Congruence and conflict: case studies of morphotaxonomy versus rDNA gene tree phylogeny among articulate brachiopods (Brachiopoda: Rhynchonelliformea), with description of a new genus

Abstract

We present five case studies among articulate (rhynchonelliform) brachiopods, i.e. of Rhynchonellida, Cancellothyridoidea, Terebratuloidea, Dyscolioidea, Laqueoidea, and various terebratulids with modified long-loops, in an attempt to illustrate and better understand congruence and conflict between morpho-classification and rDNA-based molecular clade structure, having been prompted to address these issues by difficulties encountered when describing the newly collected brachiopod, Ebiscothyris bellonensis gen. et sp. nov. The five studies reveal dramatic conflict in the Rhynchonellida and Terebratuloidea/Dyscolioidea, good congruence in the Cancellothyridoidea and Laqueoidea, and fair congruence (albeit with weak phylogenetic signal) in the long-looped terebratulids. We suggest that the leading cause of the observed conflict lies in the use of inadequately specific morphological characters and morpho-classification. Phylogenetic systematic (cladistic) analyses of Rhynchonellida also conflict markedly with the rDNA gene tree, leading us to recognize that such analyses are not only conceptually circular (using morphological characters to assess a morphological classification) but also to propose that they are biased by the act of classification that necessarily precedes the identification of putatively homologous characters; when the prior classification does not reflect evolutionary history, phylogenetic analysis will do likewise. In addition, we propose that the brachiopod community has overlooked the significance of two sources of morphological homoplasy affecting brachiopod systematics: (1) the loss of co-adapted genomic complexes caused by mass extinctions at the end of the Permian; and (2) the pervasive consequences of developmental integration and constraint resulting from the integrated roles of the outer mantle epithelium in shell deposition and growth that underly the determination of form and the shell-based classification. © 2015 The Linnean Society of London