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Re: Dinosaur mass table online






 Tim Williams <tijawi@yahoo.com> wrote:

>>GSP1954@aol.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 
shorter
 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.

Best regards,

Zach