Re: Gallery and Commentary for Copenhagen Mamenchisaurus

[Mike Taylor <mike@indexdata.com>]

> Date: Wed, 23 Jun 2004 13:47:43 -0400
> From: DinoBoyGraphics@aol.com
> 
> Matt is right that rearing as a habbitual feeding behavior has "yet
> to be demonstrated," but this doesn't make it any less likely than
> the hooverasaurus interpretation.

No indeed.  The problem is that as things stand, there is _no_
meaningful published evidence either for rearing _or_ hoovering.  They
are two equally unsupported hypotheses.

> It is far more expensive to have an insanely long neck your whole
> life than to simply take three steps any time you want to get to new
> ground fodder.

As I said in my previous message (did you not read the one here I
quoted Paul 1988 on this?) my own intuition agrees with yours here.
The problem is, it _is_ just intuition until someone comes up with
some actual numbers.  Paul gives numbers for the energetic cost of a
large animal moving, and the energetic value of fresh browse, but --
crucially -- no figure is given for the energetic cost of maintaining
respiratory dead-space (nor for the other metabolic costs associated
with maintaining this structure).  And of course it is this that needs
to be compared with locomotion cost: the energetic value of food is a
constant and thus irrelevant.  (This is why I was fishing for a copy
of the Daniels and Pratt paper -- I want to see if they put numbers on
these costs.)

> [...] which is why no grazing animals have really long necks today
> (that is, their necks are just long enough to reach the ground).

For what it's worth, I am not convinced that this is true.  There are
plenty of birds that have necks substantially longer than they need to
be to reach the ground.  But I don't think that really tells us
anything because the cost of an extra foot of ostrich neck is
negligible compared with the costs of an extra twenty feet of
_Mamenchisaurus_ neck.  Once again, we run into the problem that there
are no useful extant analogues for sauropods.

> What's more, while I cannot comment on Steven's SVPCA talk, his SVP
> talk had absolutely no dinomorph modeling of Brachiosaurus, instead
> it had Photoshop manipulations of Janesch illustrations; not exactly
> confidence-inspiring rigor.

:-)

To be fair to Stevens, his 2002 paper includes an unretouched
illustration from Janensch 1950 showing the cervico-dorsal region of
the SII _Brachiosaurus_ as discovered, which seems to suggest a
horizontal neck posture: Stevens, K.A. 2002. DinoMorph: Parametric
modeling of skeletal structures.  Senckenbergiana lethaea 82(1):23-34.

Speaking for myself, I find it very hard to believe in a
horizontal-necked _Brachiosaurus_, and it infuriates me that whatever
DinoMorph-based findings Stevens and Parrish have come up with are not
published (and therefore not refutable).  Still, though: at this stage
"I find it very hard to believe" is the strongest evidence I can come
up with; and even _I_ don't find that conclusive :-)

It was ex-HP Darren Naish who told me, if I'm remembering this right,
that S&P modelled _Brachiosaurus_ in DinoMorph and presented the
results at an SVPCA.  If Darren has anything to add on this (which may
just be "you've got it completely wrong"), I'll forward his response
to the list.

> I currently have two WDC Camarasaurus specimens with good necks, and
> they show clearly an upturned keystone-shaped centra in the
> cervico-dorsal region [...]

Interesting!  I would very much like to see photos of these if you
have them.  I've seen keystone-shaped centra asserted before, but
never yet actually seen one.  (Again, see Stevens 2002: this paper
contradicts Paul's claims of trapezoidal centra.)

The other thing about keystoned cervicals, of course, is that if they
do exist then they make it hard to _lower_ the neck, which is clearly
necessary for drinking.  So keystoning would ease the adoption of
elevated postures at the expense of making other postures more
difficult to adopt.  This is an adaptation that would only seem to
make sense in animals that kept their necks elevated for the great
majority of the time.

> I have not been able to check Brachiosaurus or Mamenchiosaurus, but
> if Steven's is wrong again (and I have no problem imagining such a
> situation at this point), then there is no Fundamental Sauropod
> Problem, because long-necked sauropods either reared or had upturned
> necks.

Which of these category do you place _Cetiosaurus_ in?  Martin 1987
seems to demonstrate that vertical flexion was limited, and that
animal does not look like it was built for rearing, in the way that
diplodocids may be.

> I am not claiming that this is "proven" or any such thing, but it's
> ridiculous to cite the anatomically "undemonstrated" nature of
> habitual rearing while ignoring the equal lack of demonstration (if
> not outright impossibility) of the engergetics of long-necked
> grazers.

I'm not ignoring anything.  I'm just waiting for someone to convince
me one way or the other.  Until that happens, I still perceive a
Fundamental Sauropod Problem.

> Rigor goes both ways

And here, at least, we are in complete agreement :-)

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