Abstract
The infraclass Teleostei is a highly diversified group of bony fishes that encompasses 96% of all species of living fishes and almost half of extant vertebrates. Evolution of various morphological complexes in teleosts, particularly those involving soft anatomy, remains poorly understood. Notable among these problematic complexes is the adductor mandibulae, the muscle that provides the primary force for jaw adduction and mouth closure and whose architecture varies from a simple arrangement of two segments to an intricate complex of up to ten discrete subdivisions. The present study analyzed multiple morphological attributes of the adductor mandibulae in representatives of 53 of the 55 extant teleostean orders, as well as significant information from the literature in order to elucidate the homologies of the main subdivisions of this muscle. The traditional alphanumeric terminology applied to the four main divisions of the adductor mandibulae – A1, A2, A3, and Aω – patently fails to reflect homologous components of that muscle across the expanse of the Teleostei. Some features traditionally used as landmarks for identification of some divisions of the adductor mandibulae proved highly variable across the Teleostei; notably the insertion on the maxilla and the position of muscle components relative to the path of the ramus mandibularis trigeminus nerve. The evolutionary model of gain and loss of sections of the adductor mandibulae most commonly adopted under the alphanumeric system additionally proved ontogenetically incongruent and less parsimonious than a model of subdivision and coalescence of facial muscle sections. Results of the analysis demonstrate the impossibility of adapting the alphanumeric terminology so as to reflect homologous entities across the spectrum of teleosts. A new nomenclatural scheme is proposed in order to achieve congruence between homology and nomenclature of the adductor mandibulae components across the entire Teleostei.
Highlights
The infraclass Teleostei [1] is a speciose group of ray-finned fishes (Actinopterygii) encompassing more than 31,000 valid extant species with this total progressively increased by the annual description of hundreds of new species from both fresh and marine waters [2]
Universal descriptive guidelines for components of the adductor mandibulae that apply to all species of the morphologically and taxonomically diverse infraclass Teleostei are an unachievable goal
As is the case for virtually all morphological traits, an elucidation of the homologies of the components of the highly modified adductor mandibulae muscle can in many lineages be only achieved via comparisons with less derived but comparatively closely related taxa (e.g., [8,20,22,23])
Summary
The infraclass Teleostei [1] is a speciose group of ray-finned fishes (Actinopterygii) encompassing more than 31,000 valid extant species with this total progressively increased by the annual description of hundreds of new species from both fresh and marine waters [2]. Teleosts demonstrate a remarkable repertoire of morphological modifications in all body systems. These reflect their adaptations to life in most aquatic habitats from ocean depths to high mountain streams and the multiple alternative behavioral and reproductive strategies within this assemblage. Myriad researchers have engaged in anatomical explorations of teleosts over the centuries and contributed to our knowledge of the vast array of morphological adaptations within the group. Notwithstanding these endeavors, the evolution of many morphological complexes remains poorly understood across the infraclass. This limitation is pervasive in the case of soft anatomical systems, including the skeletal musculature
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