Its remains were found in the Ypresian (Early Eocene) London Clay of the Isle of Sheppey (England), where they were deposited about 50 Ma (million years ago) in the Mammal Paleogene zone MP8-9.

Due to the scarcity of their fossil remains, is not clear whether the pseudotooth bird species described as Pseudodontornis longidentata is not the same as M. oweni, though its size suggests that it is more likely to be synonymous with D. emuinus.

[3] If Macrodontopteryx is indeed a distinct genus, perhaps some pseudotooth bird fossils found in Lutetian (Middle Eocene, MP11-13, about 45 Ma) deposits at Etterbeek (Belgium) belong therein.

Like the holotype BMNH A1, they have been assigned to Argillornis longipennis in the past; at least some of the material[4] placed in that taxon at one time or another – but not its syntype humerus pieces – seems too small to be of an adult Dasornis.

An equally old cervical vertebra fragment (specimen BMNH A-4413) and a toe phalanx from nearby Yarmouth were, mainly due to their size, believed to be related to the enigmatic large flightless bird (and presumed ratite) Eleutherornis.