Morphological analysis of phylogenetic relationships among extant rhynchonellide brachiopods

Abstract

Rhynchonellida is the stratigraphically oldest and phylogenetically most basal of the extant rhynchonelliform brachiopod orders, yet phylogenetic relationships among rhynchonellides are poorly known. The fourteen named rhynchonellide superfamilies (four of which have extant representatives) were defined primarily on the basis of features of the dorsal cardinalia, particularly crural morphology, but their homology and polarity have not been investigated rigorously. Superfamily monophyly is unclear, as is the evolution of several distinctive rhynchonellide morphological features, such as crura.The purpose of this study is to investigate the phylogenetic relationships among extant rhynchonellide genera using skeletal characters, and to compare the results with the current classification, elucidating the evolution of morphological features in the process. We completed parsimony-based and Bayesian analyses using fifty-eight characters of the interior and exterior of the shell that vary among the nineteen extant genera. Our results are readily interpretable with respect to the classification, and indicate that Hemithiridoidea, Dimerelloidea, and (in some analyses) Pugnacoidea appear to be monophyletic. Species classified in Dimerelloidea and Pugnacoidea, and in certain cases Hemithiridoidea, each form derived subclades that evolve from within a paraphyletic Norelloidea at the base of each subclade. Raduliform crura appear to be the most basal, phylogenetically; five other crural morphologies evolve from the raduliform state. However, morphological characters currently uniting genera in rhynchonellide superfamilies are not clearly diagnostic and exhibit a relatively high degree of homoplasy overall, suggesting that consistency with the classification may be based on a false sense of confidence in rhynchonellide morphology to clearly elucidate evolutionary relationships. Published molecular phylogenetic hypotheses conflict with the morphological topologies, further supporting this possibility.The evolutionary trends among diagnostic characters of Recent rhynchonellides appear to reflect successive juvenilization in adult morphology in several subclades, suggesting that heterochrony may have played an important role in the evolution of the group.

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

“…A comprehensive cladistic analysis shows congruence between cladistic relationships of the extant taxa and the four crown‐group superfamilies (Schreiber, Bitner & Carlson, ), but such congruence is expected because most cladistic characters are dependent on shell morphology (see Discussion). By contrast, an rDNA gene tree shows complete disagreement between molecular clades and superfamily affiliations (Cohen & Bitner, : figs 2, 3; Schreiber, Bitner & Carlson, ), and suggests that some inferences of rhynchonellide evolutionary relationships from morphology (Savage et al ., ) may have involved: (1) the misidentification of ancestral and descendant character states (i.e. mistaken polarity determination); and/or (2) mistaken assessment of character homology, caused by limited ability to recognize character states that originated independently, i.e.…”

“…The treatise recognizes that the morphological classification suffers from a dearth of non‐homoplasious and clear‐cut morphological characters (Savage et al ., , p. 1027), and a later study of the main internal shell structures, the crura, and microstructural patterns of the secondary layer (Manceñido & Motchurova‐Dekova, ), also suggests that the classification of Rhynchonellida requires revision based on multiple morphological characters. In addition, it is the only case (so far) that permits comparison of the rDNA gene tree with two different forms of morphology‐based systematics: (1) the treatise classification (Savage et al ., ); and (2) a comprehensive phylogenetic analysis involving 58 characters from 25 fossil out‐group and Recent in‐group taxa (Schreiber et al ., ). Compared with the treatise classification ‘the molecular phylogeny … disagrees dramatically with the morphology‐based classification; the four specimens in clade A1 belong to all four extant superfamilies and no single clade contains members of any one superfamily’ (Cohen & Bitner, : p. 214).…”

The Evolution of Brachiopoda

“…Of course, such a diagram, with orders as terminal taxa, implies the monophyly of each order, which we know does not obtain for many orders. For some orders (Rhynchonellida), the degree of incongruity of morphological results (Schreiber et al 2013) and molecular results (Cohen & Bitner 2013), even among only the few species extant, is worrisome. For others (Terebratulida), the agreement appears to be greater (Cohen 2007;S.J.…”

A preliminary phylogenetic study of late Palaeozoic spiriferoid brachiopods using cladistic and Bayesian approaches

“…However, the model-based methodologies, particularly those based on maximum likelihood and Bayesian inference, recently started to use morphological data for defining the phylogeny (Wagner, 1998;Lewis, 2001). With the development of computational techniques and new software the actual application has been accomplished in a few recent studies, including studies on fossil brachiopods (e.g., Schreiber et al, 2013;Wright and Stigall, 2013). The present study Page 7 of 41 A c c e p t e d M a n u s c r i p t 7 constructs phylogenetic trees through both cladistics and Bayesian phylogenetic inference and then compares the results.…”