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RE: Precision

As an addendum to Mike's response (which was right on the money), one extra caveat is that such estimates are based on individual specimens. Therefore, when we say...

"Brachiosaurus had an estimated body length of X m and an estimated mass of Y tonnes"

what we are really saying is ...

"The largest *known* specimen of Brachiosaurus had an estimated body length of X m and an estimated mass of Y tonnes".

'Maximum body size' in non-avian dinosaurs has its own set of caveats, especially if the work of Sander and Klein (2005) is any guide. This study found that maximum body size in _Plateosaurus engelhardti_ varied enormously from one individual to the next. Some had reached maximum size by age 12, while others were still growing at 26-27 years old. The smallest specimen was 4.8 m long when fully grown, whereas others attained a body length of around 10 m long (and still may not have 'topped out').

Extrapolating this beyond _Plateosaurus_, it may be that we have markedly underestimated just how 'big' (long/tall/heavy) many non-avian dinosaur species can get, especially if a given species is based on only one or a few specimens. On the other hand, the impressively large specimens on which the biggest sauropod taxa are based (_Argentinosaurus_, _Seismosaurus_, _Brachiosaurus_, etc) may actually be close to the maximum body size. Or they may not be. Most non-avian dinosaur species are not as helpful as _Plateosaurus_ in providing us with a large enough 'pool' of specimens for us to gauge variation in adult body size, and to get a 'feel' for how big they got.



From: Mike Taylor <mike@indexdata.com>
Reply-To: mike@indexdata.com
To: rahul721@hotmail.com
CC: dinosaur@usc.edu
Subject: Precision
Date: Mon, 27 Nov 2006 15:48:36 +0000

Rahul Daryanani writes:

 > Firstly, I'd like to thank all those who helped me out with my
 > questions on Bruhathkayosaurus, especially Mike and Mickey.
 > Secondly, yes, this article is concerning sizes too (this is
 > actually the thing I find most intersesting about dinosaurs). I'm
 > working on a book on the largest sauropods, and I'm going REALLY
 > crazy when it comes to sizes.
 > I'm not only talking about the ones where evidence is sparse. Take
 > Brachiosaurus. We have a complete skeleton, and as Mike noted in
 > one of his replies, estimates range from 15-180 tonnes. That's a
 > difference of more than 1000%. Seriously, considering B. brancia is
 > probably the best represented sauropod, that's more than
 > ridicoulous (no offense).

Actually, while _B. brancai_ is indeed very well represented, other
sauropods have much more and better material -- notably _Camarasaurus_
and _Shunosauris_, both known from multiple complete skeletons
including skulls.  Still, _B. b._ is certainly sufficiently well known
that estimating its mass ought to be a science rather than an art.

And because it's bigger, sexier and generally better(*) that _Cam_ or
_Shuno_, much more work has been done on its mass than that of its
lesser brethren.

(*) OK, "better" is an artistic rather than scientific judgement.

 > That's why everything I've read in books, articles, and on various
 > websites, has really got to me. For example, Gillete's book cited
 > Seismosaurus at a minimum of 120-150 feet long, and 100 tons. Other
 > books put it at over 170 feet and 150 tons. A couple of the newer
 > articles cite it at 110 feet and 25 tons. See what I mean? How is
 > it possible for all those writers and scientests to make such
 > precise estimates when evidence is so minimal.

You should have a pretty good handle on this by now.  There are all
sorts of factors at work here, including not only honest scientific
disagreement concerning life restoration, but also the different
results of different approaches to mass estimation; not to mention
uncertainty about, or misidentification of, remains.  And all of this
is potentially peppered with ego-inflation ("Half the discoveries in
dinosaur paleontology can be summed up as 'New Giant Dinosaur Proves
Paleontologist Has Largest Penis'" -- Nick Longrich.)

By the way, you've probably already seen
but if not then you may find it helpful.

 > A very good book called 'Supergiants: The Largest Dinosaurs', give
 > estimates from the scientests themselves, which I've discovered are
 > more or less unreliable themselves.

Yep!  :-)

 > That probably gives you the idea of what I mean. How is it possible
 > for anyone to cite estimates like these with such terrible
 > evidence.  Could someone help me out here?

No.  No-one can.  That's just the way it is, at least for now.  I
think that the problem is exacerbated by a lot of books -- and not
just kids' books -- giving unadorned masses for various dinosaurs with
no discussion at all of the uncertainty.  And because such books tend
to quote from each other rather than going back to the primary
literature, the problem doesn't get fixed, and estimates such as
Colbert's 78 tonnes become enshrined as Facts That Everyone Knows.

Now, then --

 > Otherwise, I'll leave my book on hold until more evidence is
 > discovered, or I'll use my own calculations (which are just as
 > unreliable, as I used better known genera like Diplodocus and
 > Brachiosaurus for comparisons, and the estimates vary just as
 > crazily for them, too).

Why not write up the problems?  Wouldn't that make a much better book?
Not just better science (as it'd be more honest) but more interesting,
too?  I think most kids would really enjoy seeing how dinosaur science
is done, and much disagreement there is.

_/|_ ___________________________________________________________________
/o ) \/ Mike Taylor <mike@indexdata.com> http://www.miketaylor.org.uk
)_v__/\ "Don't worry about people stealing your ideas. If your ideas
are any good, you'll have to ram them down people's throats" --
Howard Aiken.

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