Re: Precision

[dinoboygraphics@aol.com]

Tim and Mike (and possibly others) "collaborated" to write the 
meta-post I'd like to comment on:

> > Certain estimates are less trustworthy - like Colbert's 78-tonne
> > uber-brachiosaur, for example.  It all depends upon the method(s)
> > used to estimate body mass, including the accuracy of the 3-D
> > ("flesh-and-blood") reconstructions.

> ... and indeed the accuracy of computer models.  Here I am thinking of
> Gunga et al's (1995) Colbert-like mass estimate of 74.4 tonnes, which
> is based on a computer model built out of tubular sections ... that's
> circular, rather than elliptical, in cross-section.  Using this method
> they managed to estimate 11 tonnes for the neck alone(!), i.e. three
> quarters of the mass that Russell et al. (1980) came up with for the
> whole animals.  So the moral is that more recent estimates, such as
> that of Gunga, are not necessarily better.

Agreed!  To further editorialize, mass estimates taken from say, 
femoral circumfrence simply are not very accurate, even amongst extant 
animals.  It may seem "less arbitrary", but it's more wrong none the 
less.  While volumetric mass estimates rather obviously depend on the 
accuracy of the model used, this isn't really a bad thing, it just 
means that we need to work to make our models as accurate as possible.  
Having spent some time dipping models (and calculating 3d scans volumes 
in a computer) I ahve to second Greg Paul's DInofest volume in that 
"artistic judgements", e.g. adding a dewlap, or making a limb more or 
less scrawny, don't have nearly as large of an impact on a models 
volume as simply getting the basic proportions wrong (e.g. making the 
trunk far too long, or not being able to fit a skeleton inside the 
model).  This does not mean that all of Greg's estimates should be 
taken as gospel (sorry Greg), but at the least they are good attempts 
based on actual anatomical interpretations.  If those interpretations 
are in error in some way (e.g. if the chest is too wide, as David has 
suggested) then we can fix those errors and get more precise.  The 
problem with mass estimates isn't that too many people have produced 
disperate estimates, it's that not enough people are trying with a more 
standardized method.

> Curtice and Stadtman (2001) made a pretty convincing case for the
> _Dystylosaurus_ specimen being an anterior dorsal of _Supersaurus_
> (not least because it was found between the two _S._ scapulae :-) but
> I noticed that Upchurch et al. (2004) still lists _D._ as a
> brachiosaurid, which was the assessment made by McIntosh (1990).
> I've not spoken to Paul about this, so I don't know whether this
> constitutes a disagreement with Curtice and Stadtman's assessment; but
> I think it's more likely that their manuscript was submitted before
> C&S's became available.

Dave Lovelace and myself are also supporting synonymizinf Dystylosaurus 
into Supersaurus.  Frankly, we think Curtice and Stadtman did a good 
job with that, but we went ahead an re-examined it; it's pretty clearly 
Supersaurus when, you know, you have more Supersaurus bones to compare 
it with.

> By the way, _Supersaurus_ is generally considered to
> be closest to _Barosaurus_, not _Diplodocus_ -- for good reasons I
> think.  I know there is another hypothesis out there, but that
> hypothesis doesn't bring _Supersaurus_ any closer to _Diplodocus_.

Indeed, this has traditionally been the case.  Almost entirely because 
of the caudal series (which we believe to actually be Barosaurus) that 
was ascribed to it by Curtice.  The tail attached to our Supersaurus 
(hurray for single taxon sites!) doesn't look remotely likely 
Diplodocus, and is also clearly not Barosaurus.  There are some other 
Morrison sauropods that it looks like though...


Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com


________________________________________________________________________
Check out the new AOL.  Most comprehensive set of free safety and 
security tools, free access to millions of high-quality videos from 
across the web, free AOL Mail and more.