Helicoprionidae

Helicoprionidae (sometimes referred to as Agassizodontidae)^[2] is an extinct family of holocephalans within the order Eugeneodontida. Members of the Helicoprionidae possessed a "whorl" of tooth crowns connected by a single root along the midline of the lower jaw.^[2][3] While historically considered elasmobranchs related sharks and rays,^[2] the closest living relatives of the Helicoprionidae and all other eugeneodonts are now thought to be the ratfishes.^[4] The anatomy of the tooth-whorls vary between taxa, with some possessing highly specialized, coiling spirals (such as those of the namesake genus Helicoprion), while others such as Sarcoprion and Parahelicoprion possessed shorter whorls.^[2]

Helicoprionidae Temporal range: 358–252 Ma PreꞒ Ꞓ O S D C P T J K Pg N Early Carboniferous to Late Permian
Helicoprion
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Holocephali
Order:	†Eugeneodontida
Clade:	†Edestoidea
Family:	†Helicoprionidae Karpinsky, 1911
Type genus
Helicoprion Karpinsky, 1899[1]
Type species
Helicoprion bessonowi Karpinsky, 1899
Genera
Agassizodus Arpagodus Campyloprion Helicoprion Hunanohelicoprion Karpinskiprion Parahelicoprion Sarcoprion Shaktauites Sinohelicoprion Toxoprion
Synonyms
Agassizodontidae Zangerl, 1981[1]