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TARSITANO AND _MEGALANCOSAURUS_



>     I just got my JVP and SVP abstracts the other day.  I noticed that
>John Ruben is apparently now advocating Fedduccia's baby 
>Megalanica[big sic] as an alternative to theropods in bird origens.     

I did not get my SVP abstracts yet so I haven't read his reasoning.  I 
did read a bit in _Bioscience_ on Ruben's views on bird origins.  Ruben 
apparently thinks that _Megalancosaurus_ is a definitive proavis, even 
with a patagium.  Apparently, ANY small avian-like archosaur with 
arboreal features is an avian ancestor.  

And also, to be fair to Sam Tarsitano, the whole _Megalancosaurus_/ bird 
connection is pretty much his doing (and Rupert Wild).  In 1985 
(Archaeo. Conference Book), Tarsitano gave a progression as to how 
"thecodonts" can evolve into birds and _Megalancosaurus_ was hinted to 
be the first in such a series.  In _Origins of the Higher Groups of 
Tetrapods_ (1991), Tarsitano expanded the view more and said that most 
of the features that unite birds and theropods are found in 
_Megalancosaurus_, even a semi-lunate carpal.  

Basically, Tarsitano (1991) says that birds are some of the most basal 
members in the "Thecodontia" as evidenced by the plesiomorphic lack of a 
verticalized basioccipital (detailed in Tarsitano, 1985b), something 
that birds lack and all other archosaurs have except for 
_Megalancosaurus_.  He also discounts coelurosaurs from the ancestry of 
birds because they lack a siphonium (quadrate-articular pneumaticity; 
according to him is present in tyrannosaurs, which are coelurosaurs), 
"are too large to evolve flight", lack a fenestra "rotunda" (most 
authors contradict him and use fenestra pseudorotunda), and various 
other things.  

Matt Troutman


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