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Re: Phytodinosauria status

In a message dated 6/7/01 11:59:33 AM EST, qilongia@yahoo.com writes:

<< This trend is the major interpretation in loss of digits in tyrannosaurids 
and tetanurans broadly. >>

I think this interpretation may be incorrect. Note, e.g., that Carnotaurus 
retains four short ceratosaurian digits in an otherwise pretty useless 
(whatever that means) forelimb. I think digits are lost only when they are 
>positively detrimental<, not just useless. In other words, a forelimb with 
three digits will, when reduced, generally retain the three digits. 
Tyrannosaurids have two-digit manus because somewhere along the line the 
third digit got in the way of some function that was better done without it. 
I'm inclined to think tyrannosaurids are left over from an evolutionary 
experiment with two-digit wings in a group of dinobirds. Just "losing" the 
third digit for no apparent reason strikes me as odd, because this 
explanation does not favor the loss of the third digit over the other two. In 
other words, why didn't we lose digit 1 and/or digit 2 as well as/instead of 
digit 3?