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

Abstract

The morphology of the articular region of the scapulocoracoid and the basal cartilages of the pectoral fin endoskeleton of elasmobranchs is reviewed in detail. Examination of this specific morphology in more than 140 species of elasmobranchs (of which 40 are reported here) revealed characters that may have a bearing on the higher-level phylogeny of the group. Ten distinct characters of the scapular articular region of elasmobranchs are described, varying in terms of the number of distinct articular sites as well as their specific morphology (e.g. whether the articular surface is composed of condyles and/or facets). Previous interpretations of the articular region in morphological phylogenies are also reviewed, revealing much more morphological variation than formerly reported. These prior characters played an important role in supporting the Hypnosqualea, and may still be derived for this clade. The variation and distribution of the new characters discussed provide new insights for the evolution of the pectoral endoskeleton in chondrichthyans. They also highlight the continued importance of morphological characters for phylogenetic studies, and reinforce the necessity of in-depth anatomical reviews of certain characters employed in previous higher-level phylogenetic studies of elasmobranchs.

Comparative anatomy of the extraocular muscles in four Myliobatoidei rays (Batoidea, Myliobatiformes)

“…In Myliobatiformes, the pectoral girdle has four distinct articular regions constituted by three condyles and a facet (Da Silva & De Carvalho, 2015) and a diverse general locomotor behavior (Rosenberger, 2001). Stingrays such as Dasyatis species have pectoral fin skeletal structures with reduced calcification and joint staggering (Schaefer & Summers, 2005); they move with an undulatory swimming mode (Rosenberger, 2001) and feed mainly on benthic prey (Jacobsen & Bennett, 2013).…”

A complete protocol for the preparation of chondrichthyan skeletal specimens

“…Maisey, , ; Pradel et al., , ) or extant species (e.g. Shirai, ; Aschliman, ; Silva and de Carvalho, ; Silva et al., ). Furthermore, the key position of chondrichthyans in the phylogeny of vertebrates makes them an invaluable group in evo‐devo studies, making it possible to infer the evolution of skeletal characters in the gnathostome tree (e.g.…”

The evolution of underwater flight: The redistribution of pectoral fin rays, in manta rays and their relatives (Myliobatidae)

“…Species from two families including the Myliobatidae (manta and devil rays, cownose rays, bat rays and eagle rays) and Gymnuridae (butterfly rays) have adopted a more pelagic lifestyle and utilize the oscillatory swimming mode. As such, they have several derived pectoral fin modifications, including lateral expansion of the pectoral fins resulting in an increased aspect ratio relative to the ancestral batoid body plan (Fontanella et al, 2013), anteroposterior elongation of the pectoral girdle (scapulocoracoid, Da Silva & De Carvalho, 2015;McEachran, Dunn, & Miyake, 1996;Nishida, 1990), and stiffening by crustal calcification of radials and cross-bracing among fin rays (Heine, 1992;Lighthill, 1969;Mulvany & Motta, 2013;Rosenberger, 2001;Schaefer & Summers, 2005). These derived morphologies are associated with oscillatory swimming, where the wing-like pectoral fins oscillate up and down in a flapping motion, analogous to flight in birds, and is characterized by having less than half a wavelength along the pectoral fin margin (Heine, 1992;Rosenberger, 2001;Webb, 1994).…”