''Thrinacodus'' is an extinct genus of basal

elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks ( division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by h ...

, found worldwide from the Late Devonian-Lower Carboniferous. The type species is ''Thrinacodus nanus''. Most species are only known from their tricuspid teeth. ''T. gracia'', originally placed in the separate genus ''Thrinacoselache'' from the

Serpukhovian The Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from Ma to Ma. It is preceded by the Visean and is followed ...

-aged

Bear Gulch Limestone The Bear Gulch Limestone is a limestone-rich Lens (geology), geological lens in central Montana, renowned for the quality of its marine fossils from the late Mississippian (geology), Mississippian subperiod, about 324 million years ago. It is expo ...

, of what is now

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

, is known from full body impressions, showing a long, slender eel-like body up to a metre in length, with an elongate rostrum. Stomach contents of ''T. gracia'' include remains of crustaceans and small

chondrichthyan Chondrichthyes (; ) is a class (biology), class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which ...

fish (''

Harpagofututor ''Harpagofututor'' is an extinct genus of eel-like cartilaginous fish from the Early Carboniferous ( Mississippian). It is primarily known from complete specimens discovered in the Bear Gulch Limestone of Montana, as well as an isolated tooth fr ...

'' and ''

Falcatus ''Falcatus'' is an extinct genus of falcatid chondrichthyan which lived during the early Carboniferous Period in Bear Gulch bay in what is now Montana. Description This fish was quite small, only getting to around 25–30 cm or 10-12 i ...

''). It is a member of the Phoebodontiformes.

References

Phoebodontiformes Carboniferous cartilaginous fish Fossil taxa described in 1875 Carboniferous fish of North America {{paleo-cartilaginous-fish-stub