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| Protospinax annectans Woodward, 1918 in Jambura, Villalobos-Segura, Türtscher, Begat, ... et Kriwet, 2023. DOI: 10.3390/d15030311 |
Abstract
The Late Jurassic elasmobranch Protospinax annectans is often regarded as a key species to our understanding of crown group elasmobranch interrelationships and the evolutionary history of this group. However, since its first description more than 100 years ago, its phylogenetic position within the Elasmobranchii (sharks and rays) has proven controversial, and a closer relationship between Protospinax and each of the posited superorders (Batomorphii, Squalomorphii, and Galeomorphii) has been proposed over the time. Here we revise this controversial taxon based on new holomorphic specimens from the Late Jurassic Konservat-Lagerstätte of the Solnhofen Archipelago in Bavaria (Germany) and review its skeletal morphology, systematics, and phylogenetic interrelationships. A data matrix with 224 morphological characters was compiled and analyzed under a molecular backbone constraint. Our results indicate a close relationship between Protospinax, angel sharks (Squatiniformes), and saw sharks (Pristiophoriformes). However, the revision of our morphological data matrix within a molecular framework highlights the lack of morphological characters defining certain groups, especially sharks of the order Squaliformes, hampering the phylogenetic resolution of Protospinax annectans with certainty. Furthermore, the monophyly of modern sharks retrieved by molecular studies is only weakly supported by morphological data, stressing the need for more characters to align morphological and molecular studies in the future.
Keywords: phylogenetics; elasmobranch evolution; calibration fossil; molecular backbone constraint; hypnosqualea; Mesozoic; Solnhofen Archipelago; Konservat-Lagerstätte
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| New fossil skeletal material of Protospinax annectans Woodward, 1918 examined in this study. (A) PBP-SOL-8007; (B) MB 14-12-22-1; (C) UMN uncatalogued; (D) JME-SOS 3386; (E,F) FSM 727. Abbreviations: bp, basal plate; dfs, dorsal fin spine; sne, supraneuralia; vc, vertebral column. |
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| Environmental reconstruction of the Tithonian (Late Jurassic) Solnhofen Archipelago, showing Protospinax annectans in association with the Late Jurassic ray Asterodermus platypterus. |
Patrick L. Jambura, Eduardo Villalobos-Segura, Julia Türtscher, Arnaud Begat, Manuel Andreas Staggl, Sebastian Stumpf, René Kindlimann, Stefanie Klug, Frederic Lacombat, Burkhard Pohl, John G. Maisey, Gavin J. P. Naylor and Jürgen Kriwet. 2023. Systematics and Phylogenetic Interrelationships of the Enigmatic Late Jurassic Shark Protospinax annectans Woodward, 1918 with Comments on the Shark–Ray Sister Group Relationship. Diversity. 15(3); 311. DOI: 10.3390/d15030311
(the Special Issue: Evolution and Diversity of Fishes in Deep Time)
