Ostriches, emus, rheas and other large, flightless birds are found on six landmasses separated by oceans, but how they reached such far-apart places without the ability to fly has remained an enduring mystery.
One idea was that the ancestors of this group of birds, known as paleognaths, just walked to those locations when most of the planet was harnessed together as the supercontinent Pangaea (320 million to 195 million years ago) and that, when this giant landmass split up, the birds were already in those locations.
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