Role of Paedomorphosis in the Emergence of the Skull Bauplan in Acipenseriformes (Actinopterygii)
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of Paedomorphosis in the Emergence of the Skull Bauplan in Acipenseriformes (Actinopterygii) A. A. Tsessarsky* Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow, 119071 Russia *e-mail: [email protected] Received August 7, 2018; revised January 27, 2019; accepted June 6, 2019
Abstract—Acipenseriformes (Actinopterygii) are commonly recognized as a sister group of Neopterygii. They represent the basal-most taxa of extant ray-finned fishes, along with Polypterus (Polypteriformes). This position on the cladogram determines the key importance of sturgeons for an understanding of the evolutionary history of actinopterygians, as well as bony fishes in general. However, their unique morphology and the absence of any reliable homologies (in particular, for the snout region and jaw arch) make these fishes ineffective for the testing of phylogenetic hypotheses and the reconstruction of the evolution of Osteichthyes. This article presents the results of a comparative anatomical analysis of the jaw arch and snout region in sturgeons. The homologies of these parts are established, and an evolutionary scenario is proposed to explain the transformation of the mandibular arch and snout region during the presumed transition from palaeoniscoid ancestors to Acipenseriformes. It is shown that these transformations were triggered by paedomorphosis, which caused, inter alia, underdevelopment of the lower jaw. This underdevelopment resulted in a release of the anterior ends of the upper jaw rami and the entire snout region from restrictions concerning the functioning of the jaw apparatus. DOI: 10.1134/S2079086420050084
INTRODUCTION Sturgeons (Acipenseridae: Acipenser, Huso, Scaphirhynchus, and Pseudoscaphirhynchus) and polyodontids (Polyodontidae: Psephurus and Polyodon), together with two fossil families (Chondrosteidae and Peipiaosteidae), form a crown group, Acipenseriformes, that is commonly ranked as an order (Bemis et al., 1997). The current cladograms consider Acipenseriformes to be a sister group of Neopterygii (Amia and Lepisosteus and Teleostei) that represents the basal-most taxa of extant ray-finned fishes, along with Polypterus (Grande and Bemis, 1996; Cloutier and Abbreviations: Aup, pars autopalatina, Br.m.1, basirostrale mediale 1, Br.m.2, basirostrale mediale 2, C.tent., cartilage tentacularis, CM, cartilage Meckelii, Cr.add., crista adductories, Cr.Br., crista basirostrale, Dep.add., deppressio adductories, Dpl, dermopalatinum, Ect, ectoptrygoideum, Ent, entoptrygoideum, F.bpt., foramen basipterygoideus, Hm, hyomandibulare, HmSy, hyosymplecticum, Io, infraorbitale, Lab.s., labrum superius, Lig.bas., ligamentum basalis, Lig.ep., ligamentum ethmopalatinus, M.add., musculus adductor mandibulae, Mx, maxillare, Pl.ppt., plica postpterygoideum, Pl.smx., plica supramaxillaris, Po, postorbitale, Pop, praeoperculum, Ppt, postpterygoideum, Pq, palatoquadratum, Pmx, premaxillare, Proc.bpt., processus basipterygoideus, Proc.pb.m., processus palatobasalis medialis, Prsp, parasphenoideum, Qj, quadrato
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