It is only known with certainty from a single specimen, the rather abraded proximal part of a left tarsometatarsus which was found at Carmanah Point on Vancouver Island (Canada), where the Juan de Fuca Strait opens into the Pacific.

The deposits from which it originated were initially dated to the Eocene; subsequent authors have usually assigned them to the Early Miocene though certainly rocks from around the Eo-Oligocene boundary also occur in the region where it was found.

But the slightly older (Late Oligocene) Cladornis from the Argentinian part of Patagonia is known from a distal right tarsometatarsus only, and thus not directly comparable to Cyphornis.

[5] To set it apart from its alleged relatives, Cyphornis was early on separated in a family Cyphornithidae together with Palaeochenoides mioceanus and eventually also Tympanonesiotes wetmorei which are also little-known pseudotooth birds but inhabited the Atlantic.

Only if the Pacific lineage is sufficiently distinct, the Cyphornithidae would remain valid, but in this case they would presumably not include the Atlantic forms.