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Re: Velociraptor furcula



In a message dated 96-12-02 17:31:10 EST, longrich@stardot.com (Nick
Longrich) writes:

>       What's got me puzzled right now is why Velociraptor doesn't have a 
> furcula. Oviraptor has one, T. rex has one, even Allosaurus has one, but 
> apparently the articulated "fighting" specimen doesn't. Is it really 
> absent? I did read something in the photo caption about it being a 
> "juvenile" specimen, so perhaps it wasn't fully ossified, but it looked 
> pretty well grown to me. Whatever the case, its recent ancestors must 
> have had one, or else we'd have to postulate at least three independent 
> evolutions of the thing, and it's vastly easier to assume that it was at 
> least present at the allosaur-coelurosaur node or earlier. 

The furcula most likely appeared somewhere between the branch-off of the
phytodinosaurs (in which furculae are unknown whereas clavicles are known)
and the primitive avian _Longisquama_, which sports a well-documented furcula
almost identical in shape to that of _Archaeopteryx_ and other theropods.
Unfortunately, it seems too easy for a furcula to evolve by fusion of the
clavicles for it to be a nail-it-to-the-wall character, diagnostic >only< of
avians (theropodomorphs, but not other kinds of dinosaurs, included here),
but it's pretty good.