The functional morphology of the pectoral fin girdle of the Spiny Dogfish (Squalus acanthias): Implications for the evolutionary history of the pectoral girdle of vertebrates

Abstract

Fresh functional-morphological observations and theoretical considerations warrant a re-analysis of the traditional assumptions that the head skeleton of sharks consists of the chondrocranium and visceral arches and that the pectoral fin girdle is part of the appendicular skeleton. The scapulocoracoid cartilage of the Spiny Dogfish (Squalus acanthias) plays at least three major roles: (1) Asa mechanical separator between the lateral undulations of the trunk and the vertical movements of the visceral arches; (2) asa structural basis for the anchoring of the pectoral fins: and (3) as the place of origin of the cucullaris and hypobranchial muscles which not only open the jaws and expand the branchial basket, but at the same time also affect the contractions of the heart and the timing of blood flow through the gills. Hence, the scapulocoracoid cartilage is an integral part of the head. It most likely evolve d in connection with the evolution of the jaw apparatus and not simply as a part of the appendicular skeleton. Furthermore, the head is a mechanically coherent system, in which the central alimentary, circulatory, respiratory and nervous systems of the organism converge. These central feeding, respiratory and circulatory functions are not simply choreographed by the central nervous system, but are concatenated by the mechanical construction of the head itself. Sueh a conceptualization of the selachian head raises fresh questions concerning the constraints and potentialities of the evolutionary transformations of the various components of the head and pectoral appendages during the transition from aquatic pisciform to terrestrial tetrapod vertebrates.

A new scenario of the evolutionary derivation of the mammalian diaphragm from shoulder muscles

“…On the other hand, the hypobranchial and pectoral muscles in non‐tetrapod gnathostomes (that is, fishes) are contiguous, surrounding the pericardium in both adult anatomy (Marinelli & Strenger, , ; Gudo & Homberger, ) and embryonic development (Greil, , ; Edgeworth, , ). Tanaka et al () recognized an integration of the hypobranchial and pectoral muscle systems as the ‘hypobranchio‐pleuropericardiaco‐pectobrachial region’, and considered that the diaphragm evolved in this region, taking into consideration the human variation of communications between the phrenic nerve and the cervical ansa.…”

A NEW RECONSTRUCTION OFONYCHOSELACHE TRAQUAIRI, COMMENTS ON EARLY CHONDRICHTHYAN PECTORAL GIRDLES AND HYBODONTIFORM PHYLOGENY

“…5). The variety of girdle shapes reflects their various functional roles: as pectoral fin supports, as mechanical separators between trunk and visceral arch musculo‐skeletal systems, and as origination sites for cucullaris and hypobranchial muscles (Gudo and Homberger 2002). Given this mixture of biomechanical demands, it is likely that clade‐specific morphologies are present, and that these reflect phylogenetic pattern.…”

Anatomy and early development of the pectoral girdle, fin, and fin spine of sturgeons (Actinopterygii: Acipenseridae)

“…The pectoral girdle is situated at the division between the head and trunk regions, and is used in different functions specific to each region (Gudo and Homberger, 2002). As in all fishes, the pectoral girdle of sturgeon serves as the origin for muscles associated with feeding (Carroll and Wainwright, 2003), is a powerful structure used for movement (Liem et al, 2001, McGonnell, 2001, and station holding (Wilga andLauder, 1999, Kane andHigham, 2012); see Drucker and Lauder (2002) for a review of the evolution of pectoral girdle function in actinopterygians, specifically with regard to its role in locomotion.…”