''Diogenornis'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

ratite A ratite () is any of a diverse group of flightless, large, long-necked, and long-legged birds of the infraclass Palaeognathae. Kiwi, the exception, are much smaller and shorter-legged and are the only nocturnal extant ratites. The systematics ...

s, that lived during the

Early Eocene In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian i ...

(

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

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 Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...

.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 list of fossiliferous stratigraphic units in Brazil, fossiliferous geologic Formation (geology), formation and LagerstätteKellner & Campos, 1999, p.399 of the Itaboraí Basin in Rio ...

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 specimen ...

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, 188 ...

.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 Cassowaries ( tpi, muruk, id, kasuari) are flightless birds of the genus ''Casuarius'' in the order Casuariiformes. They are classified as ratites (flightless birds without a keel (bird anatomy), keel on their sternum bones) and are native t ...

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 The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

.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 (biology), order of birds called Tinamiformes (), comprising a single family (biology), family called Tinamidae (), divided into two distinct subfamily, subfamilies, containing 46 species found in Mexico, Central America ...

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

, 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