Re: Ceratopsian mass estimates

[Phil Bigelow <bigelowp@juno.com>]

Although I prefer the Paulian illustrations of T. rex to other artists'
illustrations, I have often wondered if Greg's calculated mass estimate
for a healthy T. rex is closer to the actual mass of a dehydrated T. rex
corpse.  Perhaps there is a certain "gestalt" factor involved in such
estimations (R.M. Alexander's equation aside).

I like the suggestion that Alexander's equation needs to be customized
for each taxon under study. Triceratops is no exception (but where do we
find an extant ornithiscian for a truth check??).

<pb>
--


On Wed, 20 Apr 2005 17:03:13 -0400 "Andrew A. Farke"
<andyfarke@hotmail.com> writes:
> > 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
> 
>