Chondrichthyan-like scales from the Middle Ordovician of Australia

Abstract

Microvertebrate sampling of the Stairway Sandstone (Darriwilian, Middle Ordovician, central Australia) has yielded scales that are chondrichthyan-like in their overall construction, and Tantalepis gatehousei gen. et sp. nov. is erected here to describe these specimens. Tantalepis gatehousei gen. et sp. nov. is the stratigraphically oldest microsquamous taxon described thus far, and the 'shark-like' appearance of the scales may extend the chondrichthyan lineage back into the Middle Ordovician. The presence of 'shark-like' scales in the fossil record some 50myr prior to the first articulated chondrichthyan body fossils and 44myr before the first clearly identifiable chondrichthyan teeth suggests there is a considerable scope for the recovery of articulated specimens with which to document the early history of crown gnathostomes. Traditional hypotheses of phylogenetic relationships among early jawed vertebrates were recently challenged by the proposal of a radically different tree topology. However, the development of a new data set specifically addressing scale-based characters is required before taxa such as Tantalepis, that are based upon disarticulated remains alone, can be firmly placed within the emerging, revised, evolutionary narrative.