Re: Son of Ceratopsian forelimbs

["Matthew Bonnan" <mbonnan@hotmail.com>]

Andy Farke says:
> Also, what of the crossed radius and ulna illustrated in the [Paul and 
> Christiansen] paper? I don't
> know of a single articulated ceratopsid skeleton that supports this.

Yes, thanks for pointing this out.  Even if the glenoids faced directly 
ventrally (which they don't), the radius does not cross the ulna and 
therefore the hand (manus) would end up facing sideways, not anterolaterally 
as the tracks suggest.  Paul and Christiansen seem to think that the radius 
should have crossed over because you need the distal end of the radius 
medial to the distal end of the ulna in order to turn the manus forward as 
it is in the trackways.  This is sort of putting the cart before the horse, 
assuming that the only way to turn the hand forward is to cross the bones.  
You can also get the hand to turn forward if the radius and ulna remain 
uncrossed and you have a semi-sprawled forelimb.  To their credit, they 
admit that radial crossover of the ulna is subtle, but so far as I can tell, 
the only way to cross the radius over the ulna as they illustrate is to 
disarticulate it from the ulna and force it into a crossed position.

Matt Bonnan
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