Re: Moasaurus

["Tim Williams" <twilliams_alpha@hotmail.com>]

Mike Eagle (perhaps a Kiwi himself  :-) ) asked about the moa:


> Was it really a "bird", or was it a true dinosaur

Yes and yes.  The thing is, if birds are derived from dinosaurs (as the
available evidence suggests) then birds themselves must be considered
to be dinosaurs.

> I'm not an ABSRD (anything-but-a small-running-dinosaur) advocate, neither
> am I a BAND (birds are not dinosaurs) fan.

ABSRD and BAND are one and the same.  I coined the former to highlight the 
fact those who dispute (vociferously) the origin of birds from dinosaurs 
have yet to come up with an alternative ancestor.  Until they do, I find 
their scenario extremely wanting.

> Moa posessed no wing bones (not even vestigiel ones); [...] had a "stringy" 
> type of feather more suited to body insulation / protection than flying; 
> laid large eggs in a ground nest;  [snip]

I think the same is actually true for kiwis too.

With respect to the dinosaurian afinities of moas, you bring up an 
interesting point.  If certain birds did become secondarily flightless, 
would we mistake them for nonavian dinosaurs?  For example, perhaps the 
moas' total absence of forelimbs indicates a stage in evolution one further 
than the tyrannosaurids - dispensing with forelimbs altogether.  Perhaps the 
hairlike feathers of moas and kiwis are primitive features, like the 
hair-like integument structures ("dino-fuzz") of certain small nonavian 
dinosaurs (_Sinosauropteryx_, _Sinornithosaurus_ etc) from China.

But with moas (Dinornithiformes) and other ratites I think we're on pretty 
safe ground.  Their feathers may be hairlike, but their skeletal anatomy 
puts them well within the Aves.  Same with penguins and the dodo.  Ratites, 
penguins and the poor old dodo all share more features with modern flying 
birds (gulls, ducks, hawks, titmice, swallows, cotingas, boobies, sparrows, 
auks, tinamous, owls, chickens, pigeons etc etc etc) than they do with 
extinct theropod dinosaurs.  Therefore, moas are currently placed inside the 
Aves.  Their closest relatives are the other ratites (kiwis, ostrich, emus, 
cassowaries, rheas, elephant bird).

Interesting question though.

> The more I consider the evidence,
> such as the advanced aerodynamics of Archaeopteryx feathers, I too tend to 
> think that some birds may have begun to evolve sometime in the Middle to
> Late Triassic.

_Archaeopteryx_'s skeleton though is far less bird-like than its plumage.


Tim

P.S. By the way, I stopped by New Zealand on my way home to Sydney two years 
ago.  Beautiful country.  Now, what's this I hear about NZ becoming the 
seventh state of Australia...?

;-)


------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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