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Brief review of the stylophoran debate
Author(s) -
Ruta Marcello
Publication year - 1999
Publication title -
evolution and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.651
H-Index - 78
eISSN - 1525-142X
pISSN - 1520-541X
DOI - 10.1046/j.1525-142x.1999.99008.x
Subject(s) - synapomorphy , biology , monophyly , echinoderm , paleontology , clade , evolutionary biology , phylum , zoology , phylogenetics , biochemistry , gene , bacteria
The “calcichordate” theory interprets an extinct group of calcite‐plated invertebrates, the stylophorans, as chordates. In this theory, cornute stylophorans are interpreted as stem chordates, whereas mitrate stylophorans are primitive members of the acraniates, tunicates, and craniates. However, this theory discounts major synapomorphies between cornutes and mitrates. These groups constitute a natural, monophyletic group which is here argued to lie within the echinoderm radiation. The “calcichordate” theory is, therefore, rejected because it relies on assumption‐driven hypotheses of character transformation which are supported by ambiguous, poor, or missing fossil evidence. Stylophorans may lie at the base of the echinoderm clade and primitively lack pentameral symmetry, therefore casting light on the near‐ancestral body organization of the phylum.