Rhea (bird) to be growing. The genus name was given in 1752 by Paul Möhring and adopted as the English common name. Möhring named the rhea based on the Greek Titan Rhea, whose name is derived from the Greek "Rhea" () from έρα "ground". This was fitting with the rhea being a flightless ground bird. Depending on the South American region, the rhea is known locally as "ñandú guazu" (Guaraní, meaning big spider, most probably in relation to their habit of opening and lowering alternate wings when they run), "ema" (Portuguese), "suri" (Aymara and Quechua), or "choique" (Mapudungun). "Nandu" is the common
Flightless bird the lineage. This indicates that the distinctive flightless nature of ratites is the result of convergent evolution. Two key differences between flying and flightless birds are the smaller wing bones of flightless birds and the absent (or greatly reduced) keel on their breastbone. (The keel anchors muscles needed for wing movement.) Adapting to a cursorial lifestyle causes two inverse morphological changes to occur in the skeleto-muscular system: the pectoral apparatus used to power flight is paedorphically reduced while peramorphosis leads to enlargement of the pelvic girdle for running. Repeated selection for cursorial traits across ratites suggests these adaptions comprise a