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Do the chromosomes of the kiwi provide evidence for a monophyletic origin of the ratites?



The extensive literature on the origin of the ratites focuses mainly on three questions: are the ratites mono- or polyphyletic, did they evolve from flying ancestors, and are they primitive or advanced? Opinion tends to accept a common descent from flying ancestors for the large ratites (for a summary of ideas see ref. 1). They would have evolved on Gondwanaland some time in the Cretaceous and have become dispersed over the southern continents after its fragmentation2,3. However, the position of the small New Zealand kiwis, in many respects the most peculiar of all birds, is still a matter for conjecture1,4. The chromosome complements of the large ratites have been found to be remarkably uniform5–8. The chromosome set of the kiwi, described here, clearly links up with these, which may be recorded as another indication for monophyly of all ratites. It also indicates that we are dealing here with very ancient karyotypes.


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