Wikipedia
Diogenornis fragilis is an extinct ratite that lived during the Paleocene. It was described in 1983 by Brazilian scientist Herculano Marcos Ferraz de Alvarenga. The type species is D. fragilis. While initially considered a member of the family Opisthodactylidae, further examination of the fossil remains showed that it was more similar to the modern Rhea. According to Gerald Mayr, Diogenornis is best considered a stem-group member of the Rheidae. It grew to about two thirds the size of the modern greater rhea, at about 90 centimeters of height.
However, recent phylogenetic studies have shown a closer affiliation to Australian ratites, the cassowaries and emus. This may reevaluate the origins and distribution of this clade, expanding their range to the South American Paleocene, well before the appearance of Emuarius.
Diogenornis possesses a rather narrow beak, similar to that of tinamous, lithornithids and cassowaries, as well as rather large wings. These traits, both rather unspecialised, seem to suggest a then recent development from a flying ancestor.