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Fw: IGUANODON WARS [Attack of the Clades?]



Second try, since this message will probably get bounced by the list for an
"illegal attachment." I think I must be smoking crack today: I somehow
included a link to my web browser in the message... !!!!!!!!!!!!!!!!!!!!!!

> > Hi Jon, thanks for your thoughts on iguanodontian
> > systematics (am ccing this to DML).
>
>     Actually, this makes me a little grumpy, as my response was intended
to
> be FYEO. I am now placed in the uncomfortable position of conducting a
> discussion of an offhand comment in an unpublished paper in public, in
front
> of and involving the editor of the volume for which the paper was
intended.
> I cannot stress to the list enough the importance of CHECKING TO SEE IF IT
> IS OK WITH ALL PARTIES BEFORE BRINGING PRIVATE DISCUSSIONS INTO PUBLIC.
Any
> grouchy comments below can be traced to this issue. I tried to edit them
all
> out, Darren... sorry. :)
>
>
> > Re: your suggestion that _I. atherfieldensis_ and _I.
> > bernissartensis_ might be growth phases of the same
> > species, this is interesting and thanks for the data but right
>
>     Not what I said. The gist of the passage I relayed was that, given the
> range of variation we observed in hadrosaurs, the two morphotypes of
> Iguanodon would be considered the same species. There appears to be
> substantial anisometry with respect to size in I. bernissartensis; "I.
> atherfieldensis" specimens plot where the Iguanodon trend intersects the
> hadrosaur trend. The ultimate point being that you need to be careful in
> coding OTUs lest you bias your study with morphologically immature
> specimens. There certainly is a strong *implication* in this discussion
that
> the two forms may be conspecific, but I feel that such a determination is
> beyond the scope of our analysis and requires a close look at the actual
> material.
>
>     To clarify against the almost inevitable (on the Dino List, anyway)
> interpretation: I am not criticizing any aspect of Norman's work. I hold
it
> in the highest regard, and I have used it as an example of the level of
> scholarship I believe is worth striving for.
>
>
> > now I find it very hard to believe: the two species aren't just
> > different in the features you state [...] but in others that seem less
> logical
> > in terms of ontogeny.
>
>     Having considered the subject in a little depth, I am currently quite
> uncertain regarding what (if anything) is logical about ornithopod
ontogeny,
> beyond the general observation that "things get bigger." There seems to be
a
> good amount of individual variation within what we believe to be species,
> and that could heavily overprint any ontogenetic pattern. There is
certainly
> variation in the pattern of the ontogeny of vertebrates itself, such as in
> the ossification sequence of carpal elements in tapirs (Matt Colbert, in
> prep.) and attainment of characteristics of osteological maturity in
> crocodylians (Brochu's paper). I'm very interested in how we should
approach
> this issue in the fossil record.
>
>
> > For example, they differ in number of
> > caudal vertebrae (45 in _I. atherfieldensis_, over 50 in _I.
> > bernissartensis_)
>
>     Quoting Norman (1980, p. 42, emphasis mine), "Several of the specimens
> from Bernissart possess ALMOST complete articulated tails... In one of the
> more complete specimens (IRSNB 1726) the tail, as preserved, comprises
> forty-six articulated vertebrae. It seems unlikely there were many more
than
> this in the tail of _I. bernissartensis_, and fifty would seem a
reasonable
> estimate..." And, Norman (1986; p. 310), "The remainder of the tail
(34-?45)
> is not preserved in any specimen." I therefore do not find your point
> particularly compelling, based on the evidence as I read it.
>     On the other hand: anotomical authorities I have consulted have
> communicated their expectation that caudal vertebrae will vary both
> individually and ontogenetically. I am afraid I have been unable to find
the
> expected numerous supporting references concerning variation in caudal
> vertebral count in the literature. I also can't cite much in the way of
data
> from other ornithopods, thanks to their notorious habit of not preserving
> complete tails. In the ornithopod literature, Gilmore (1946) expresses his
> expectation that caudal count will vary both individually and
> ontogenetically in reptiles. I won't feel comfortable until I find more
> concrete references, but I am discomforted by the notion than you
apparently
> are.
>
>
> > and the shape of the quadrate (pillar-like
> > in _I. bernissartensis_, curving in _I. atherfieldensis_).
>
>     This has been a sticking point for me for a number of years. Recently,
I
> have been made aware of authorities who plan to synonymize certain
> ornithopod taxa that differ in the degree of curvature of their quadrate,
> and I am myself coming to the conclusion that there may be unrecognized
> problems with this character. I also have some doubts that the difference
in
> Iguanodon is as pronounced as it appears at first. The caudal margin of
the
> bone, where I think curvature is best appreciated, does not appear to
differ
> as much as the rostral margin in these morphotypes as restored by Norman
> (1980; 1986). The rostral margin, where the difference appears more
> pronounced, varies in thickness somewhat among apparent conspecific
> hadrosaurs, especially above the quadratojugal articulation. My hunch is
> that at least some of this is due to slight differences in the position of
> the element relative to the rest of the skull, but it is certainly
possible
> that there is true variation as well. This is something I actually plan to
> look at in detail for hadrosaurs some day. It would be truly marvelous to
> get a chance to examine Iguanodon in detail as well. Hopefully the
specimen
> HP Carpenter refers to will shed some light on this.
>
>
> > Also, it would be nice to have the figures for this but surely
> > there are some _I. atherfieldensis_ individuals that overlap
> > in size with some _I. bernissartensis_ individuals, plus there
> > are (to my knowledge) no specimens that are intermediate.
>
>     Doesn't bother me in the least. It  is not my contention that "I.
> atherfieldensis" is necessarily either A) a "dimorph" or B) an ontogenetic
> stage of  I. bernissartensis. In at least some features, Ia falls on the
> hadrosaur growth curve as well. My point was that, from what little data
are
> available, they appear to fall on the same growth curve. The truth could
be
> neither A nor B, it could well be both. Since I have not been able to
> conduct a proper study of the material, it would not be proper for me to
> express an definite opinion on this matter.
>     Entering the realm of speculation, a continuous pattern of
morphological
> variation is suggested by the data in some cases of "sexual dimorphism"
> among dinosaurs (e.g., Protoceratops, Chasmosaurinae). It is certainly
> possible that specimens of Iguanodon "atherfieldensis" are those few
> individuals in the species that represent the extremes of more than one
> morphological continuum (e.g., the most "gracile" and the most
"feminine"),
> with juveniles resembling the endmembers of one or both of these
> morphoclines. Exploration and documentation of this sort of pattern of
> variation is actually a long-term research goal of mine. Anyway, right now
> all this amounts to speculative crap, but I thought I'd bring it up just
to
> suggest that there need not be just one morphocline in a species, and that
> the distribution of morphotypes need not superficially be bimodal, highly
> kurtotic, or unskewed.
>
>
> > Sorry to pull in anecdotal evidence, but fragmentary bits
> > (MIWG/IWCMS metatarsi) indicate there also seem to be
> > gracile _I. atherfieldensis_ that reached the size of a big _I.
> > bernissartensis_.
>
>     Anecdotal evidence is ok. I wonder, however, what apomorphies are
> present in the metatarsus of Iguanodon that allow this referral? I don't
> recall any myself. Anyway, what few data I have suggest variation in the
> proportions of the metatarsals among hadrosaur specimens believed to be
> conspecific, especially in metatarsals II and IV. Some of this variation
> appears to be as extreme as that observed in Iguanodon. We really need
more
> data on this, though.
>
>
> > It also seems unlikely to me that the
> > diagnostic dorsoventrally deep plate-like prepubic proc. of
> > the pubis in _I. atherfieldensis_ could ontogenize (new
> > word) into the shallower, more prong-like process of _I.
>
>     If you'll recall the passage I sent you, the suggestion was that this
> may be individual variation, not neccessarily ontogenetic variation. The
> argument is that a level of variation *nearly* equivalent to this is seen
in
> some hadrosaurs, and the incompleteness of the marginal bone in the
elements
> from Bernissart indicates that the full dimensions of some of the compared
> elements are not preserved (indicated by Norman's illustrations). However,
> this remains an issue I am not entirely comfortable with. Certainly, such
> differences in hadrosaurs are often associated with taxonomic boundaries.
> Interestingly, although the prepubis is absolutely deeper in Ia, the ratio
> of neck to blade depth (which is pretty consistent wihtin putative
hadrosaur
> species, and appears to be systematically informative) is similar in the
two
> species. I don't know what to do with that, we need more data. It is
> possible that overall pubis depth varies at the species level generally.
>
>
> > bernissartensis_. However, I see that your theory is a new
> > idea based on your work on hadrosaurs: hopefully this will
> > prompt someone in future to look into it in more depth.
>     If someone has $15,000 to donate and a pair of ginormous callipers,
I'll
> ahppily go and do it myself!
>
>
> > Incidentally, one should not talk of 'crown' hadrosaurs
> > seeing as, by definition, crown groups only encompass
> > extant representatives of clades. A common error (the most
> > notorious of which might be Sullivan's 'crown-group
> > Ankylosauridae').
>
>     We address this explicitly earlier in the paper; sorry I didn't send
> that bit. Using "stem" and "crown" avoids the somewhat contentuous issue
of
> where on the tree the term Hadrosauridae should be applied. I favor a very
> strict definition (as do certain noteable ornithischian specialists).
> However, since others have argued strenuously (if not effectively) to
> include their favorite "basal" hadrosaurs in the definition, we opted to
> avoid this issue by picking a very broad definition of Hadrosauria (so
that
> most everything of interest is a "hadrosaur"), and dodged the issue of the
> "family" definition altogether. Since the "crown" term is being used
> (inappropriately) in some circles, and it proceedurally amount to the
> concept we wanted, the group of well-known, well-characterized,
unequivocal
> members of an established taxon (for taxa with extant members, this is the
> true crown), we felt it was better than adopting a new term for a clade
that
> already suffers from nomenclatural proliferation.
>
>
> > ---------------------
> > Actually, I. atherfieldensis comes out closer to haddies...
> > just as juvenile chimps might code closer to humans in a
> > morphological analysis.
> > ---------------------
> > They probably wouldn't seeing as the _Homo_-like
> > characters of baby chimps (proportionally larger cranium,
> > smooth brow ridges, flatter face) are not seen in hominins
> > closer to _Homo_ than to _Pan_. Baby chimps instead have
> > the intermembral indeces, palatal shape, long dentary
> > symphysis, dorsoventrally long ilia, opposable hallux and
> > laterally round (rather than oval) femoral condyles of non-
> > hominin hominids so surely would group close to _Pan_
> > even if coded as a separate OTU.
>
>     Certainly a good point, from what I understand of hominid systematics.
> My comment was an off-the-cuff comparison regarding the dangers of coding
> different ontogenetic stages in an analysis. Since I (obviously) don't
know
> anything about hominid morphology, perhaps you would enlighten the group
on
> some of these characters... I was under the distinct impression (from
> childhood trips to the zoo) that an opposable hallux was ancestral for the
> great apes. Is this, and the other characters, really a synapomorphy of
> _Pan_? It sounds, from your description, like the characters you listed
are
> plesiomorphies, and therefore would not result in a _Pan_ + juvie _Pan_
> clade in the analysis. You should then have a trichotomy of _Pan_,
juvenile
> _Pan_, and Homininae, which might, with poor sampling of the latter taxon,
> result in selection of a different ingroup tree for hominines, and
different
> interpretations of the ancestral states. Which was where I was going in
the
> first place.
>     Obviously, the tenor of the above is a bit of a combative, grouchy
> response to a nitpicky point (such picking of nits from HP Naish is always
> good-natured and well-informed and therefore very welcome). I would not be
> suprised to be told there are apomorphies of _Pan_ that develop relatively
> early in ontogeny. These would probably be recognized as such by
specialists
> and would be applied to the problem, resolving the issue nicely.
>     As far as I can tell, Hominids are a realtively well-sampled and
> well-understood group (by paleontological standards). The "viscinity" of
> Iguanodon on the ornithopod tree is, judging by the recent pronounced
> increase in named taxa, probably relatively poorly sampled and poorly
> understood (from uncertainty in recent analyses, including my own, and
from
> this very discussion). Coding a morphologically immature specimen might be
> especially misleading under these circumstances. That's all.
>
>
> > ---------------------
> > Much as I hate genera, hate generic proliferation, and
> > thoroughly despise monotypic "higher" taxa, my vote is for
> > _Mantellodon_.
> > ---------------------
> >
> > Hmm, well it's by no means clear that Mantell's teeth were
> > from _I. atherfieldensis_, so this might not be so cool:)
>
>     The idea was just to give the man SOME credit in the name of a valid
> taxon. Normansgiantbitchincoolmonographosaurus is a bit long, and hardly
> "euphonious." ;)
>
> Wagner
>
>
> REFS:
>
> Gilmore, C. W. 1946. Notes on recently mounted fossil skeletons in the
> United States National Museum. Proceedings of the U.S. National Museum,
> 96(3196):201-203.
>
> Norman, D. B. 1980. On the ornithischian dinosaur Iguanodon
bernissartensis
> of Bernissart (Belgium). Memoires de l'Institut Royal des Sciences
> Naturelles de Belgique, 178:1-103.
>
> Norman, D. B. 1986. On the anatomy of Iguanodon atherfieldensis
> (Ornithischia: Ornithopoda). Bulletin de l'Institut Royal des Sciences
> Naturelles de Belgique. Sciences de la Terre, 56:281-372.
>