Chondrichthyes - Helodontiformes
Parent taxon: Holocephali according to R. van der Laan 2019
See also Long 2011, Nelson 2006 and Nelson et al. 2016
Sister taxa: Chimaeri, Debeeriformes, Debeeriiformes, Delphyodontos, Desmiodontidae, Desmiodus, Edaphodus, Eugeneodontiformes, Gregoriidae, Harpacanthidae, Holocephalomorpha, Iniopterygiformes, Lagarodontidae, Macrodontacanthus, Menaspacanthus, Orodontiformes, Paraselachiamorpha, Paraselachimorpha, Petalodontiformes, Thoralodus, Trachyacanthi, Euglossodus, Cynopodius, Mesolophodus, Metaxyacanthus, Ageleodus
Subtaxa: Helodontidae
Ecology: nektobenthic carnivore
Distribution:
• Permian of Australia (1 collection), Greenland (1), Lithuania (1), United States (12: Oklahoma, Texas, Wyoming)
• Carboniferous of Canada (1: Alberta), Ukraine (1), the United Kingdom (7), United States (4: Arizona, Illinois, Indiana, Nebraska)
• Devonian of Australia (1)
Total: 29 collections including 34 occurrences