A NEW RECONSTRUCTION OFONYCHOSELACHE TRAQUAIRI, COMMENTS ON EARLY CHONDRICHTHYAN PECTORAL GIRDLES AND HYBODONTIFORM PHYLOGENY

Abstract

A new, third, specimen of Onychoselache traquairi from the Viséan (Holkerian) of Scotland allows a significant revision of the anatomy of this stem-group elasmobranch. This first report of material from the Mumbie Quarry exposure of the Glencartholm fish beds presents a new reconstruction of Onychoselache showing broad-based cephalic and nuchal spines, and exceptionally large pectoral fins. Details of the jaws, braincase and postcranial skeleton demonstrate that Onychoselache is a well-characterized member of the Hybodontiformes. Comparisons of the pectoral skeleton with other early chondrichthyan examples, including new material of Tristychius arcuatus and Plesioselachus macracanthus, highlight a range of early chondrichthyan conditions that are incorporated into a revised hybodontiform phylogeny. Close resemblance between Onychoselache and Mesozoic and late Palaeozoic hybodonts implies that these clades diverged within the Carboniferous and Permian. Major differences between Onychoselache and the coeval Tristychius (a modified reconstruction of which is included) indicate that the Neoselachii-Hybodontiformes split is probably Late Devonian, consistent with records of isolated teeth. The pectoral fins of Onychoselache, while unique among Palaeozoic forms, resemble those of Recent bamboo and epaulette sharks (Orectolobiformes). The functional corollary of this convergence is that Onychoselache represents an instance of a non-tetrapod early vertebrate with a nearwalking gait.

Pectoral fin of the Paleozoic shark,Cladoselache: new reconstruction based on a near-complete specimen

“…Posteriorly, it contacts the coracoid plate. Two procoracoids, located on each side of the pectoral girdle, are also found in many Paleozoic chondrichthyans (e.g., eugeneodontids, symmoriids, stethacanthids, and xenacanths), whereas this cartilage is absent in hybodonts and extant elasmobranchs (Zangerl, 1981;Coates and Gess, 2007). A paired procoracoid is also found in CMNH 5371 and has the same features as CMNH 8114.…”

“…Journal of Vertebrate Paleontology e973029 (4 pages) Ó by the Society of Vertebrate Paleontology DOI: 10.1080DOI: 10. /02724634.2015 2001a) but is distinguished from the rectangular coracoids of hybodonts (Onychoselache, Tribodus, and Lissodus) (Coates and Gess, 2007;Lane and Maisey, 2009).…”

The characters of Palaeozoic jawed vertebrates

“…In chondrichthyans, the scapulocoracoid bears a tall blade or process that forms the posterior boundary of the gill chamber and provides an origin for the neck muscles and anterior trunk muscles (Zangerl, 1981;Liem & Summers, 1999;Stahl, 1999;Gudo & Homberger, 2002;Coates & Gess, 2007;Anderson, 2008). A similar process is observed in a large number of acanthodians (Miles, 1973a;Denison, 1979), and is only absent in taxa in which the whole pectoral endoskeleton is unpreserved.…”

The oldest record of gnathostome fossils from Greece: Chondrichthyes from the Lopingian of Hydra Island

“…Our specimen differs from Hamiltonichthys in exhibiting more rounded corners at the mesial and distal end of the crown in occlusal view. Onychoselache (Coates and Gess, 2007) exhibits teeth of more subtle crown ornamentation and higher roots than AMPG 550. Finally, unicuspidate Lissodus teeth have strongly lingually bent roots, whereas mesiodistal and labiolingual occlusal crests form more pronounced, sharp, and often jagged, cutting edges (Rees and Underwood, 2002;Duncan, 2004;Ginter et al, 2010).…”

“…Despite the uncertain affinities of Acronemus within euselachians, its tooth morphology is hybodontiform-like (Rieppel, 1982;Maisey, 2011;Cappetta, 2012), and resemblant to that of AMPG 550. One of the most conspicuous differences among the abovementioned genera is the occurrence of a lingual crown protuberance in Hamiltonichthys (Maisey, 1989), Onychoselache (Coates and Gess, 2007) and Acronemus (Rieppel, 1982), rather than a labial one as in most other Hybodontiformes.…”