Patterns of diversification and phylogenetic structure in the dorsolateral head musculature of Neotropical electric eels (Ostariophysi: Gymnotiformes), with a myological synonymy

Abstract

The present study offers a broad comparative analysis of the dorsolateral head musculature in the Gymnotiformes, with detailed descriptions and illustrations of the dorsolateral head muscles of 83 species representing combined all valid genera. Results permit a detailed assessment of primary homologies and taxonomically-relevant variation across the order. This provides the basis for a myological synonymy, which organizes 33 previously proposed names for 15 recognized muscles. Morphological variation derived from dorsolateral head musculature was coded into 56 characters. When analyzed in isolation, that set of characters results in Gymnotidae as the sister group of remaining gymnotiforms, and all other currently recognized families as monophyletic groups. In a second analysis, myological characters were concatenated with other previously proposed characters into a phenotypic matrix. Results of that analysis reveal new myological synapomorphies for nearly all taxonomic categories within Gymnotiformes. A Partitioned Bremer Support (PBS) was used to asses the significance of comparative myology in elucidating phylogenetic relationships. PBS values show strongly non-uniform distributions on the tree, with positive scores skewed towards more inclusive taxa, and negative PBS values concentrated on less inclusive clades. Our results provide background for future studies on biomechanical constraints evolved in the early stages of gymnotiform evolution.

Morphology and phylogenetic significance of the pelvic articular region in elasmobranchs (Chondrichthyes)

“…Negative PBS values (PBS−) for a node indicate that data partitions support relationships not corroborated in the global analyses, while positive PBS values (PBS+) mean complete congruence with that topology (Lambkin, 2004; Peña et al., 2006). Partitioned Bremer support was performed (Baker and DeSalle, 1997; Lambkin et al., 2002; Lambkin, 2004; Peixoto and de Pinna, 2022) using the “pbsup.run” script available for TNT (Peña et al., 2006), to estimate the relevance of the pelvic characters (Appendix S6).…”

Facial and opercular muscles in the Anguilliformes (Elopomorpha: Teleostei): Comparative anatomy and phylogenetic implications for the basal position of Protanguilla

“…Previous studies have relied on a relatively limited comparative framework of three to eight families (Eagderi, 2010; G. J. Nelson, 1967; Springer & Johnson, 2004, 2015). Facial and opercular muscles have proved highly informative in anatomical descriptions of several subgroups of bony fish, such as Notacanthiformes (Greenwood, 1977), Teleostei (Datovo & Vari, 2014; Winterbottom, 1974a), Tetraodontiformes (Winterbottom, 1974b), Stromateiformes (Pastana et al, 2021), Gymnotiformes (Peixoto & de Pinna, 2022), and Actinopterygii (Datovo and Rizzato, 2018). There is every reason to believe that similarly, valuable information awaits discovery in these myological complexes of anguilliforms.…”