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

[Jason Brougham <jaseb@amnh.org>]

> OK, I take your word for it that moas spanned the same range of body size as 
> Microraptor Zhaoianus and Utahraptor, and had morphologies as different as 
> Balaur and Mahakala. 
> 
> I guess my point here is that there are differences, and as far as global 
> distribution it sounds like we agree. Whether they are meaningful differences 
> that falsify the BCF hypothesis is a much more complex matter and, I admit, 
> the difference in global distribution, alone, is not a very strong argument.
> 
> How old are the first moas, any idea? Because dromaeosaur teeth are known 
> from the Jurassic and go right up to the KT.
>  
> On Aug 9, 2011, at 5:45 PM, Ronald Orenstein wrote:
> 
>> Leave out "achieved worldwide distribution" and the moas come pretty close.
>>  
>> Ronald Orenstein
>> 1825 Shady Creek Court
>> Mississauga, ON L5L 3W2
>> Canada
>> ronorenstein.blogspot.com
>> From: Jason Brougham <jaseb@amnh.org>
>> To: david.marjanovic@gmx.at
>> Cc: DML <dinosaur@usc.edu>
>> Sent: Tuesday, August 9, 2011 4:57:17 PM
>> Subject: Re: Ah ha! That's where therizinosaurs came from
>> 
>> Yes, let's keep the point in mind: that no family of ratites or other 
>> flightless crown group birds that I am aware of has become flightless, 
>> achieved the morphological distinction of a new family, and then radiated 
>> widely, diversified, achieved a range of body sizes spanning two orders of 
>> magnitude, and achieved global distribution, in the way that dromaeosaurs 
>> did, if we assume that BCF is true.
>> 
>> 
>> On Aug 9, 2011, at 4:26 PM, David Marjanovic wrote:
>> 
>> >> >> 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.
>> 
>> Jason Brougham
>> Senior Principal Preparator
>> American Museum of Natural History
>> jaseb@amnh.org
>> (212) 496 3544
>> 
>> 
>> 
>> 
> 
> Jason Brougham
> Senior Principal Preparator
> American Museum of Natural History
> jaseb@amnh.org
> (212) 496 3544
> 
> 

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544