Chondrichthyes - Helodontiformes
Parent taxon: Holocephali according to J. A. Long 2011
See also Nelson 2006 and Nelson et al. 2016
Sister taxa: Chimaeri, Debeeriformes, Debeeriiformes, Delphyodontos, Edaphodus, Eugeneodontiformes, Holocephalomorpha, Iniopterygiformes, Macrodontacanthus, Menaspacanthus, Orodontiformes, Paraselachiamorpha, Paraselachimorpha, Petalodontiformes, Thoralodus, Trachyacanthi, Pseudodontichthyidae, Desmiodus, Euglossodus, Gregoriidae, Mesolophodus, Ageleodus, Cynopodius, Metaxyacanthus, Lagarodontidae, Brachyrhizodus
Subtaxa: Helodontidae
Ecology: nektobenthic carnivore
Distribution:
• Permian of Australia (1 collection), Greenland (1), Lithuania (1), United States (11: Oklahoma, Wyoming)
• Carboniferous of Canada (1: Alberta), Ukraine (1), the United Kingdom (7), United States (4: Arizona, Illinois, Indiana, Nebraska)
• Devonian of Australia (1)
Total: 28 collections including 33 occurrences