Caenophidian snakes include the file snake genus Acrochordus and advanced colubroidean snakes that radiated mainly during the Neogene. Although caenophidian snakes are a well-supported clade, their ...inferred affinities, based either on molecular or morphological data, remain poorly known or controversial. Here, we provide an expanded molecular phylogenetic analysis of Caenophidia and use three non-parametric measures of support-Shimodaira-Hasegawa-Like test (SHL), Felsentein (FBP) and transfer (TBE) bootstrap measures-to evaluate the robustness of each clade in the molecular tree. That very different alternative support values are common suggests that results based on only one support value should be viewed with caution. Using a scheme to combine support values, we find 20.9% of the 1265 clades comprising the inferred caenophidian tree are unambiguously supported by both SHL and FBP values, while almost 37% are unsupported or ambiguously supported, revealing the substantial extent of phylogenetic problems within Caenophidia. Combined FBP/TBE support values show similar results, while SHL/TBE result in slightly higher combined values. We consider key morphological attributes of colubroidean cranial, vertebral and hemipenial anatomy and provide additional morphological evidence supporting the clades Colubroides, Colubriformes, and Endoglyptodonta. We review and revise the relevant caenophidian fossil record and provide a time-calibrated tree derived from our molecular data to discuss the main cladogenetic events that resulted in present-day patterns of caenophidian diversification. Our results suggest that all extant families of Colubroidea and Elapoidea composing the present-day endoglyptodont fauna originated rapidly within the early Oligocene-between approximately 33 and 28 Mya-following the major terrestrial faunal turnover known as the "Grande Coupure" and associated with the overall climate shift at the Eocene-Oligocene boundary. Our results further suggest that the caenophidian radiation originated within the Caenozoic, with the divergence between Colubroides and Acrochordidae occurring in the early Eocene, at ~ 56 Mya.
Display omitted
•We generated a molecular phylogeny for 79% species of vipers.•We provide divergence time estimates between lineages.•Vipers are characterized by two distinct diversification ...regimes.•Speciation rates rapidly increased in a sub-clade of pit vipers.
Snakes of the cosmopolitan family Viperidae comprise around 329 venomous species showing a striking heterogeneity in species richness among lineages. While the subfamily Azemiopinae comprises only two species, 70% of all viper species are arranged in the subfamily Crotalinae or the “pit vipers”. The radiation of the pit vipers was marked by the evolution of the heat-sensing pits, which has been suggested to be a key innovation for the successful diversification of the group. Additionally, only crotalines were able to successfully colonize the New World. Here, we present the most complete molecular phylogeny for the family to date that comprises sequences from nuclear and mitochondrial genes representing 79% of all living vipers. We also investigated the time of divergence between lineages, using six fossils to calibrate the tree, and explored the hypothesis that crotalines have undergone an explosive radiation. Our phylogenetic analyses retrieved high support values for the monophyly of the family Viperidae, subfamilies Viperinae and Crotalinae, and 22 out of 27 genera, as well as well-supported intergeneric relationships throughout the family. We were able to recover a strongly supported sister clade to the New World pit vipers that comprises Gloydius, Ovophis, Protobothrops and Trimeresurus gracilis. Our results agree in many aspects with other studies focusing on the phylogenetics of vipers, but we recover new relationships as well. Despite the addition of new sequences we were not able to resolve some of the poor supported relationships previously suggested. Time of divergence estimates suggested that vipers started to radiate around the late Paleocene to middle Eocene with subfamilies most likely dating back to the Eocene. The invasion of the New World might have taken place sometime close to the Oligocene/Miocene boundary. Diversification analyses suggested a shift in speciation rates during the radiation of a sub-clade of pit vipers where speciation rates rapidly increased but slowed down toward the present. Thus, the evolution of the loreal pits alone does not seem to explain their explosive speciation rates. We suggest that climatic and geological changes in Asia and the invasion of the New World may have also contributed to the speciation shift found in vipers.
A new notosuchian crocodyliform from the Late Cretaceous Bauru Group found in the southeastern State of São Paulo (Brazil) is described here. The new taxon, Caipirasuchus stenognathus, is referred as ...a new species of the recently erected genus Caipirasuchus within the clade Sphagesauridae based on a phylogenetic analysis of basal mesoeucrocodylians. Caipirasuchus stenognathus is represented by an almost complete skull and lower jaw that has autapomorphic characters that distinguish it from other species of Sphagesauridae. These autapomorphies include: maxilla forming part of the orbital margin (absence of lacrimal-jugal contact), nasal with smooth depressions on the posterior region close to the contact with the maxilla and lacrimal, postorbital with posterior palpebral facet that extends posteriorly underneath the ear-flap groove, and a distinct anterior process of the medial flange of the retroarticular process. Additionally, the new taxon lacks autapomorphic features described in other sphagesaurids. The phylogenetic analysis results in a monophyletic genus Caipirasuchus, that is the sister group of a clade fomed by Sphagesaurus huenei, Caryonosuchus pricei, and Armadillosuchus arrudai. Sphagesaurids also include a basal clade formed by Adamantinasuchus navae and Yacarerani boliviensis. Other notosuchian taxa, such as Mariliasuchus amarali, Labidiosuchus amicum, Notosuchus terrestris, and Morrinhosuchus luziae are successive sister taxa of Sphagesauridae, forming a clade of advanced notosuchians that are restricted to the Late Cretaceous of South America. These results contrast with most previous phylogenetic hypotheses of the group that depicted some members of Sphagesauridae as more closely related to baurusuchids, or found Asian (e.g., Chimaerasuchus) or African (Malawisuchus, Pakasuchus) forms nested within advanced notosuchians that are, according to our analysis, endemic of the Late Cretaceous of South America.
Factors driving the spatial configuration of centres of endemism have long been a topic of broad interest and debate. Due to different eco‐evolutionary processes, these highly biodiverse areas may ...harbour different amounts of ancient and recently diverged organisms (paleo‐ and neo‐endemism, respectively). Patterns of endemism still need to be measured at distinct phylogenetic levels for most clades and, consequently, little is known about the distribution, the age and the causes of such patterns. Here we tested for the presence of centres with high phylogenetic endemism (PE) in the highly diverse Neotropical snakes, testing the age of these patterns (paleo‐ or neo‐endemism), and the presence of PE centres with distinct phylogenetic composition. We then tested whether PE is predicted by topography, by climate (seasonality, stability, buffering and relictualness), or biome size. We found that most areas of high PE for Neotropical snakes present a combination of both ancient and recently diverged diversity, which is distributed mostly in the Caribbean region, Central America, the Andes, the Atlantic Forest and on scattered highlands in central Brazil. Turnover of lineages is higher across Central America, resulting in more phylogenetically distinct PE centres compared to South America, which presents a more phylogenetically uniform snake fauna. Finally, we found that elevational range (topographic roughness) is the main predictor of PE, especially for paleo‐endemism, whereas low paleo‐endemism levels coincide with areas of high climatic seasonality. Our study highlights the importance of mountain systems to both ancient and recent narrowly distributed diversity. Mountains are both museums and cradles of snake diversity in the Neotropics, which has important implications for conservation in this region.
Advanced titanosaurian sauropods, such as nemegtosaurids and saltasaurids, were diverse and one of the most important groups of herbivores in the terrestrial biotas of the Late Cretaceous. However, ...little is known about their rise and diversification prior to the Late Cretaceous. Furthermore, the evolution of their highly-modified skull anatomy has been largely hindered by the scarcity of well-preserved cranial remains. A new sauropod dinosaur from the Early Cretaceous of Brazil represents the earliest advanced titanosaurian known to date, demonstrating that the initial diversification of advanced titanosaurians was well under way at least 30 million years before their known radiation in the latest Cretaceous. The new taxon also preserves the most complete skull among titanosaurians, further revealing that their low and elongated diplodocid-like skull morphology appeared much earlier than previously thought.
The present work describes a new species of Baurusuchidae from Upper Cretaceous sediments of the Bauru Basin, and provides the first complete postcranial description for the family. Many postcranial ...features observed in the new species are also present in other notosuchian taxa, and are thus considered plesiomorphic for the genus. These are: long cervical neural spines; robust deltopectoral crest of the humerus; large proximal portion in the radiale that contacts the ulna; ulnare anterior distal projection; supra-acetabular crest well developed laterally; post-acetabular process posterodorsally deflected; presence of an anteromedial crest in the femur; fourth trocanter of femur posteriorly positioned; tibia with a laterally curved shaft; calcaneum tuber posteroventrally oriented; osteoderms ornamented with grooves and imbricated in the tail. On the other hand, we found the following sacral and carpal features to be unique among all mesoeucrocodylians analyzed: transverse processes of sacral vertebrae dorsolaterally deflected; presence of a longitudinal crest in the lateral surface of sacral vertebrae; pisiform carpal with a condyle-like surface. The majority of these cited features corroborates a cursorial locomotion for the new species described in the present study, suggesting that members of the family Baurusuchidae were also cursorial species.
We present a molecular phylogenetic analysis of caenophidian (advanced) snakes using sequences from two mitochondrial genes (12S and 16S rRNA) and one nuclear (c-mos) gene (1681 total base pairs), ...and with 131 terminal taxa sampled from throughout all major caenophidian lineages but focussing on Neotropical xenodontines. Direct optimization parsimony analysis resulted in a well-resolved phylogenetic tree, which corroborates some clades identified in previous analyses and suggests new hypotheses for the composition and relationships of others. The major salient points of our analysis are: (1) placement of Acrochordus, Xenodermatids, and Pareatids as successive outgroups to all remaining caenophidians (including viperids, elapids, atractaspidids, and all other "colubrid" groups); (2) within the latter group, viperids and homalopsids are sucessive sister clades to all remaining snakes; (3) the following monophyletic clades within crown group caenophidians: Afro-Asian psammophiids (including Mimophis from Madagascar), Elapidae (including hydrophiines but excluding Homoroselaps), Pseudoxyrhophiinae, Colubrinae, Natricinae, Dipsadinae, and Xenodontinae. Homoroselaps is associated with atractaspidids. Our analysis suggests some taxonomic changes within xenodontines, including new taxonomy for Alsophis elegans, Liophis amarali, and further taxonomic changes within Xenodontini and the West Indian radiation of xenodontines. Based on our molecular analysis, we present a revised classification for caenophidians and provide morphological diagnoses for many of the included clades; we also highlight groups where much more work is needed. We name as new two higher taxonomic clades within Caenophidia, one new subfamily within Dipsadidae, and, within Xenodontinae five new tribes, six new genera and two resurrected genera. We synonymize Xenoxybelis and Pseudablabes with Philodryas; Erythrolamprus with Liophis; and Lystrophis and Waglerophis with Xenodon.
South American racers of the tribe Philodryadini are a widespread and diverse group of Neotropical snakes with a complex taxonomic and systematic history. Recent studies failed to present a robust ...phylogenetic hypothesis for the tribe, mainly due to incomplete taxon sampling. Here we provide the most extensive molecular phylogenetic analysis of Philodryadini available so far, including 20 species (83% of the known diversity) from which six were not sampled previously. Our results reveal that Philodryadini is not monophyletic, but instead includes a central Andean clade formed by Philodryas simonsii, P. tachymenoides, and P. amaru, and a southern and cis-Andean clade including all remaining philodryadines. This discovery requires resurrection of two genera as well as erection of a new tribe of Xenodontinae for the central Andean clade. Within the southern and cis-Andean radiation, our analyses resolve a basal dichotomy separating two main lineages: Clade A, containing the Common Green Racers P. laticeps and P. viridissima and the South American Vine snakes P. georgeboulengeri and P. argentea; and Clade B, including the remaining species of Philodryas sensu stricto. We resurrect the genera Chlorosoma and Xenoxybelis to better represent the monophyly of lineages within the southern and cis-Andean clade.
PDF
