Re: Fastovsky vs. Archibald

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

Matias Soto (soto@adinet.com.uy) wrote:

<I hope a high DSDI is still characteristic of Microraptoria + Dromaeosauridae
(unless you consider Richardoestesia, Dryptosaurus, and basal/juvenile
tyrannosaurs, am I right?).>

  Why do you say "hope"? There is a functional advantage for this in
dromaeosaurs that so far does not occur in sufficiently interpolated close
outgroups to prevent this feature from being autapomorphic of the
microraptor-dromaeosaurid clade (which may now need a name).

  If the base of a denticle is larger given a size for the denticle (say,
base-length:volume, this has obvious functional advantages in reducing torsion
and shear during puncturing. This is present in the smaller denticles (usually
more basal than apical) in troodontid teeth, but these are also less hooked
than the more distal denticles. The advantage is resistance, and there are
reasons for this in tough flesh, struggling prey, or perhaps most especially,
small prey. But this requires coupling of the base-length:volume metric with
the shape of the denticle (a rounded, non-apicular denticle as in tyrannosaurs
and *Richardoestesia* lacks advantage in individual-denticle piercing, but is
good in slicing/whole-tooth piercing as it permits the denticles to combine and
form a sort of "carina" that keeps the tooth running in a particular course
during the bite), and this is influenced by the other taxa that possess the
other features. This does not mean the feature is not phylogenetically
informative, however.

  Cheers,

Jaime A. Headden

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