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Re: Holes in Frills



Peter Buchholz wrote:

> Possibly, but if that's the case, it makes one wonder why
> Triceratops closed up it's fenestrae when it's frill was
> proportionally as big (if not bigger) than most Centrosaurines.

The closure of the parietosquamosal fenestrae in -Triceratops- could indicate
a response to new predatory pressures (bigger tyrannosaurs?). The old frill
was, in most cases, somewhat fragile and of little use in defence. Also, it
might have been a response to the development of the unusually pronounced
brow horns in -Triceratops-, which must have played a role in intraspecific
combat. The parietal fenestrae of most chasmosaurines were not at great risk
from the usual nasal horn, but dueling -Triceratops- might easily have
inflicted life-threatening wounds on one another with those brow horns, if
their frills were fenestrated.  So, the solid frill might have evolved
concomitantly with the large brow horns (I favour this second explanation
myself). And as I said before, the loss of the fenestrae, the built in
weight-reducer, would be inherently offset by the large brow horns
themselves, *allowing* the fenestrae to close. The weight problem is further
offset by the recurving of the frill's rim.

> Although I don't doubt that they were used for other purposes like
> display and possibly defense, I think that their primary function
> was for making them bite hard.

Though I am not familiar enough with the particulars of ceratopsian cranial
musculature to get too deeply into this, we have to keep in mind that
providing for a *longer* adductor muscle would not have resulted in a
*stronger* bite. And how strong does a ceratopsian's bite need to be, anyway?
Were they the beavers of the Late Cretaceous?

> As for the horns counter-balancing the frill...  Wouldn't something
> along the lines of Pachyrhinosaurus' nose be more economical if
> that's what the horns were for rather than an aray of wildly
> different horns?

As I said above, the horns would not have evolved *for the purpose* of
counter balance, but would have bestowed that advantage regardless. And
evolution is, by no means, tied to human concepts of economy. One can almost
always conceive simpler solutions than the ones that appear to have actually
occurred. Evolution is not parsimonious. To paraphrase Gould (paraphrasing
Jacob): Nature is a superb tinkerer, not a "divine artificer."

> Again, I believe that the primary function of the horns was for
> either display or defense (intra-or inter-specific), and the
> possible counter-balancing effects were a nice extra.

This may well be the case (I suspect it is), that larger and larger horns
were selected for defence and display, and not counter balance, that they
pre-adapted the skull for closure of the fenestrae. But this seems to be one
of those chicken/egg which-came-first problems. How do we determine which
function of a character bestowed its primary selective advantage?

Caitlin R. Kiernan