[darren.naish@port.ac.uk: Giant brachiosaur & Rhynchocephalia]

[Mike Taylor <mike@indexdata.com>]

Forwarded on behalf of occasional HP Darren Naish.

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Date: Mon, 14 Feb 2005 07:48:57 +0000
From: "Darren Naish" <darren.naish@port.ac.uk>
To: mike@indexdata.com
Organization: University of Portsmouth
Subject: Giant brachiosaur & Rhynchocephalia

I'm being kept busy, to say the least, with _Eotyrannus_ 
right now but wanted to address two things that have come 
up on DML recently.

Firstly, regarding the size of the English brachiosaurid 
cervical vertebra MIWG.7306 (referred to affectionately by 
some of us as 'Angloposeidon'), Mike pointed out that the 
specimen is 745 mm long, not 1230 mm as suggested by 
David. I donÂt know where the 1230 mm came from, but in 
2002 I gave a few talks and published a few articles (e.g., 
the one in _Dino Press_ 7) where the total length was given 
as 1060 mm. While 745 mm is the officially 'correct' length 
(it is the maximum measurable centrum + condyle length), 
there's more than one way to measure a vertebra and one 
could argue that my 1060 mm is not incorrect. Initially (viz, 
before clever people told me otherwise) I stupidly thought 
that the total length of any vertebra meant, like, total length 
- - that is, maximum measurable length from tip of prezyg to 
rim of cotyle. Because the preserved right prezyg of 
MIWG.7306 is so long, _with_ its prezyg attached the total 
measurable length (from tip of prezyg to rim of cotyle) is 
1060 mm (I made the mistake in the paper of not illustrating 
the prezyg attached to the rest of the vertebra. Mathew 
Wedel made a good case during review that this should 
have been done: ultimately I didn't do it because [long 
story] the figures for this paper had already caused me 
MONTHS of grief). 

MIWG.7306 can therefore be described as over 1m long, so 
long as it's understood that this isn't the total length as 
measured by convention. And just to make it clear (it's 
pointed out in the paper, but it's worth saying it again), 
MIWG.7306 was fairly certainly not the longest cervical in 
the series. The animal was probably on par with 
_Brachiosaurus brancai_ in terms of neck length but, as 
Wedel et al. point out in the Acta Pal Pol paper with regard 
to _Sauroposeidon_, the problem as goes total length is that 
we can't be sure that the neck length : total length ratio was 
the same in these sauropods. _Sauroposeidon_ had a longer 
neck than _B. brancai_, for example, but does that mean that 
the whole animal was definitely bigger than _B. brancai_? 
Maybe/probably it was, but the possibility can't be excluded 
that _Sauroposeidon_ was the same size as or even smaller 
than _B. brancai_, but with a particularly long neck for its 
size. The same goes for the animal represented by 
MIWG.7306. The same size as _B. brancai_? Or bigger? Or 
smaller? A second vert, probably from the same individual 
as MIWG.7306, is known (IWCMS : 2003.28) and is 
smaller at 640 mm - but this is only the centrum length (the 
specimen is pretty battered and heavily eroded). There's no 
way of working out which vert it was.

Moving on 

I note there continues to be some uncertainty over current 
application of the term Rhynchocephalia Gunther, 1867. 
Originally coined just for _Sphenodon_ (prior to 1867 
regarded as an agamid), Rhynchocephalia is now well 
established in the herpetological literature as the name for 
_Gephyrosaurus bridensis_ + Sphenodontia (_G. bridensis_ 
is Evans, 1980; Sphenodontia is Williston, 1925 
[Sphenodontida is Estes, 1988]). This decision was first 
made by Gauthier et al. 1988 (prior to Whiteside's 1986 
work on _Diphydontosaurus_ it wasn't realised that _G. 
bridensis_ was close to sphenodontians). 

As has been noted previously, I think it's a little unfortunate 
that Rhynchocephalia has now become co-opted for this 
clade given that, during its history, this name has included 
so many disparate groups, all of which (rhynchosaurs, 
choristoderes, thalattosaurs, younginiforms, etc) have little 
to do with sphenodontians. Indeed Benton (1985) tried to 
get rid of the term 'since [it] has become too wide in 
application' (p. 147) and wrote that 'The group has clearly 
got completely out of hand, and the use of the name 
Rhynchocephalia for _Sphenodon_ and its relatives alone 
would be confusing' (p. 147). Personally I don't think 
Gauthier and certain of his colleagues make the best 
decisions when it comes to the naming of newly recognised 
clades: he/they have a nasty habit of using old names that, 
like Rhynchocephalia, come burdened with a history. Sauria 
and Pseudosuchia are other examples of this sort of thing. 
On the other hand, the _Gephyrosaurus_ + Sphenodontia 
clade needed a name, and sphenodontians are the only 
group that have always formed the 'core' of 
Rhynchocephalia.

Refs - -

Benton, M. J. 1985. Classification and phylogeny of the 
diapsid reptiles. _Zoological Journal of the Linnean 
Society_ 84, 97-164.

Gauthier, J., Estes, R. & de Queiroz, K. 1988. A 
phylogenetic analysis of Lepidosauromorpha. In Estes, R. & 
Pregill, G. (eds) _Phylogenetic Relationships of the Lizard 
Families_. Stanford University Press, pp. 15-98.

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

http://web.port.ac.uk/departments/sees/staff/NaishD.htm
email: darren.naish@port.ac.uk
tel: 023 92846045
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