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Re: Claw function in Deinonychus



Michael Mortimer (mickey_mortimer111@msn.com) wrote:

<As total length is uncertain for all except a few complete dromaeosaur
specimens, perhaps a comparison of ungual length to another element's length
would be less prone to error.>

  While this is certainly true, as noted in the last posts by Mike Habib and
myself, there is a signal albeit a weak one, based on the specimens involved
in. The reason I used body length is that it may more accurately capture mass
estimation and thus applicable to the hypothesis of weight-bearing pursued in
the thread. The use of other elements must bear directly on this issue for
utility, or apply in a way to demonstrate functional applications. The rest may
be phylogenetic, but their functional effects are lost, perhaps. In this case,
humeral and/or femoral circumference will better capture such a signal, but for
it's size, at 2/3 the length, *Velociraptor* has a much more robust femur than
does *Deinonychus*, given the diameter in lateral view versus it's length. This
has the effect of perhaps increasing *Velociraptor* mass inch for inch greater
than in *Deinonychus*. The elongated, more slender femora of smaller paravians
such as *Achaeopteryx* lack many of the weight-bearing issues for being less
than 1/10th the size of *Velociraptor*, for example. So are these phylogenetic,
size-based, or functional?


  Here's data comparing ungual length to femoral and phalanx II-1 length. 
Velociraptor's and Deinonychus' femoral lengths are estimated from scaling
similar-sized specimens, as no single specimen has been measured for all
relevent elements.  Utahraptor material is not articulated and lacks described
pedal phalanges or femora.  I included Archaeopteryx just to see where it'd
go.>

<Sinornithosaurus
 holotype- ungual 35, phalanx 15, femur 148>

  Which ungual was this again? As in my previous posts, one projects certain
inconsistencies when measuring incomplete elements. Even using "Dave" as an
example, mdII-3 measures 15.26mm, while pdII-3 measures ~15.7mm, so that
maintaining this ratio (1.02) in the supposedly adult form of the possibly same
species, *Sinornithosaurus* ends up with a mdII-3 predicting a pdII-3 of only
~26mm (as noted, I increased the percentage by 10%, not 2%, and an estimate for
the missing tip of pdII-3 and greater accounting for the ungual length in
"Dave" gives me a ration of 4-5% more, so this would still only account for
26.75mm (I was clearly quite generous). Since these two specimens are almost
nearly the same size in some of their proportions and elements, it is either
unlikely they are actually the same species, but they may be the same "genus",
or that limb-based allometry was slow and the remainder grew quickly, based on
total size comparison. Unfortunately, as in *Sinornithosaurus*, femoral length
is estimated based on incomplete epiphyses (in *Sinornithosaurus*, it is the
distal femur that is missing, while in "Dave" it is the proximal femur that is
either missing or obscured).
 
<Based on this, I'd agree comparative ungual length increases with body size, 
albeit not by much.  Bambiraptor has an unusually large ungual for its size, 
while Adasaurus has an unusually small one.>

  Which fortunately agrees with my previous estimations based on projected body
length, though the voluminous estimation of gross body length does interfere in
the estimation process. Determining mass and calculating claw size versus mass,
measuring claw curvature, and relative robusticity, are in fact be better
metrics than employed so far by any of us.

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


        
                
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