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Even more concerning the Triceratops/Torosaurus deal
1st note. BYU specimen was examined by Scannella. Just in case any of you were
I'm not addressing any questions concerning unpublished research. However some
discussion on Horner & Goodwin's recent paper:
David Marjanovic wrote:
<*Triceratops*, where the epiparietals and -squamosals start as pointed
(..."acuminate", if you prefer) osteoderms, then fuse to the skull and each
other, and then become broader and very blunt.>
>Unlike in *Triceratops* where the authors propose that the epiparietal and
>episquamosal spikes are fused to the frill and the sutures are obliterated
>..... Thus the dimensions of the epis are UNKNOWABLE unlike in the spikes, as
>their limits are now absent. Moreover, >the determination that the gross
>dimensions of the epis both broaden cirrcumferentially (for want of a term,
>around the margin of the frill) and shrink in basoapical "length" while the
>metaplastic frill enlargement subsumes the bases of the epis coincidentally
>obliterates >the very data used to project the dimensions in the first place.
>These two cases are NOT analogous, even if they are both metaplastic.
I think you need to look at some actual triceratops material. If you read
through horner & goodwin (2006, 2009), you will find that epis only fully fuse
on to the frill very late in ontogeny. Early in ontogeny they are narrow and
very pointed: delta shaped, and are not fused to the frill margin (hence they
are rarely found). Anyhow, even when the epis fuse on (or start to fuse on) you
can clearly see the margins of the epi in question, so the above suggestion
that the limits are "UNKNOWABLE" is false.
> Moreover, the authors also project sequential metaplastic growth, then
> erosion, and argued that irregularities in the interface between osteoclastic
> and nonosteoclastic bone support this, but this can also occur with increase
> in invagination of the surface of the bone >via nutriating tissues and blood
> vessels (underlying the keratinous sheath) as they themselves argued in
> late-stage metaplasia. A dis
the two types of bone, rather than regular deposition, is hardly direct
evidence of erosion, nor does it explain >osteoclastic bone erosion while
metaplasia was underway, when metaplastic transformation is to occur afterward
(while the structures were still apparently horn-like).
Again, read the triceratops paper. Trike horns change orientation through
ontogeny, that means they ERODE bone on one side, and DEPOSIT bone on the
other. That's how it works.
<Or, alternatively, sexual selection is just a bit more complicated than we
used to think.>
> You know, I recall having discussions that projecting extant analogues was
> the only way to KNOW the constraints under which systems can work. Witmer and
> Holliday studying bone analogues for soft-tissues, Taylor et al studying
> aniaml neck posture, Hutchinson and Gatesy et als on locomotion of various
> tetrapods. Eliminating what doesn't work, to narrow the field to what does.
> Instead, the above quote purports that we can just toss in an idea because it
> _isn't contradictable_; tantamount to asking "why not?" This is science?
Dinosaurs were not deer. Some people seem to have a great deal of trouble
accepting that fact. Modern savannah/grass based ecosystems may not be good
analogues for mesozoic ecology: you wouldn't compare dinosaur ecology to that
found in carboniferous swamps, so why do you think it is any more appropriate
to assume that it was similar to what we see today in entirely unrelated
animals? There are benefits to using comparative anatomy, of course, but there
are also severe limitations, and these can be very misleading. Proposing
comparative anatomy as the "only" way to "know" doesn't sound like science to
me. Anyway, if you really want a deer comparison... what age deer has the best
rack? Through ontogeny, (up to a point (!)) deer get more points on their
antlers, which are shed each year: deer don't even bother to erode (=resorb)
all that good phophate.
<Does "a single taxon must arise from any development" mean anything? Because
if so, I can't figu
> I may have missed a "-al projection," which would have alluded to my
> understanding that ontogeny is not a proxy for phylogeny, but must derive
> from it nonetheless (ontogeny in the constraints created by phylogeny,
> whatever they are, while phylogeny will enforce by common descent similar if
> not identical ontogenetic trajectories as the null model). The paper proposes
> that it can do away with the null hypothesis by working itself backwards --
> that there is a minimal number of taxa, and that metaplasia is the result of
> distiguishing features among age-classes. This is not to say that I prefer
> taxonomic profusion, and am a conservative lumper by concern, rather than
> practice; but simply trying to shoehorn specimens into an ontogenetic scheme
> and say that the ontogenetic scheme supports the shoehorning is certainly not
> a safe ground.
Why is taxonomic diversity the null hypothesis? Frankly,
always-cladogenesis/diversity is unfalsifiable, therefore unscientific. There's
a lot of good data that corroborates Horner & Goodwin's views, but you will
have to wait for the paper. Dinosaur taxonomy as we know it, is going to change.
> I would suggest looking up the work Lehman has done to clarify the taxonomic
> disparity among different areas in similar ages of the latest Cretaceous. It
> was certainly not one "narrow strip of forested floodplain," and we are
> cautious about assuming that all taxa recovered where we have originated in
> that region. Simply examining the veldt or Serengheti will provide a
> diversity of Bovidae in what is "just one big savannah," by comparison.
See my above comment. I have presented at SVP on why most of what Lehman
published on the biogeography issue is incorrect. Adherence to these old views
holds back our understanding of what is going on. You'll see much more on this
issue presented and published over the coming few years.