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Re: Even more concerning the Triceratops/Torosaurus deal
Jaime Headden wrote:
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(Just for the record: the above suddenly appeared as part of the text
when I hit the "reply" button.)
bstantial amount of the paper is taken to demonstrate metaplastic transform=
ation and development of the horns and domes in *Dracorex* and *Stygimoloch=
*=2C and from this the authors conclude that they are synonyms (apart from =
rather aberrant and unique open sutures in the dome of the latter=2C which =
diverges from all other so-called incipiently domed juvenile or subadult pa=
chycephalosaurids known to date)=3B moreover=2C they then note that *Pachyc=
ephalosaurus* itself is the largest roadblock to synonymizing these taxa in=
to it=2C such that the squamosal nodes are not even spikes but large knobs =
(with a broader circumference around the base than in *STygimoloch* OR *Dra=
corex* squmaosal horns=2C are rounded or bluntly accuminate=2C and much sho=
rter than the horns of the other taxa). They invoke metaplastic shange to r=
esult in this=2C along with erosion of the horns into knobs=2C but do not d=
emonstrate a parallel to test this hypothesis.
*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.
Essentially=2C the paper tak=
es us on a faith-based argument that metaplasia + erosion DOES result in th=
is transformation=2C and ignore the functional concerns that contradict the=
theory (secondary sexual seletion should result in a seeming reverse trans=
formation than they offer: knobs into spikes) for the sake of the fine hist=
ological work (which I do not have an issue with. The authors seem to push =
(from almost the first paragraph of the introduction) that the synonymy is =
real=2C and go about detailing the evidence FOR=2C but not AGAINST.
Or, alternatively, sexual selection is just a bit more complicated than
we used to think.
=A0 The reason I bring this up is that I should hope the currently pending =
work on chasmosaurine ceratopsids does not also fall into this argument=2C =
for I consider this work (fine) to be lacking in replicatability. Implicit =
in the argument is that the metaplastic transformation (and erosion thereaf=
ter) of the ornamentation in ceratopsids and pachycephalosaurids is used to=
imply that a single taxon must arise from any development=2C
Does "a single taxon must arise from any development" mean anything?
Because if so, I can't figure out what. Please help me out.
and that beca=
use of this=2C the condition precludes the existence of multiple sister tax=
a (even coevals) with the same ontogenetic trajectory or metaplasticity dur=
ing growth. We are to assume that because they may be representative of a g=
rowth series=2C they represent the _same_ growth series of a single taxon. =
It beggars the imagination to assume that taxonomic diversity is so low for=
a highly ornamented clade=2C unlike the observed specific variation only a=
I don't think that's a good comparison. We're talking about just one
ecosystem, one long but narrow strip of forested floodplain. I don't
expect high diversity of anything there.
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