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Re: More on Argentavis



Michael Habib wrote:

Granted, ostriches appear to be well above the maximum mass for a volant bird (though not the limit for volant vertebrates as a whole, see pterosaurs...), but many ratites are not. Am I mistaken in saying that the evidence suggests an increase to ostrich size *after* loss of volancy, rather than a loss of flight in the specific lineage leading to ostriches as size reached maximum launch limits?

I had the same thought. Ratites are almost always recovered as a monophyletic group, and the most parsimonious explanation is that flightlessness is primitive for the clade. Given the flight abilities of the tinamou, it may be that overall poor flight ability is primitive for palaeognath birds. I agree that loss of volancy almost certainly occurred prior to an increase to ostrich size.


The basal part of the neornithean tree seems especially prone to both loss of flight and impressive increases in body size; as well as ratites, we also have dromornithids and gastornithids (both regarded as galloanseraeans, or at least basal neognaths). It could be some ecomorphological pre-disposition to loss of flight + increase in body size; or it could just be opportunistic (i.e., lots of available ecological niches at around the same time); or just coincidence.

Cheers

Tim

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