The phylogeny of arachnomorph arthropods and the origin of the Chelicerata

@article{Cotton2003ThePO,
  title={The phylogeny of arachnomorph arthropods and the origin of the Chelicerata},
  author={Trevor J. Cotton and Simon J. Braddy},
  journal={Transactions of the Royal Society of Edinburgh: Earth Sciences},
  year={2003},
  volume={94},
  pages={169 - 193}
}
  • Trevor J. Cotton, S. Braddy
  • Published 1 September 2003
  • Biology, Geography
  • Transactions of the Royal Society of Edinburgh: Earth Sciences
ABSTRACT A new hypothesis of the relationships between arachnomorph arthropods, and the origin of chelicerates, is presented based on a cladistic analysis of 34 taxa and 54 characters. The present study provides a detailed discussion of primary hypotheses of homology and includes a more complete range of terminal taxa than previous analyses. The analysis provides the first convincing synapomorphies for the Arachnomorpha, and suggests that the marrellomorphs are not arachnomorphs. The assignment… 
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Highly Influential Citations
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116 Citations

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Topology indicates that many purported chelicerate features, such as lamellar gills, and a differentiated posterior abdomen evolved sequentially in the chelicerates stem-lineage.
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The results of the cladistic analysis suggest that at least three distinct arachnomorph clades had diverged by the Middle Cambrian, and perhaps much earlier; the Utah genera can be referred to groups within one of these clades.
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In the scenario presented here euchelicerates did not lose (and indeed never had) long, sensory antennae, but probably evolved their chelicerae from a leg-like pair of uniramous appendages.
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The results indicate that Isoxys was indeed a monophyletic genus with all representatives united by the presence of an expansive dorsal shield with prominent antero- and posterolateral cardinal spines, and indicates that I soxys occupies a crucial role in arthropod evolution, resolving at the base of Arthropoda.
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A new species is reported here of the Cambrian arthropod Skania, which bears an exoskeleton that shares homologies with the Neoproterozoic organism Parvancorina and firmly establishes a Precambrian root for arthropods.
A glyptocystitid cystoid affinity for the putative stem group chelicerate (Arthropoda: Aglaspidida or Xiphosura) Lemoneites from the Ordovician of Texas, USA
TLDR
Cladistic analyses placed Lemoneites as “sister group to all other [eu]chelicerates . . . probably a common ancestor of Chelicerata”, as the possible ancestor of Xiphosura (Anderson & Selden 1997), or within a ‘chelicerate-allied’ clade of arachnomorph arthropods (Cotton & Braddy 2004).
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