Elopteryx is a genus of paravian theropod dinosaur based on fragmentary fossils found in Late Cretaceous rocks of Romania.

[1][2] In the late nineteenth or early twentieth century, the famous Hungarian paleontologist Franz Nopcsa von Felső-Szilvás found near Sînpetru, in what is now the Romanian region of Transylvania, some bone fragments of a small theropod.

A distal left tibiotarsus was also tentatively assigned to this taxon; it was initially classified with the same specimen number as the holotype and was found in close proximity, but may not be from the same individual (see below).

The fossils date from the early-late Maastrichtian (Begudian) faunal stage, circa 70-66 million years ago, originating from the Sânpetru Formation of the Hațeg Island.

[6] The supposed family Elopterygidae was initially placed in the suborder Sulae – then still in the polyphyletic "Pelecaniformes" – in 1963 by Pierce Brodkorb in his fossil bird catalogue, and the Cenozoic genera Argillornis and Eostega were moved to it.

[3] In 1978 Brodkorb had changed his opinion after the supposed Elopteryx material was divided among three species in total, and was actually the first scholar in modern times to suggest that these Mesozoic bones were not of birds but of non-avian dinosaurs.

that Bradycneme and Heptasteornis should be synonymized with E. nopcsai again, and a femur (MDE-D203), an anterior dorsal vertebra (MDE-D01), a posterior sacral vertebra (MDE collection, unnumbered) and some dorsal rib fragments from the Jurassic Grès à Reptiles formation of France were described as an indeterminate species of Elopteryx; that study placed all this material in the Dromaeosauridae or a family or subfamily (Elopteryginae) very close to these.

[13] The French femur is similar in general appearance to the Elopteryx type but it differs in diagnostic traits, e.g. lacking a fourth trochanter.

In 2004, Darren Naish and Gareth Dyke considered Elopteryx as a Eumaniraptora incertae sedis, possibly either a non-ornithuromorphan pygostylian bird[18] or a troodontid, while Bradycneme would be a maniraptoran, and the dubious Heptasteornis (at least its holotype BMNH A4359) a member of the Alvarezsauridae.