''Diogenornis'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of ratites, that lived during the Early Eocene (

Itaboraian The Itaboraian ( pt, Itaboraiense) age is a period within the Early Eocene geologic time (53.0–50.0 Ma) epoch of the Paleogene, used more specifically with South American land mammal ages (SALMA). It follows the Riochican and precedes the Cas ...

Casamayoran The Casamayoran ( es, Casamayorense) age is a period of geologic time (50.0–48.0 Ma) within the Early Eocene epoch of the Paleogene, used more specifically within the South American land mammal age (SALMA) classification. It follows the Itaboraia ...

in the SALMA classification).''Diogenornis''
at Fossilworks.org It was described in 1983 by Brazilian scientist Herculano Marcos Ferraz de Alvarenga based on fossils found in the

Itaboraí Formation The Itaboraí Formation ( pt, Formação Itaboraí) is a highly fossiliferous geologic formation and LagerstätteKellner & Campos, 1999, p.399 of the Itaboraí Basin in Rio de Janeiro, southeastern Brazil. The formation reaching a thickness of i ...

in southeastern

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

.Alvarenga, H.M.F. (1983) Uma ave ratitae do Paleoceno Brasileiro: bacia calcária de Itaboraí, Estado do Rio de Janeiro, Brasil. ''Boletim do Museu Nacional, Nova Série, Geologia'' 41: 1–8 The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

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 Gerald Mayr is a German palaeontologist who is Curator of Ornithology at the Senckenberg Research Institute in Frankfurt am Main, Hesse. He has published extensively on fossil birds, especially the Paleogene avifauna of Europe. He is an expert on ...

, ''Diogenornis'' is best considered a stem-group member of the

Rheidae Rheidae is a family of flightless ratite birds which first appeared in the Paleocene. It is today represented by the sole living genus '' Rhea'', but also contains several extinct genera. Taxonomy Order Rheiformes (Forbes, 1884) Furbringer, 18 ...

.Mayr, G. (2009). Paleogene fossil birds. Springer. It grew to about two thirds the size of the modern

greater rhea The greater rhea (''Rhea americana'') is a species of flightless bird native to eastern South America. Other names for the greater rhea include the grey, common, or American rhea; ema (Portuguese); or ñandú (Guaraní and Spanish). One of two sp ...

, at about of height.

Description

However, recent phylogenetic studies have shown a closer affiliation to Australian ratites, the cassowaries and

emu The emu () (''Dromaius novaehollandiae'') is the second-tallest living bird after its ratite relative the ostrich. It is endemic to Australia where it is the largest native bird and the only extant member of the genus '' Dromaius''. The emu ...

s. This may reevaluate the origins and distribution of this clade, expanding their range to the South American Paleocene, well before the appearance of ''

Emuarius ''Emuarius'' is an extinct genus of casuariiform flightless bird from Australia that lived during the early Miocene and late Oligocene. It is one of two known genera of emu. There are two known species in the genus, ''Emuarius gidju'' and ' ...

''.H. Alvarenga, Diogenornis fragilis Alvarenga, 1985, restudied: a South American ratite closely related to Casuariidae, 2010 Recent findings nonetheless show that it co-existed with early rheas, meaning the ratite diversity of South America was very high during the Paleogene.Agnolin et al, "Unexpected diversity of ratites (Aves, Palaeognathae) in the early Cenozoic of South America: palaeobiogeographical implications Article in Alcheringa" ''An Australasian Journal of Palaeontology'' July 2016 DOI: 10.1080/03115518.2016.1184898 ''Diogenornis'' possesses a rather narrow beak, similar to that of

tinamous Tinamous () form an order of birds called Tinamiformes (), comprising a single family called Tinamidae (), divided into two distinct subfamilies, containing 46 species found in Mexico, Central America, and South America. The word "tinamou" comes ...

lithornithids Lithornithidae is an extinct, possibly paraphyletic (but see below) group of early paleognath birds. They are known from fossils dating to the Upper Paleocene through the Middle Eocene of North America and Europe, with possible Late Cretaceous r ...

and cassowaries, as well as rather large wings. These traits, both rather unspecialised, seem to suggest a then recent development from a flying ancestor.

References

Casuariiformes Ratites Prehistoric bird genera Eocene birds of South America Ypresian life Casamayoran Riochican Itaboraian Paleogene Brazil Fossils of Brazil Fossil taxa described in 1983 {{Paleo-bird-stub