A consolidated phylogeny of snail-eating snakes (Serpentes, Dipsadini), with the description of five new species from Colombia, Ecuador, and Panama.

A molecular phylogeny of the Neotropical snail-eating snakes (tribe Dipsadini Bonaparte, 1838) is presented that includes 60 of the 133 species currently recognized. There is morphological and phylogenetic support for four new species of Sibon Fitzinger, 1826 and one of Dipsas Laurenti, 1768, which are described here based on their unique combination of molecular, meristic, and color pattern characteristics. PlesiodipsasHarvey et al., 2008 is designated as a junior synonym of Dipsas and additional evidence is presented to support the transfer of the genus Geophis Wagler, 1830 to the tribe Dipsadini. Two of the subspecies of S.nebulatus (Linnaeus, 1758) are elevated to full species status. Insight into additional undescribed cryptic diversity within the S.nebulatus species complex is provided. Evidence that supports the existence of an undescribed species previously confused with D.temporalis is provided, as well as the first country record of S.ayerbeorum Vera-Pérez, 2019 in Ecuador with a comment on the ontogenetic variation of the latter. Finally, photographs of Colombian, Ecuadorian, and Panamanian snail-eating snakes are provided.

Plicidentine and the repeated origins of snake venom fangs.

Snake fangs are an iconic exemplar of a complex adaptation, but despite striking developmental and morphological similarities, they probably evolved independently in several lineages of venomous snakes. How snakes could, uniquely among vertebrates, repeatedly evolve their complex venom delivery apparatus is an intriguing question. Here we shed light on the repeated evolution of snake venom fangs using histology, high-resolution computed tomography (microCT) and biomechanical modelling. Our examination of venomous and non-venomous species reveals that most snakes have dentine infoldings at the bases of their teeth, known as plicidentine, and that in venomous species, one of these infoldings was repurposed to form a longitudinal groove for venom delivery. Like plicidentine, venom grooves originate from infoldings of the developing dental epithelium prior to the formation of the tooth hard tissues. Derivation of the venom groove from a large plicidentine fold that develops early in tooth ontogeny reveals how snake venom fangs could originate repeatedly through the co-option of a pre-existing dental feature even without close association to a venom duct. We also show that, contrary to previous assumptions, dentine infoldings do not improve compression or bending resistance of snake teeth during biting; plicidentine may instead have a role in tooth attachment.

Descrição de uma nova espécie de serpente do gênero Tantilla Girard in Baird and Girard, 1853 (Colubridae: Colubrinae) do sul do Brasil

The genus Tantilla comprises 66 species, being one of the most diverse genera of snakes of the New World. In Brazil, there are two recognized species, T. boipiranga and T. melanocephala. The latter has the largest geographical distribution occurring from Guatemala to northern Argentina and Uruguay, as well as the islands of Trinidad and Tobago, Mustique Island, and the Islands of Saint Vincent Grenadines and Granada. T. melanocephala still presents a high degree of variation in coloration and general morphometry of the body. Therefore, a taxonomic revision of the T. melanocephala complex was carried out, with follicular characters, coloration and general morphometry of the 169 specimens being analyzed. A population of Tantilla was found, which is distributed through the southern Brazil, presented here as a new species. T. sp. n. is immediately distinguishable from the T. melanocephala complex by the presence of a blackish and broadened cephalic hood, covering a large part of the dorsum of the head and extending continuously to the inner scales; and presence of a longitudinal, blackened and diffuse paraventral band, later denser in the trunk. Although T. sp. n. is recognizable, there are populations along the distribution of T. melanocephala that, even though they have distinct colorations, are difficult to distinguish because there is a great overlap of meristic characters, which may mean the existence of cryptic diversity within this taxon. Finally, studies combining morphological and molecular evidences should be developed in order to test the hypothesis of cryptic diversity and elucidate the taxonomic relationships between the possible species of this complex.

O gênero Tantilla compreende 66 espécies, sendo um dos gêneros mais diversos de serpentes do Novo Mundo. No Brasil, há duas espécies reconhecidas, T. boipiranga e T. melanocephala. A última possui a maior distribuição geográfica ocorrendo desde a Guatemala, até o norte da Argentina e Uruguai, além das ilhas de Trinidad e Tobago, Ilha Mustique, e Ilhas de São Vicente Granadinas e Granada. T. melanocephala ainda apresenta alto grau de variação na coloração e morfometria geral do corpo. Diante disso, conduziu-se uma revisão taxonômica do complexo T. melanocephala, analisando-se caracteres de folidose, coloração e morfometria geral do corpo de 169 espécimes e descobriu-se uma população de Tantilla, que se distribui pelas áreas de campo do sul do Brasil, apresentada aqui como uma nova espécie. T. sp. n. é imediatamente distinguível do complexo T. melanocephala pela presença de capuz cefálico enegrecido e amplo, cobrindo grande parte do dorso da cabeça e estendendo-se continuamente até as escamas internasais; e presença de faixa paraventral longitudinal, enegrecida e difusa, mais adensada posteriormente no tronco. Embora T. sp. n. seja reconhecível, há populações ao longo da distribuição de T. melanocephala que, mesmo apresentando colorações distintas, são difíceis de distinguir porque há grande sobreposição de caracteres merísticos, o que pode significar a existência de diversidade críptica dentro desse táxon. Finalmente, estudos combinando evidências morfológicas e moleculares devem ser desenvolvidos, afim de testar a hipótese de diversidade críptica e elucidar as relações taxonômicas entre as possíveis espécies deste complexo.

Fossil snakes (Squamata, Serpentes) from the tar pits of Venezuela: taxonomic, palaeoenvironmental, and palaeobiogeographical implications for the North of South America during the Cenozoic/Quaternary boundary.

BACKGROUND: Tar seep deposits in South America historically are well-known for their rich record of fossil mammals, contrasting with only a few formal reports of reptile remains. Here we report a new snake fauna recovered from two tar pits from Venezuela. The fossil remains come from two localities: (a) El Breal de Orocual, which comprises an inactive tar seep estimated to be Plio/Pleistocene in age; and (b) Mene de Inciarte, an active surface asphalt deposit with an absolute age dating to the late Pleistocene. METHODS: The taxonomic identity of all specimens was assessed via consultation of the relevant literature and comparison with extant specimens. The taxonomic assignments are supported by detailed anatomical description. RESULTS: The Mene de Inciarte snake fauna comprises vertebral remains identified as the genus Epicrates sp. (Boidae), indeterminate viperids, and several isolated vertebrae attributable to "Colubridae" (Colubroidea, sensu Zaher et al., 2009). Amongst the vertebral assemblage at El Breal de Orocual, one specimen is assigned to the genus Corallus sp. (Boidae), another to cf. Micrurus (Elapidae), and several others to "Colubrids" (Colubroides, sensu Zaher et al., 2009) and the Viperidae family. CONCLUSIONS: These new records provide valuable insight into the diversity of snakes in the north of South America during the Neogene/Quaternary boundary. The snake fauna of El Breal de Orocual and Mene de Inciarte demonstrates the presence of Boidae, Viperidae, "colubrids", and the oldest South American record of Elapidae. The presence of Corallus, Epicrates, and viperids corroborates the mosaic palaeoenvironmental conditions of El Breal de Orocual. The presence of Colubroides within both deposits sheds light on the palaeobiogeographical pattern of caenophidians snake colonization of South America and is consistent with the hypothesis of two episodes of dispersion of Colubroides to the continent.

Effectiveness of phylogenomic data and coalescent species-tree methods for resolving difficult nodes in the phylogeny of advanced snakes (Serpentes: Caenophidia).

Next-generation genomic sequencing promises to quickly and cheaply resolve remaining contentious nodes in the Tree of Life, and facilitates species-tree estimation while taking into account stochastic genealogical discordance among loci. Recent methods for estimating species trees bypass full likelihood-based estimates of the multi-species coalescent, and approximate the true species-tree using simpler summary metrics. These methods converge on the true species-tree with sufficient genomic sampling, even in the anomaly zone. However, no studies have yet evaluated their efficacy on a large-scale phylogenomic dataset, and compared them to previous concatenation strategies. Here, we generate such a dataset for Caenophidian snakes, a group with >2500 species that contains several rapid radiations that were poorly resolved with fewer loci. We generate sequence data for 333 single-copy nuclear loci with ∼100% coverage (∼0% missing data) for 31 major lineages. We estimate phylogenies using neighbor joining, maximum parsimony, maximum likelihood, and three summary species-tree approaches (NJst, STAR, and MP-EST). All methods yield similar resolution and support for most nodes. However, not all methods support monophyly of Caenophidia, with Acrochordidae placed as the sister taxon to Pythonidae in some analyses. Thus, phylogenomic species-tree estimation may occasionally disagree with well-supported relationships from concatenated analyses of small numbers of nuclear or mitochondrial genes, a consideration for future studies. In contrast for at least two diverse, rapid radiations (Lamprophiidae and Colubridae), phylogenomic data and species-tree inference do little to improve resolution and support. Thus, certain nodes may lack strong signal, and larger datasets and more sophisticated analyses may still fail to resolve them.