''Rhea fossilis'' is an extinct species of

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

in the genus '' Rhea'' that inhabited the Southern Cone of

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

during the

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

period. Its closest living relatives are the

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 ...

and the

lesser rhea Darwin's rhea or the lesser rhea (''Rhea pennata'') is a large flightless bird, the smaller of the two extant species of rheas. It is found in the Altiplano and Patagonia in South America. Description The lesser rhea stands at tall. Length ...

Naming and discovery

''Rhea fossils'' is only known by a couple of fossils, a

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

and

tarsometatarsus The tarsometatarsus is a bone that is only found in the lower leg of birds and some non-avian dinosaurs. It is formed from the fusion of several bones found in other types of animals, and homologous to the mammalian tarsus (ankle bones) and meta ...

, discovered by Alcide Mercerat and

Francisco Moreno Francisco Pascasio Moreno (May 31, 1852 – November 22, 1919) was a prominent explorer and academic in Argentina, where he is usually referred to as ''Perito'' Moreno (''perito'' means "specialist, expert"). Perito Moreno has been credited as on ...

in 1891. They were some of the first paleontologists to describe and catlouge the rhea fossil record. From the fossils found, he and Mercerat determined it to be a transitional species between the greater rhea and the lesser rhea. They also inferred it was the same size as modern-day rheas.

Paleoecology

''Rhea fossilis'' is very similar to its extant relatives, albeit slighter more slender. It inhabited the grassland and scrub forest of the Pampas region of Argentina. During this time, the area was warmer and wetter than it is today. Like its living cousins that still inhabit the region today, it fed on broad-leaved plants, fruits, seeds, and small animals, such as

lizards Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia althou ...

. ''Rhea fossilis'' would have likely been preyed upon by

terror birds Phorusrhacids, colloquially known as terror birds, are an extinct clade of large carnivorous flightless birds that were one of the largest species of apex predators in South America during the Cenozoic era; their conventionally accepted temporal ...

and other

apex predators An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...

of the region.

References

{{Taxonbar, from=Q111479899 Rheidae Birds