Evolution of Biomineralization in Lophophorates

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Improved knowledge of the fossil record, combined with molecular trees describing the phylogenetic relationships between recent phyla, is gradually advancing our understanding of the evolution of biomineralized marine invertebrates. However, relationships between the three extant 'lophophorate' phyla - Brachiopoda, Bryozoa and Phoronida - have yet to be resolved, and the monophyletic status of Lophophorata has been called into question. Here, we review the phylogeny and biomineralization of lophophorates, along with some extinct groups that have been suggested to be lophophorates on the basis of skeletal structure and ultrastructure. We conclude that biomineralized skeletons are not homologous in lophophorates, the skeletons of brachiopods being plesiomorphic, whereas biomineralization in bryozoans is apomorphic and has evolved independently twice from soft-bodied, ctenostomegrade bryozoan ancestors. Phoronida nests within Brachiopoda, according to the molecular tree, and between two clades (rhynchonelliformeans and craniiformians) having calcareous shells, in which case stem-group phoronids would likely have possessed calcareous skeletons too. Both the solitary, vermiform Tentaculitoidea (OrdovicianJurassic) and the colonial, bryozoan-like Hederelloidea (Silurian-Permian) are here considered to be biomineralized stem-group phoronids. © The Palaeontological Association.


Biomineralization, Brachiopoda, Bryozoa, Hederelloidea, Phoronida, Phylogeny, Tentaculoidea