Journal Article

Angular cartilage structure and variation in Neotropical freshwater stingrays (Chondrichthyes: Myliobatiformes: Potamotrygonidae), with comments on their function and evolution

João Pedro Fontenelle, Thiago S Loboda, Matthew Kolmann and Marcelo R de Carvalho

in Zoological Journal of the Linnean Society

Published on behalf of The Linnean Society of London

Volume 183, issue 1, pages 121-142
Published in print May 2018 | ISSN: 0024-4082
Published online October 2017 | e-ISSN: 1096-3642 | DOI: https://dx.doi.org/10.1093/zoolinnean/zlx054
Angular cartilage structure and variation in Neotropical freshwater stingrays (Chondrichthyes: Myliobatiformes: Potamotrygonidae), with comments on their function and evolution

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Abstract

The various configurations of the jaws, anterior branchial arches and neurocranium provide some of the fundamental synapomorphies, distinguishing the major lineages of sharks, rays and ratfishes. For the Neotropical freshwater stingrays (family Potamotrygonidae), putatively unique skeletal elements, the angular cartilages, are intermediate between the hyomandibula and the lower jaw. These skeletal elements have been proposed as a synapomorphy for the potamotrygonids, but confidence in this character has been limited by poor sampling and taxonomic uncertainty, particularly regarding their ontogeny and homology. The morphology of the angular cartilages across the family is described, and the nomenclature of these structures is standardized. In addition, developmental and functional hypotheses for the origins of the angular cartilages are proposed. These cartilages, formed within the hyomandibular–Meckelian ligament, are suggested to be fibrocartilaginous in origin and aid in jaw kinesis. The angular cartilages are corroborated as a synapomorphy for Potamotrygonidae, although there is great variation within the family and similar structures have arisen independently in other extinct and extant batoid lineages. In potamotrygonines, the angular cartilages appear to have been lost in piscivorous Heliotrygon and Paratrygon, while additional angular cartilages were gained, typically one at a time, in some lineages of Potamotrygon.

Keywords: fibrocartilage; hyomandibulae; hyomandibular; Meckelian ligament; jaws; jaw suspension

Journal Article.  14035 words.  Illustrated.

Subjects: Evolutionary Biology ; Natural History ; Zoology and Animal Sciences

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