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RE: dracrorex and National Geographic
Denver Fowler wrote:
> Well.. the nodes are identical in arrangement, and dracorex, stygimoloch, and
> pachycephalosaurus are all most likely from the same stratigraphic interval.
> Dracorex and
> stygimoloch are both non-mature.. which raises the question as to whether you
> can erect a taxon
> based on immature specimens. What happens if a taxon is first defined on a
> juvenile, then an
> adult morph is found, with quite different morphology... do you change the
> holotype to the adult
> but keep the juvenile name; or do you sink the juvenile (yet senior) name
> into the adult name.
In this case, if the immature specimen is diagnostic at the species or genus
level (and the two species can therefore be *demonstrated* to be conspecific or
congeneric) then its name gets priority over the adult. This is what happened
with _Apatosaurus_ vs _Brontosaurus_; the former has a subadult individual as
its holotype, but this didn't prevent _Apatosaurus_ from being awarded priority
On the other hand, some genera and species that are based on juvenile or
subadult material cannot be diagnosed at the species or genus-level, and
therefore become nomina dubia. This happened with certain ceratopsian and
hadrosaur genera: the immature specimens lack diagnostic characters that can be
used to tie them to taxa based on adult/diagnostic material.
> I guess an example would be if stygimoloch was described before
> pachycephalosaurus. If stygi
> turned out to be pachy, which name gets priority; the first named, or the
> adult morph.
Thankfully this is not the case (_Pachycephalosaurus_ was named first); but if
it was, then it would depend upon whether _Stygimoloch_ and
_Pachycephalosaurus_ shared the same species- or genus-level diagnostic
characters that could demonstrate that the two are conspecific or congeneric.
For establishing synonymy at the species level, a large sample would certainly
help (like the _Triceratops_ example mentioned by Mike Taylor). Uniting the
two at the genus level, however, is more a matter of personal taste.
Mike Taylor wrote:
> As I recall that talk, it made it pretty convincing case that
> Dracrorex and Stygiomoloch are juveniles, but didn't lay out case that
> what they're juveniles _of_ is Pachycephalosaurus.
Sounds similar to the _Nanotyrannus_/_Tyrannosaurus_ story. _Nanotyrannus_ is
certainly immature - but is it necessarily a young _T. rex_?
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