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Re: Horner's Pachy Lumpin' - Your Thoughts?



-- On Sun, 1/10/10, David Marjanovic <david.marjanovic@gmx.at> wrote:

> >  Is this true in the case
> where the horns are also rapidly enlarging?
> >  It would seem in that case that merely
> increasing deposition on one
> >  side would change curvature w/out any removal
> required.

> That would result in an S-shaped horn, and that's not what
> we see. Instead, the horns first curve backward, then they
> stick straight up, and then they curve forward.

An S-shape? Not necessarily, in the case where diameter is increasing as well 
as length. The "old" curve can be easily swamped, at least in trees, by 
asymmetrical diameter growth. It is still there, but is buried underneath new 
growth. 

Curvature reversal is often seen in logs. Lengthwise slicing along pith center 
brings it out nicely (personal obs.). 

However, who cares? Curvature reversal is not needed to prove the resorption 
case as mentioned by others previously. 

> >  Further -- I wonder if backwards curving horns
> in juveniles is
> >  mentioned in lit as support (on a selective
> basis) for the 'extended
> >  close physical adult/offspring contact'
> scenario. Perhaps hunkering
> >  underneath Mom for protection from sun, weather,
> and predators (etc)
> >  was better tolerated by Mom if your little horns
> did not stick
> >  STRAIGHT up... :D

> Who knows! :-)

Heh. Well, somebody probably does. Note I asked if the (I assume  untestable) 
concept is mentioned in print, not if it actually occurred. 

> Regarding horn resorption in *Pachyrhinosaurus*, this looks
> to me like the horn core was resorbed while the keratinous
> horn stayed; counterintuitive enough, but perhaps it
> suggests the same for *Pachycephalosaurus*.

Stressing I have NO opinion re lumping/splitting, etc, I do not find horn size 
reducing w/ age, or even disappearing entirely, to be particularly 
"counter-intuitive". Taking a case where the horns and frill are assumed to be 
defensive in function* (for example), it could imply a "social" structure 
wherein older animals were not active in
ng to herd center or even being outcast, perhaps depending on reproductive 
assumptions. 

There may not be an extant analogue, but so what? Is there a dinosaur that grew 
annual antler-analogs? Should we assume one existed, just because we now have 
elk? Lack of extant analog isn't a very strong argument, barring some apparent 
violation of physical laws.  

*I note that the frill is intimidating in appearance, especially from the front 
view, even if it has no real function as armor.