Helicoprionidae

Helicoprionidae Temporal range: 360–251 Ma PreЄ Є O S D C P T J K Pg N Early Carboniferous to Early Triassic
Helicoprion bessonovi
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Order:	†Eugeneodontida
Clade:	†Edestoidea
Family:	†Helicoprionidae Karpinsky, 1911
Type genus
Agassizodus St John and Worthen, 1875
Type species
Lophodus variabillis Newberry and Worthen 1870
Genera
Agassizodus Arpagodus Campyloprion Helicoprion Hunanohelicoprion Parahelicoprion Sarcoprion Shaktauites Sinohelicoprion Toxoprion
Synonyms
Agassizodontidae Zangerl, 1981

The Helicoprionidae are an extinct, poorly known family of bizarre holocephalids within the poorly understood order Eugeneodontida. Members of the Helicoprionidae possessed a unique "tooth-whorl" on the symphysis of the lower jaw and pectoral fins supported by long radials. The closest living relatives of the Helicoprionidae and all other eugeneodontids are the ratfishes. The anatomy of the tooth-whorl differed amongst genus and species, some possessing complete spirals (such as those of Helicoprion), others possessing halved spirals (seen in Parahelicoprion), and some with wedged half-spirals (seen in Sarcoprion). Each tooth-whorl is thought to be adapted to a different type of prey, and a different predation strategy.