Flightless bird
[1] There are over 60 extant species,[2] including the well-known ratites (ostriches, emus, cassowaries, rheas, and kiwis) and penguins.
[4][5] Divergences and losses of flight within ratite lineage occurred right after the K-Pg extinction event wiped out all non-avian dinosaurs and large vertebrates 66 million years ago.
New ecological influences selectively pressured different taxa to converge on flightless modes of existence by altering them morphologically and behaviorally.
The successful acquisition and protection of a claimed territory selected for large size and cursoriality in Tertiary ancestors of ratites.
[7] Temperate rainforests dried out throughout the Miocene and transformed into semiarid deserts, causing habitats to be widely spread across the growingly disparate landmasses.
Cursoriality was an economic means of traveling long distances to acquire food that was usually low-lying vegetation, more easily accessed by walking.
[8] Gigantism and flightlessness in birds are almost exclusively correlated due to islands lacking mammalian or reptilian predators and competition.
[12] Rather ratites arrived in their respective locations via a flighted ancestor and lost the ability to fly multiple times within the lineage.
[13] Ratites belong to the superorder Palaeognathae, which include the volant tinamou, and are believed to have evolved flightlessness independently multiple times within their own group.
[18] 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.
[11] Repeated selection for cursorial traits across ratites suggests these adaptions comprise a more efficient use of energy in adulthood.
All of these birds show adaptations common to flightlessness, and evolved recently from fully flighted ancestors, but have not yet completely given up the ability to fly.
[25] Although selection pressure for flight was largely absent, the wing structure has not been lost except in the New Zealand moas.
In a climatically stable habitat providing year-round food supply, a male's claimed territory signals to females the abundance of resources readily available to her and her offspring.
Similar to the emperor penguin, male ratites incubate and protect their offspring anywhere between 85 and 92 days while females feed.
[8] If no continued pressures warrant the energy expenditure to maintain the structures of flight, selection will tend towards these other traits.
[28] The only known species of flightless bird in which wings completely disappeared was the gigantic, herbivorous moa of New Zealand, hunted to extinction by humans by the 15th century.
Penguins are a well-known example of flightless birds.
Ostriches are the largest extant flightless birds as well as the largest extant birds in general.
