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Re: Largest Dinosaurs



AAAAM49@aol.com wrote-

> What are currently regarded as the largest sauropods?  I know
Argentinosaurus
> and  Parailtitan were a few years back.  Are they still considered the two
> largest or have there been recent finds that were larger?

Calculating length for taxa based on a few elements is tricky enough,
especially in the case of sauropods, where tail length is nearly always
unknown.  Most of the largest sauropod taxa were titanosaurs, whose body
proportions are particularily poorly known.  However, based on recent
reconstructions of Saltasaurus, Opisthocoelicauidia and Rapetosaurus, I
estimated Argentinosaurus was ~22-26 m and Paralititan was ~20-24 m
(http://dml.cmnh.org/2001Sep/msg00402.html).  This is assuming the fibula
and humerus, respectively, scale isometrically and identically to the more
completely known taxa.  There are only a few sauropods with elements
reported of comparable size.  An undescribed femur from Morocco (Russell and
Taquet, 1999) is 2.36 m, Bruhathkayosaurus' tibia is 2 m, and Amphicoelias'
dorsal vertebra is huge.  Assuming Bruhathkayosaurus is a titanosaur and has
an isometrically scaled tibia, we get ~28-34 meters for the taxon.  The
Moroccan specimen might be ~28 meters long, using Patagosaurus as a
comparison (as a relatively conservative basal sauropod).  But since we have
no idea what kind of sauropod it is, its length could vary quite a lot from
this estimate.  Paul estimated Amphicoelias might be ~56-62 m long (I think
that was his estimate, and not mine, but my copy of his article is buried),
based on comparisons to smaller specimens, and more complete diplodocids.
No other known sauropod approaches this in length, even if the Moroccan
femur were scaled to a diplodocid body.  So I would say Amphicoelias is the
unequivocal longest sauropod, though its exact length is a matter of some
question.

If you think length is difficult to estimate, you should try mass
estimations.  Even small changes in length can cause large changes in mass,
since the latter increases with the cube of the former.  Mazzetta et al.
(2004) used numerous variables to estimate the mass of Argentinosaurus, at
73 tons.  Yet this is after a number of calculations that individually led
to estimates ranging from 60-88 tons.  They also estimated the length of
Antarctosaurus? giganteus based on individual calculations for A.
wichmannianus, which resulted in an average of 69 tons.  However, note this
doesn't scale isometrically to Argentinosaurus when femoral lengths are
used, as A? giganteus is heavier than expected for an Argentinosaurus with
the same femoral length.  So A? giganteus was apparently comparatively
bulkier than Argentinosaurus, and similar differences could easily affect
mass estimates for other titanosaurs.  If Bruhathkayosaurus is scaled
isometrically, using Argentinosaurus' fibular length, it results in a mass
of ~157 tons.  Scaling from A? giganteus' would result in a greater mass.
Of course, the length of Bruhathkayosaurus' tibia has only been roughly
reported, so any small variations from its supposed 2 meter length would
cause differing mass estimates as well.  You can picture the uncertainties
involved in estimating the mass of the Moroccan sauropod.  Paul estimated
Amphicoelias at 125-170 tons, so it's anyone's guess whether it or
Bruhathkayosaurus was larger.

We both know the big Amphicoelias specimen was lost, so all we have is a
drawing.
The situation for Bruhathkayosaurus is only slightly better.  The
description and illustrations are TERRIBLE, and the association of elements
isn't certain at all.  Chatterjee (pers. comm.) says it's titanosaurian
based on comparisons to Lameta titanosaurs, and rejects a theropod
identification based on comparisons to Lameta abelisaurs.  But there have
been no particular details given that would support any taxonomic
assignment, though the tree trunk idea seems to exist simply because it was
rather large.  I can send a copy of the original description to those who
want to laugh at the drawings, and squint at the photographs in an attempt
to make out bones.

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html