Fadenia is an extinct genus of eugeneodontid holocephalian chondrichthyan from the Carboniferous Period of Missouri (United States), the Permian period of Greenland, and the Early Triassic epoch of British Columbia, Canada (Sulphur Mountain Formation).

[2][3] The first fossils of Fadenia were discovered and described in the periodical Meddelelser om Grønland in 1932 by the Danish vertebrate palaeontologist Eigil Nielsen after studying the Upper Permian beds of Cape Stosch, in the fjord of Godthab Gulf in King Christian X Land, East Greenland.

Nielsen had joined at the beginning of the Three-year Expedition to East Greenland led by Danish geologist and explorer Lauge Koch.

The manager of the expedition was the botanist Gunnar Seidenfaden, after whose surname the genus was named.

They include iconic genera, such as Helicoprion (buzz-saw shark), Ornithoprion, Edestus or Caseodus.