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Hi Jon, thanks for your thoughts on iguanodontian 
systematics (am ccing this to DML). 

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 
now I find it very hard to believe: the two species aren't just 
different in the features you state (hand and vertebral 
proportions, forelimb ratios, manual phalangeal counts, 
intersternal ossifications) but in others that seem less logical 
in terms of ontogeny. For example, they differ in number of 
caudal vertebrae (45 in _I. atherfieldensis_, over 50 in _I. 
bernissartensis_) and the shape of the quadrate (pillar-like 
in _I. bernissartensis_, curving in _I. atherfieldensis_). 

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. 
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_. 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. 
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. 

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 

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.

Much as I hate genera, hate generic proliferation, and 
thoroughly despise monotypic "higher" taxa, my vote is for 

Hmm, well it's by no means clear that Mantell's teeth were 
from _I. atherfieldensis_, so this might not be so cool:)

Darren Naish
School of Earth & Environmental Sciences
University of Portsmouth UK, PO1 3QL

email: darren.naish@port.ac.uk
tel: 023 92846045