The phylogeny of arachnomorph arthropods and the origin of the Chelicerata

  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},
  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… 
Revised systematics of Palaeozoic ‘horseshoe crabs’ and the myth of monophyletic Xiphosura
A number of other characters, including the form of the chelicerae and appendage VII, indicate that xiphosurans may be paraphyletic with respect to a clade consisting of chasmataspidids, eurypterids, and arachnids.
Geological history and phylogeny of Chelicerata.
  • J. Dunlop
  • Geology, Biology
    Arthropod structure & development
  • 2010
Sanctacaris uncata: the oldest chelicerate (Arthropoda)
Topology indicates that many purported chelicerate features, such as lamellar gills, and a differentiated posterior abdomen evolved sequentially in the chelicerates stem-lineage.
New Phylogenetic Insights into the Cambrian Radiation of Arachnomorph Arthropods
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.
New ideas about the euchelicerate stem-lineage
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.
The phylogeny of aglaspidid arthropods and the internal relationships within Artiopoda
The phylogenetic position of aglaspidid arthropod groups makes them good outgroup candidates for analysing the internal relationships within the groups that form Trilobitomorpha, and the new clade “Vicissicaudata” is proposed to encompass these arthropods, which are characterized by a differentiated posterior region.
The affinities of the cosmopolitan arthropod Isoxys and its implications for the origin of arthropods
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.
A Parvancorina-like arthropod from the Cambrian of South China
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
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).


Evolution and systematics of the Chelicerata
After approximately 40 years of discussion about the question whether the Arthropoda are a monophyletic or a paraphyletic group, or even a polyphyletic assemblage of unrelated taxa, most
The early history and phylogeny of the chelicerates
When fossil taxa are considered, the limits of the Chelicerata become less well constrained, especially true of various problematic arthropods: fossils such as aglaspidids, chasmataspids, Sanctacaris Briggs and Collins, 1988 and other Burgess Shale-type arthropODs.
A cladistic analysis of the 11 Recent arachnid orders suggests that Arachnida is monophyletic and composed of two principal lineages, Micrura and Dromopoda.
Morphological phylogenetics of the sea spiders (Arthropoda: Pycnogonida)
The reduction of the chelifores, palps and ovigers — shown independently within each of the clades as parallel evolution events — challenges the assumption of a gradual mode of reduction within the Pycnogonida, according to analysis of unordered vs ordered characters.
The Phylogeny of the Extant Chelicerate Orders
The phylogeny of the extant chelicerate orders is examined in the light of morphological and molecular evidence, with the placement of solifugids and the status of the pedipalps responsible for most disagreement fairly robust to variation in analysis parameters.
Relationships of Cambrian Arachnata and the systematic position of Trilobita
Reweighted characters favor Trilobita and Helmetiida as closest relatives, with Petalopleura and then Naraoiidae as sister groups.
The Early Radiation and Relationships of the Major Arthropod Groups
Cladistic analysis of characters of Cambrian and living representatives (excluding Uniramia) shows that trilobites and chelicerates are relatively advanced compared with "crustaceans," and there are doubts whether the latter constitute a national group.
Cladistic analysis of the Early Cambrian olenelloid trilobites
It is likely that rates of speciation in trilobites may have been two to three times higher in the Early Cambrian than in the mid Paleozoic, and two new genera are recognized herein, Fritzolenellus and LochmanolenellUS.
A Larval Sea Spider (Arthropoda: Pycnogonida) from the Upper Cambrian ‘orsten’ of Sweden, and the Phylogenetic Position of Pycnogonids
The pre‐cheliceral limbs in this fossil support traditional morphological studies in which the chelicera represent the second head appendage corresponding to the crustacean ‘second antennae’, and contradict recent data based on homeobox genes implying that theChelicerae are the first (a1) head appendages homologous with crustaceans first antennae.
The place of tardigrades in arthropod evolution
The phylum Tardigrada is an engaging but enigmatic group composed of minute metazoans with four pairs of stubby lobopodous appendages that share important derived characters with arthropods but, as a consequence, the phylogenetic position of the taxon remains uncertain.