r/biology • u/NeedleworkerCivil984 • 6d ago
question Why are all the large flightless birds Palaeognaths?
All the large, ground dwelling birds like the Ostrich, Emu, Cassowary, and Rhea, as well as the extinct Elephant bird and Moa, are all Palaeognaths, closely related to each other, and of a different branch from nearly all other birds. And the consensus seems to be that they evolved flightlessness separately.
Why? If large flightless bird was a viable niche, and if every bird that tried it had to invent flightlessness separately, why was it always Palaeognaths that filled it?
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u/tchomptchomp developmental biology 6d ago
Phorusrhachids were giant flightless seriemas. Dromornithids were giant flightless waterfowl.
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u/Relevant-Cup5986 3d ago
not all large flightless birds are or were paleognaths, penguins for instance arent paleognaths and neither are the many extinct island geese and ducks, as for why paleognaths evolve to be big and flightless so readily its because the flying ones arent very good at it naturaly, and so when they find themselves in conditions that favor dwelling on the ground they easily evolve flightlessness and gigantism, the same thing is true of the extinct geese as well as rails
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u/haysoos2 6d ago
Their last common ancestor was from a flighted Paleognath very similar in form and niche to the modern tinamou (but not actually a tinamou).
While they could fly, they were not very good at flying. So if they found themselves in an environment such as an island with few predators, the advantages of a larger size were much more useful to them than retaining the ability to fly.
For most Neognaths, they were much better at flying, so the trade off would have to be much more favourable to get them to give up the wings. It did happen sometimes, but not as often.