Scale structure of putative chondrichthyan Gladbachus adentatus Heidtke & Krätschmer, 2001 from the Middle Devonian Rheinisches Schiefergebirge, Germany

Abstract

Gladbachus adentatus is a putative chondrichthyan, known only from the holotype specimen, which comprises an articulated endoskeleton complete from head to pelvic region with the squamation also preserved. The scales superficially resemble those of placoderms more than sharks, in having a similar gross morphology, lamellar cellular bone forming the base and upright dentinous tubercles comprising the crown. The odontocytic mesodentine in the tubercles is comparable to that in the Osteostraci and in some acanthodian taxa, known only from isolated scales, and is probably the plesiomorphic form of dentine for Gnathostomata.

Keywords:

• chondrichthyes
• scale histology
• stem gnathostome
• Bergisch Gladbach
• Givetian
• ichthyolith

Acknowledgements

CJB acknowledges support of ARC Discovery Grants in 2002–2004 (when this study started) and 2010–2013, and provision of facilities by the University of Queensland during the initial work; both authors acknowledge the support of the Queensland Museum for provision of basic facilities. They thank Ulrich Heidtke for passing the scales to us for study, and Rein van der Camp for translation of the original German description of Gladbachus (April 2003). Helpful comments from two anonymous reviewers were much appreciated. This is a contribution to IGCP Project 596: Climate change and biodiversity patterns in the mid-Palaeozoic.