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Chasmataspidids are a group of Early Paleozoic (Middle Ordovician-Middle Devonian)chelicerates defined by an apparently unique opisthosomal tagmosis consisting of a microtergite, a three-segmented fused buckler, and a nine-segmented postabdomen. Although the number of known chasmataspidid species increased by half during the past decade, the group has not been a subject of detailed phylogenetic analysis, and its placement within Chelicerata is uncertain. Though recent analyses that include chasmataspidids support a monophyletic Chasmataspidida as sister to Sclerophorata (Eurypterida and Arachnida), few have sampled more than three of the 14 currently recognized species. Previous workers have suggested chasmataspidids may be a polyphyletic or paraphyletic group, or that chasmataspidids may resolve as the sister taxon to eurypterids, or even as a clade within Eurypterida. Without a broader sampling of chasmataspidids it is not possible to adequately test these various hypotheses, while a robust phylogenetic framework in necessary for understanding macroevolutionary and biogeographic trends within the group. Chasmataspidids also represent the earliest preserved euchelicerate in the fossil record, with Chasmataspis dated to approximately 478 million years ago, and as such its phylogenetic position in relation to other euchelicerates has implications for the divergence times of those clades. We present a new phylogenetic matrix comprising 81 characters coded for every currently described chasmataspidid species, analysis of which under maximum parsimony and Bayesian inference results in concordant phylogenetic topologies. Chasmataspidida resolves as in most recent analyses as a monophyletic clade sister to Sclerophorata, indicating that Xiphosura, Chasmataspidida, and Sclerophorata likely diverged in the Early Ordovician. The analysis also supports a taxonomic revision within Chasmataspidida; we propose dividing the clade into two superfamilies, with four constituent families. As part of this study the Silurian taxon Loganamaraspis was reevaluated and the morphology of appendage VI, previously considered to be retained as a walking limb, could not be ascertained.
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Towards rectifying limitations on species delineation in dusky salamanders (Desmognathus: Plethodontidae): An ecoregion-drainage sampling grid reveals additional cryptic clades
Dusky salamanders (Desmognathus) constitute a large, species-rich group within the family Plethodontidae, and though their systematic relationships have been addressed extensively, most studies have centered on particular species complexes and therefore offer only piecemeal phylogenetic perspective on the genus. Recent work has revealed Desmognathus to be far more clade rich—35 reciprocally monophyletic clades versus 22 recognized species—than previously imagined, results that, in turn, provide impetus for additional survey effort within clades and across geographic areas thus far sparsely sampled. We conceived and implemented a sampling regime combining level IV ecoregions and independent river drainages to yield a geographic grid for comprehensive recovery of all genealogically exclusive clades. We sampled over 550 populations throughout the distribution of Desmognathus in the eastern United States of America and generated mitochondrial DNA sequence data (mtDNA; 1,991 bp) for 536 specimens. A Bayesian phylogenetic reconstruction of the resulting haplotypes revealed forty-five reciprocally monophyletic clades, eleven of which have never been included in a comprehensive phylogenetic reconstruction, and an additional three not represented in any molecular systematic survey. Although general limitations associated with mtDNA data preclude new species delineation, we profile each of the 45 clades and assign names to 10 new clades (following a protocol for previous clade nomenclature). We also redefine several species complexes and erect new informal species complexes. Our dataset, which contains topotypic samples for nearly every currently recognized species and most synonymies, will offer a robust framework for future efforts to delimit species within Desmognathus.
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- Award ID(s):
- 1656111
- PAR ID:
- 10250791
- Date Published:
- Journal Name:
- Zootaxa
- Volume:
- 4734
- Issue:
- 1
- ISSN:
- 1175-5326
- Page Range / eLocation ID:
- 1 to 61
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.11646/zootaxa.4734.1.1
