![]() However, with successive discoveries of new taxa preserved in greater detail, Cladoselache is increasingly marginalized in spite of its exceptional soft-tissue preservation and completeness (Dean, 1909a, 1909b). However, alternative hypotheses remain current, and these posit Symmoriiformes as either stem chondrichthyans (Denton & Goolsby, 2021) or stem elasmobranchs (Hodnett et al., 2021).Ĭladoselache, the classic primitive shark of older textbooks (e.g., Romer 1966) and occasional model for a gnathostome archetype (Jarvik 1980), is now most commonly associated with the symmoriiform grade or clade (e.g., Coates et al., 2017 Maisey, 2007). Among the stem holocephalans, the Symmoriiformes are an important group, comprising a series of bizarre species, several of which bear unusual fin spines (Coates & Sequeira, 1998, 2001 Lund, 1985, 1986 Williams, 1985 Zangerl, 1990 Zangerl & Case, 1976). 2022 Coates et al., 2018), and thus all crown gnathostomes, originated at least as far back as the early Silurian (Andreev et al., 2022 Zhu et al., 2022). With this change has come increasing recognition that total group Chondrichthyes (Andreev et al. Emerging consensuses include the wholesale movement of acanthodians on to the chondrichthyan stem (Brazeau, 2009 Davis et al., 2012 Dearden et al., 2019 Maisey et al., 2017 Miller et al., 2003 Zhu et al., 2013), and, more contentiously, recognition of numerous Paleozoic clades as stem holocephalans (Coates et al., 2017, 2018 Dearden et al., 2019 Frey et al., 2020a, b). Our understanding of chondrichthyan phylogeny has been vastly improved in recent years by the addition of anatomical information from three-dimensional crania (including endocasts) and enriched sampling of postcrania (Coates & Sequeira, 2001 Coates et al., 2017 Davis et al., 2012 Frey et al., 2020a, b Pradel et al., 2009, 2011). This suggests sensory specialization approaching that of extant broad-rostrum elasmobranchs and represents a significant addition to increasingly apparent ecomorphological diversity among early chondrichthyans. Remarkably, this new stem holocephalan is equipped with a wide snout and large laterally separated nasal capsules: the earliest known example of this condition in the chondrichthyan and (perhaps) gnathostome record. Further phylogenetic results corroborate that the initial evolutionary radiation of crown chondrichthyans occurred within or before the Late Devonian. ![]() Phylogenetic analyses place the family Cladoselachidae as the sister group of symmoriiforms and these groups as sister group of the holocephalans. ![]() Key details of the dentition, jaws, and pectoral skeleton are shared with the iconic genus Cladoselache. from the eastern Anti-Atlas of Morocco is known from multiple specimens preserving most of its skeletal features, which in some instances are preserved in three dimensions. The Late Devonian shark taxon Maghriboselache mohamezanei gen. Throughout the Silurian and Devonian, cartilaginous fish successively evolved their specialized skeletal and dental characteristics, and increasingly refined their sensory systems. ![]()
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