygotes as the main challenges.

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Mesalina are small lacertid lizards occurring in the Saharo-Sindian deserts from North Africa to the east of the Iranian plateau. Earlier phylogenetic studies indicated that there are several species complexes within the genus and that thorough taxonomic revisions are needed. In this study, we aim at resolving the phylogeny and taxonomy of the M. brevirostris species complex distributed from the Middle East to the Arabian/Persian Gulf region and Pakistan. We sequenced three mitochondrial and three nuclear gene fragments, and in combination with species delimitation and species-tree estimation, we infer a time-calibrated phylogeny of the complex. The results of the genetic analyses support the presence of four clearly delimited species in the complex that diverged approximately between the middle Pliocene and the Pliocene/Pleistocene boundary. Species distribution models of the four species show that the areas of suitable habitat are geographically well delineated and nearly allopatric, and that most of the species have rather divergent environmental niches.Morphological characters also confirm the differences between the species, although 650 | ŠMÍD et al. |ŠMÍD et al. ARCHIVED DATAAll alignments, phylogenetic trees, distribution records used for the SDMs, and photographs of all name-bearing type specimens of all the species and of all other examined material were deposited in MorphoBank (project 2355; www. morphobank.org).

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The northern pike, Esox lucius, is one of the largest temperate freshwater apex predators with a characteristic morphology: an elongated body with pelvic, dorsal, and anal fins located at the rear as a functional feature to sprint predation. However, the typical pike character is its head, which is characterized by a long, flattened snout, a well‐armed mouth with numerous teeth, and large eyes characteristic of shallow water visual predators. Although the northern pike is becoming increasingly popular as a model system for ecology and evolutionary research, a detailed staging table has not yet been reported. In this study, we report the first comprehensive staging table for the northern pike, spanning from the one‐cell stage to the freely‐swimming juvenile stage. In addition to classical embryological descriptions, we use a DAPI staining to distinguish individual cells and embryonic structures during the early development. This dataset, in combination with the genomic and transcriptomic resources already available, serves as a foundation for in‐depth mechanistic studies dealing with development using this species.