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RE: Ceratopsian mass estimates



> Thomas R. Holtz, Jr.
> > From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> > Andrew A. Farke
> > Triceratops, USNM 4842, 10208 kg, 22505 lbs.
> 
> Damn!!
> 
> That doesn't seem right to me, at least if this is is anything like the
> size of the Hatcher mount at the Smithsonian. Comparing that
> animal to Stan (which faces off against it in the display), I would have
> guessed you are dealing with comparably massive animals
> (the T. rex has greater volume with that long tail and legs, but is filled
> with air sacs). Also, it doesn't seem right that those
> values are so much greater than what are at least grossly similar sized
> mammals (Elephas, Loxodonta).

Exactly. Note too that the values for "Kelsey" (the Triceratops at the
Indianapolis Children's Museum) are closer to what they "should be." At the
same time. . .USNM 4842 *is* one of the "beefiest" Triceratops out there.
Its circumference is a full 25% larger than Kelsey, and the bones are
absolutely beefy next to those of say, the "Raymond" specimen in Tokyo. Flat
out, it's a big specimen. I doubt that it's 10 tonnes of big, but perhaps
Greg's estimate was a little low, too?

> To me Greg's estimates are more reasonable, but it would be nice to see
> *where* or *why* you might be getting an overestimate.

Exactly--I am "happier" with Greg's estimates, too. My suspicion is that the
circumference/body mass equation isn't all that universal, and that it's
consistently overestimating. They've found the same thing for the M1/body
mass regression for mammals--i.e., every clade needs its own regression for
the estimates to be worth anything.

Also, I'll again point out that I'm not working from direct circumferences,
but from estimated circumferences. This also may be bumping up my estimates.
We've got an estimate based on an estimate!

And, an important thing to keep in mind is that almost nobody states which
specimens their Triceratops mass estimates are based upon. There is a *big*
size difference between, say, YPM 1821 and USNM 4842. I notice odd things in
some published estimates, too. For instance, I'm not sure how Seebacher
combined the USNM specimen with the BSP specimen to get a Triceratops that
weighed 5 tonnes (the two specimens are wildly different in body size).

At any rate, this body mass thing is an issue totally away from anything I'm
working on right now. Any students looking for a project? ;-)

Andy