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Re: Ah ha! That's where therizinosaurs came from

>> Secondly, failure of any recent group of flightless birds to
>> spread over the world is in part due to the recent positioning of
>> the continents (ie there are oceans in the way). Presumably
>> flightless birds have only dispersed over a land connection (I
>> can't think offhand of an example of a flightless bird spreading
>> by, say, rafting).
> Gondwana and Lauarsia were separated, but they shared several
> groups of maniraptorans in common.

That separation only came about in the Late Jurassic and was rather intermittent. In contrast, I don't think there ever was a unitary Laurasia that wasn't cut in two by various seas through Europe.

>> Third, the fauna of mammalian predators and nest-robbers has been
>> quite different since the K-T from what it was earlier, and the
>> barriers to radiation of flightless birds on continents may not
>> therefore be identical to what they might have been in the
>> Mesozoic.
> Different, certainly, but there is no reason to think the
> differences were consequential. Mammals were feeding on dinosaurs
> in the Mesozoic, they could glide, they could swim, no reason to
> think they couldn't rob nests.

Never mind nest robbers. It now seems that the flightless paleognaths became flightless in the early Paleocene on the continents as if they were islands -- due to the lack of big predators after the K-Pg mass extinction.

> But, in the case of rails, the morphological changes
> associated with flightlessness were so recent and superficial that
> the resulting species did not move into new families, unlike with
> the ratites. In maniraptorans we had, I guess, Troodontidae and
> Dromaeosauridae that Paul might say descended from Archaepterygids,
> though he may group them all in the same family.

Isn't that just a matter of time? Let those flightless rails sit on their islands for 30 million years (...longer than most of the islands in question will exist, but never mind...) and then tell me what ranks you'd assign to them.