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Re: Long-necked stegosaur, head tail mimicry?
Mike Taylor wrote:
> I should think so! It would be disastrous to
> resurrect that name to
> denote a completely different clade from the one that it
> has been universally understood to mean.
Mike, I disagree completely and utterly with you here. Now that I've gotten
that out of the way, here's why...
I don't think it's important in this case to permanently link the name
Euhelopodidae to what it *used to* include? If _Euhelopus_ is demonstrated to
form a clade with one or more other taxa (such as _Erketu_), then why not
apply the name Euhelopodidae to this clade? The name is available, after all.
Further, AFAIK the name Euhelopodidae has never been phylogenetically defined,
so it's a clean slate (phylogenetically speaking).
As for what Euhelopodidae was "universally understood to mean"... I disagree
here too. I don't think Euhelopodidae sensu Upchurch really is "universally
understood to mean" a clade containing _Mamenchisaurus_, _Omeisaurus_ and
_Euhelopus_ at all. This concept only came about fairly recently (c.1995), and
was not accepted by everyone. Upchurch himself later abandoned his own
Euhelopodidae, less than 10 years after. Euhelopodidae sensu Upchurch also
differs slightly from Romer's original composition of the group (as
Euhelopodinae), which also included _Tienshanosaurus_ and _Chiayusaurus_.
Changes in the composition of other venerable groups happen all the time. For
example, Spinosauridae once included all tall-spined theropods, such as
_Acrocanthosaurus_, _Altispinax_ and _Metriacanthosaurus_. These taxa are no
longer in the Spinosauridae, which now includes a whole new raft of taxa -
_Baryonyx_, _Suchomimus_, _Irritator_, and the like (as well as _Spinosaurus_
of course). Both Ceratosauria and Ceratosauridae have also gone through
convulsions in content, with the inclusion of _Ceratosaurus_ being the only
If you want to look at sauropods, then what about Cetiosauridae, which for most
of its history was a dumping ground for "primitive" or poorly known Jurassic
sauropods. But this nomenclatural history shouldn't preclude Cetiosauridae
from being phylogenetically defined to include _Cetiosaurus_ and its closest
relatives - as it was in fact used by Upchurch et al. (2004).
In summary, the fact that suprageneric groups can undergo significant changes
in content shouldn't mean that we abandon a name every time there is such a
change in content. If a new Euhelopodidae excludes taxa like _Omeisaurus_ and
_Mamenchisaurus_, but includes _Erketu_, then so be it. It just underscores
how our perception of _Euhelopus_'s relationships has changed.
> By the way, note the (rather poor) phylogenetic definition
> of Mamenchisauridae in Naish and Martill (2007:498) --
> Mamenchisauridae Young & Chao, 1972, a clade that we here
> diagnose as all those sauropods closer to Mamenchisaurus
> constructus Young, 1954 than to Saltasaurus loricatus
> Bonaparte & Powell, 1980 ...
Yes, the definition could be improved (amended) by the addition of further
external/negative specifiers. But apart from that, it seems fine to me.
> At least FOUR times -- in Mamenchisauridae, Diplodocidae
> (the neck of
> Supersaurus is best estimated at 15m, longer than any
> Brachiosauridae sensu stricto and once or more within the
> ill-defined cloud that is Titanosauria.
True. But I was referring specifically to the anatomical trait of increasing
neck length by wholesale recruitment of dorsals into the cervical column. As
you know, diplodocids and brachiosaurids lengthen the neck principally by
elongation of pre-existing cervicals. _Euhelopus_ and mamenchisaurids go one
better, and add extra vertebrae into the neck, at the expense of the anterior
dorsals. The stegosaur _Miragaia_ does this too - which incidentally is how
this thread originally started.