Omalodontidae Ginter, Liao, and Valenzuela-Ríos, 2008

Potvin-Leduc, Daniel, Cloutier, Richard, Landing, Ed, Hernick, Linda Vanaller & Mannolini, Frank, 2015, Givetian (Middle Devonian) sharks from Cairo, New York (USA): Evidence of early cosmopolitanism, Acta Palaeontologica Polonica 60 (1), pp. 183-200 : 186

Family Omalodontidae Ginter, Liao, and Valenzuela-Ríos, 2008

Remarks.—The order Omalodontiformes is characterized by a tooth base that either extends labially or labio-basally or a relatively symmetrical base without a labial or lingual extension ( Ivanov et al. 2011) and is subdivided into two families, Aztecodontidae and Omalodontidae . The Aztecodontidae is characterized by a subrectangular root situated directly under the crown and includes Aztecodus / Anaerodus (probably synonymous; Ginter et al. 2010) and Manberodus ( Ginter et al. 2008, 2010). The Omalodontidae is characterized by a tooth base with a labially directed lobe ( Ginter et al. 2008, 2010) and includes Doliodus , Omalodus , and Portalodus ( Ginter et al. 2008) . The Omalodontiformes also includes a genus of uncertain affiliation, Siberiodus ( Ivanov and Rodina 2004) . The teeth of Karksiodus from the Givetian of Estonia ( Ivanov et al. 2011) also present a labially directed base but have not yet been affiliated to any order.

Although a base not lingually directed is a rare character among chondrichthyans, using it as a common denominator to unite the taxa has been questioned on the basis of differences in external and internal morphology ( Ivanov et al. 2011). For example, the histology of Omalodus is extremely similar to the histology of Phoebodus ( Hampe et al. 2004) and it has also been suggested that Omalodus could represent elements associated with the dermal skeleton of Phoebodus fastigatus rather than its teeth ( Ginter et al. 2010). In Karksiodus , while the base is labially directed, the structure of the crown is more comparable to the structure of the crown in antarctilamnids ( Ivanov et al. 2011). The scales that we tentatively attribute to Portalodus in the present paper are different from the ctenacanth-type scales of the geologically older Doliodus problematicus . The scales of D. problematicus , as well as other morphological characters, are closer to what is observed in antarctilamnids ( Miller et al. 2003; Gess 2011). Obviously, more material, and hopefully articulated, will be needed in order to establish with certainty the phylogenetic relationships of these sharks.