Crinoid phylogeny: new interpretation of the main Permo ‐Triassic divergence, comparisons with echinoids and brachiopods, and EvoDevo interpretations of major morphological variations

An alignment of nuclear and mitochondrial gene sequences (1529 data columns from three genes: nuclear‐encoded 28S ribosomal DNA, mitochondrial 16S rDNA, and cytochrome oxidase subunit 1) from 120 specimens representing a wide selection of extant crinoids is used in Bayesian relaxed‐clock analyses to construct the maximum clade credibility tree and to locate the root. This tree, and its root position, largely agree with those previously published on the basis of mid‐point and outgroup rooting, and, using a likelihood ratio test, we find that our independently aligned data do not depart significantly from a strict molecular clock. Our tree, similar to those published previously, shows a basal split into two main clades but, unlike previous reports, we identify a phenotypic basis for the split and name the clades accordingly, ‘Stalked and quasi‐stalked’ (SqS) and ‘Stalked but facultatively unstalked’ (SfU), with the latter corresponding to the ‘comatulids’. There is some correspondence between clades and morphologically‐defined Linnean categories in the SqS clade (e.g. the family Hyocrinidae corresponds to a clade). However, there is almost no correspondence between them in the SfU clade, within which we abandon Linnean names and instead use the letters A to E, suggesting, as previously noted, that considerable morphology‐based taxonomic oversplitting has occurred, such that critical revision that takes account of molecular results is overdue. The distinc...
Source: Biological Journal of the Linnean Society - Category: Research Authors: Tags: Research Article Source Type: research