Re: Claws on deinonychosaurs (oops)

["Jaime A. Headden" <qilongia@yahoo.com>]

Phil Bigelow (bigelowp@juno.com) wrote:

<On a related issue, does anyone have any explanation(s) as to why a serrated
cutting edge never evolved on the deinonychosaurs' curved claws?>

  Would you expect to find this on the ungual, or the sheath?

<Or did it evolve?  Maybe only the keratin sheath expressed the serrations? 
What is the evidence from the Chinese material that shows well-preserved
integument?>

  Serrated edges appear on the specialized "comb" of some landfowl, but
otherwise, I believe that the development of serrae on feline sabres are
actually a secondary developmental issue to sabre formation. They are costly to
develop in teeth, differentiation of cusping and forming dentine beads in
animals like *Smilodon*. The keratinous serrae in whipporwhils, some
strigiforms, and apparently herons and junglefowl, are elaborated on the sides,
rather than venter, as in this animal:

  http://placeforwildbirds.tripod.com/whip4.jpg

  Their function likely elaborated scratching behavior with irregular features
of the sheath of claw to "comb" feathers, and selected for fewer parasites and
thus survival.

  The shape of these claws, broad and not strongly curved, likely suggests the
same morphology of the keratin was not present. Ungual sheaths in similar
animals, such as *Microraptor* and *Archaeopteryx* suggest the sickles may not
have had serrae, but this is inferrence based on phylogeny, not based on
positive data.

  Cheers,

Jaime A. Headden

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


        
                
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