Non-tetrapod sarcopterygians from the Valentia Slate Formation (Givetian, Devonian) of the Iveragh Peninsula, south-western Ireland: systematic reappraisal and palaeobiogeographic implications

Abstract

The Middle Devonian (Givetian) Valentia Slate Formation in the Iveragh Peninsula, southwest Ireland, is more renowned for the second oldest record of tetrapod trackways in the world than for its heavily metamorphosed bone remains. The present study focuses on new discoveries of non-tetrapod sarcopterygian fish fossils from the Valentia Slate Formation. Micro-CT scanning technology allows a re-interpretation of a previously published acanthodian fin spine as a fanged coronoid of a probable Rhizodontida and the identification of a Dipnoi tooth plate and bone. In addition, a scale of Holoptychius is described. The presence the rhizodont suggests Gondwanan ties and a first northward dispersal wave of these vertebrates into Euramerica as early as middle Givetian. This hypothesis is supported by the common occurrence of the placoderm Bothriolepis in the Valentia Slate Formation.