Phylogeny

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Xiphosurid evolution through the Palaeozoic era, showing representative genera.
(Figure by Anderson and Selden. Used with permission from Lyall Anderson.)

This phylogenetic tree shows the hypothesised evolutionary relationship of xiphosuird forms. The solid thick black lines represent fossil occurences, while the white lines represent ghost lineages (infered presence based on divergence time). The ancestral order to the Xiphosura are the Synziphosura, originating in the Early Silurian. Xiphosurids are thought to have evolved from the last and most advanced Synziphosurid called Kasibelinurus during the End Devonian. The extant family Limulinae evolved during the Triassic and continues to the present day. The Xiphosura are a sub-phylum within the Chelicerata, as are the now extinct Eurypterida. Cladistic analysis places the Eurypterids as a possible ancestor to the basal Synziphosurida.

Cladistic analysis places Lemoneites as the sister taxon to all true Chelicerata and the probable ancestor to the Xiphosura (Anderson and Seldon, 1997). However recent re-evaluation of the phylogenetic relationship based on Lemoneites morphology suggests a non-arthropod affinity thus excluding Lemoneites from the xiphosuran phylogeny (Moore and Braddy, 2005). The ghost range of Buriodes within the synziphosurines actually represents the occurene of Venustulus therefore making Venustulus waukeshaensis the oldest synziphosurine. Lemoneites is placed as a stem group of the Glyptocystitid.

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Author: Andrew Przewieslik
Last updated: 21/11/05
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