[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Dinosaur mass table online
Tim Williams <email@example.com> wrote:
>> The super titanosaurs were more like 30 m, and they had long whip
>> tails. Super mamenchisaurs reached 35 m, the length of the newly
> >mounted skeleton -- it's one big pappa.
>Be that as it may, I was using the available literature as a guide. Here,
>mamenchisaurs have been explicitly described as very slender sauropods. For
>>example, in the original description of _Mamenchisaurus sinocanadorum_,
>Russell and Zheng (1993) write:
> "_Mamnechisaurus_ was probably not as ponderously built as were
> _Brachiosaurus_ and _Apatosaurus_... because so much of its length
> consisted of an extremely long and light neck.... The proportions
>of the distal portion of the femoral shaft associated with the type
>skeleton of _M. hochuanensis_... are consistent with a body weight
>similar to that of _Diplodocus_."
>Now, I'm not denying that the mounted mamenchisaur skeleton you're referring
>to is "one big pappa". But to suggest that it was an exceptionally heavily
>>built sauropod that could have weighed 75 tonnes in life goes against
>everything that has been said previously about mamenchisaurs. Again, I'm not
>>saying you're wrong, but it's an extraordinary claim. At the very least,
>this "big pappa" sounds very un-mamenchisaur-like.
Except, of course, when _M. sinocanadorum_ was published, mamenchisaurs were
thought to be closely related with diplodocoids and now, they aren't, but are
thought to be basal eusauropods (the _M. sinocanadorum_ paper was published
1993, whereas a non-diplodocoid, data-set-based classification was first given
by P. Upchurch in 1995, as far as I know). As GSP said, mamenchisaurs
(including, presumably, _M. sinocanadorum_), have proportionately small limbs
compared to diplodocids (just look at his skeletal of (presumably) _M.
hochuanensis_ in the Scientific American book of Dinosaurs). So, going off the
femoral shafts may be misleading if not totally misguided. It is for this
reason that allometric limb-based mathematical formulas are not likely to give
accurate mass estimates in sauropods, in my opinion.
It is still peculiar, in my opinion, that a fat-bodied (and wide-hipped)
titanosaur in the range of 25-27 meters (my estimate) like _Argentinosaurus_
would still weigh that much less (about a fourth less) than a mamenchisaur like
_M. sinocanadorum_ that is 35 meters in length, which apparently are
"thinner-bodied" than titanosaurs (although, unfortunately, I have not seen a
multi-view skeletal of _Mamenchisaurus_, so it is hard to judge from mounted
skeletons which are notorious for not always being accurate--so maybe
mamenchisaurs were wide-bodied (?)). The only thing that I can think that can
account for this apparent difference is that titanosaurs have 10,
anteroposteriorly shortened dorsals (judging from _Malawisaurus_,
_Trigonosaurus_, and _Futalognkosaurus_), versus mamenchisaurs which have 12
dorsals that do not appear (to me) to be anteroposteriorly shortened much.
Combining the fact that _Argentinosaurus_ may be anywhere from 5-10 meters
in overall length than _Mamenchisaurus sinocandadorum_, and that titanosaurs
appear to have a short dorsal column may account for the (unexpected)
differences in mass estimates.
Of course, one could question how accurate the dimensions of the 35 meter mount
are for _Mamenchisaurus_, as the current full skeletal mount for
_Argentinosaurus_ is said to be 37 meters long, but _Argentinosaurus_ was
actually probably ~10 meters shorter (about 27 meters in my estimate; based
largely from scaling up from _Malawisaurus_). If _M. sinocanadorum_ is based
off fairly incomplete material (I don't know, as I don't have the paper
(hint,hint to anybody generous enough to share)), and *if* accurate
measurements of the material have not been published (again, I don't know),
than all these estimates based off the mount could be off; although by how
much, we don't know.