The dentition of Omalodontiformes, the order of unusual Devonian stem-chondrichthyans

Abstract

The early chondrichthyan order Omalodontiformes from the late Early Devonian through to the Late Devonian is characterised by specific teeth. Unlike in most Devonian sharks, their bases are directed labially or are reduced and devoid of labial or lingual extensions. In this paper the complex history of investigation on the dermal skeleton of omalodontiforms is presented and the validity of the established taxa is revised. The dentition of an Emsian representative of this group, known from a single articulated specimen (NMBG 10127) and several isolated fin spines from Canada and previously, probably incorrectly, attributed to Doliodus, is distinctly heterodont. The nature of this heterodonty suggests that the two omalodontiform tooth-based genera described originally from the Middle/Upper Devonian Aztec Siltstone (Antarctica), viz. Portalodus and Anareodus, are in fact congeneric as their teeth represent different parts of the same jaw. Because the teeth of the Canadian specimen differ in important aspects from those of typical Doliodus and are generally similar to those of Portalodus, it probably should be placed in a new genus. Also, the validity of the distinction between Portalodus bradshawae and P. mannoliniae is considered questionable.