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RE: Horner's Pachy Lumpin' - Your Thoughts?
Michael Erickson <email@example.com> wrote:
> The structures (pachycephalosaur horns and
> ceratopsian epoccipitals) are not even homologous. Rather,
> we have numerous examples, from both extant and extinct
> taxa, that demonstrate that horn reversal during ontogeny is
> not at all normal or natural for any terrestrial tetrapod.
> We can even use the _Triceratops_ analogy as evidence
> *against* Horner's proposals, for although the brow and
> nasal horns of _Triceratops_ change shape significantly
> during ontogeny, there are no reversals or reabsorbtions. In
> terms of size, the horns just keep getting bigger and bigger
> until they are at their longest and largest in fully grown
Well, not exactly. Horner &c argue that that there is a resorptive
contribution to this change of shape ("eroded as they reduced dorsoventrally").
This is why I quoted their text. You may or may not accept their
interpretation. But, whether 'eppocipitals' and 'horn cores' are homologous is
largely irrelevant, because Horner &c at least offer a precedent for the
*principle* of the resorption of osseous tissue during ontogeny.
Overall, as others have said, I think the best way (in fact, in a scientific
sense, the *only* way) to refute Horner &c's hypothesis is to assemble data
that supports an alternative hypothesis. Simply accusing a hypothesis of being
"counter-intuitive" serves no purpose at all, and only produces more heat than
light. To switch to a well-worn argument, how many times has an
terrestrial/cursorial ("ground-up") origin of flight been crititized as being
"counter-intuitive"? It's not a valid scientific argument, and never has been.