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New Velociraptorine



[ I think where Nick says "Tib/fib" he means "femur/tibia".  The tibia
  and fibula of the new beasty are approximately the same length.  The
  femur is shorter than both; judging by the scales next to the
  individual bones, the 0.56 seems about right (ignoring the curvature
  of the femur and just taking the distance between its endpoints).
  -- MR ]

        I went and found the critter online. It didn't immediately strike 
me as being expecially long-armed, although it does indeed have an 
incredible tib-fib ratio. Here's the stats I got. It's just done 
with a ruler and some pictures and not fantastically accurate, but it 
should serve for a preliminary report.

  Tib/fib ratio of dromaeosaurs:

Velociraptor: .97
New Dinosaur: .56   <--?!
Deinonychus:  .89

Next I compared humerus+ulna/femur+tibia

Velociraptor: .55
New Dinosaur: .66
Deinonychus:  .66


Which isn't all that meaningful, I mean, storks and secretary birds 
probably have a low ratio compared to an albatross. So that's probably 
not all that interesting. 

Finally, what is probably a much better measure of the relative size
of the arms, the ulna+humerus/scapula ratio.

Velociraptor: 1.65
New Dinosaur:  2.09
Deinonychus :  1.83


That's 126% of V. mongoliensis, 114% of Deinonychus for arm length. I 
used GSP's skeletal illustrations (BTW a friend finally found PDW for me! 
 And in a truly weird turn of events, I am allowing a Japanese 
company to distribute my Mac icons in exchange for the Complete Illustrated 
Guide and some origami paper :) Ah, free enterprise...) 

If I had it handy, I would include Archaeopteryx in here. But my first 
impression and the argument put forward by these numbers is that this 
isn't an incredibly long-armed theropod like Archaeopteryx. It does show 
that Deinonychus is relatively long-armed, Velociraptor, relatively 
short-armed for a dromaeosaur, and that this thing has the longest arms 
of all, by a narrow  margin. I don't think that Achaeopteryx is a great 
comparison. And it does indeed have quite a short pubis. 
        This doesn't mean it couldn't be some kind of flying animal (it 
does appear to have the stiffening rods of dromaeosaur tails, so it is 
probably closer to these than the Madagascar bird) something along the 
lines of a secretary bird. Dromaeosaurs may have been pretty diverse. But 
I don't think that this fossil argues for  that especially either. The 
thing that seems to be truly unusual about this animal is its hindlimbs. 
Any thoughts on why such a small tib/fib  ratio and small pubes would be 
useful?
        
        Nick Longrich