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Re: Sauropod necks (Re: DinoMorph Strikes Back!... or does it?)



Overall, as David said a very interesting and enlightening rant. Guess
we can scrap DinoMorph's conclusions for the most part.

> Basically every sauropod Kent has restored has an essentially straight neck
> and dorsal series, with if anything a hang-dog droop. [SNIP!] It's not
> impossible, but it's really odd.

One counter-example to DinoMorph, to use extant creatures, would be
the differences in common neck posture between the antelopes,
Alcelaphus and Connochaetes, hartebeest and wildebeest respectively,
which, coincidentaly enough are in the same subfamily. While I think
the range of movement is much the same wildebeest seem to favour a
more low swung head unlike other alcelaphines.  See
http://en.wikipedia.org/wiki/Alcelaphinae for the range.

> ZYGAPOPHYSES
> In all cases taut joint capsules prevent further sliding,
> so even barely overlapping zygapophyses don't disarticulate.

I hear that pleurodiran turtles really disarticulate their
zygapophyses when recoiling their neck at some perceived danger. Most
likely not appliable to sauropods but still, one more pebble in the
gears.

> For you see, when actually articulated in its NOA the cervical series of 3018
> takes a dive like a U-boat caught in the searchlight of a B-24 Liberator
> about to drop aerial depth charges on it. The neck, especially anteriorly, 
> follows
> such a strong inverted U-curve that the anterior end points straight down,
> and the head is literally below ground level. The neck articulated by Kent 
> will
> do this if the 4 disarticulated centra are pulled together so the balls fit
> fully in the socket. Which makes me wonder.
> Diplodocids were adapted for adapting a tripodal, static
> feeding pose like giant slothes. No need for the neck to be able to elevate
> strongly dorsally when the dorsal series is already subvertical, but being 
> able to
> reach forward of the erect body would be greatly expand the feeding range
> without having to go to the trouble of shifting position.  The ability to 
> ventrally
> extend the neck so far forced the articulations to be biased in favor of that
> posture. Carrying the head above the ground when on all fours therefore
> required most or all articulations to be significantly dorso-flexed. And that 
> is
> not a problem since the joints remain within normal articulation range.

And that pretty much nails the case shut in my view. Unless there's
something I'm unaware of :-/

> DICRAEOSAURUS

> What we can say is that the notion that dicraeosaurs walked about the
> Tendaguru landscape with their noses scrapping the ground as Kent shows just 
> because
> that's when the centra are flat on violates common-sense. What large herbivore
> does that? Every once is awhile one has to do what is logical - and get the
> head up.

Hmm... What was the paleo-environment like at Tendaguru? If there were
such things as fern meadows to graze having one's snout near ground
level would be a good position methinks. Not that I think the neck
posture was that most of the time ;-)


> MAMENCHISAURUS
> To look at it
> another way, if each cervical and anterior dorsal is dorsally elevated just 5
> degrees that's 95 degrees of total rotation. Again no evidence this was not 
> possible
> in life, it does not overflex the zygapophyses.

On a documentary I saw some years ago it was purported that Mamenchi'
couldn't rise its neck much above shoulder level because the
overlapping cervical ribs would basically prevent it as they braced
the neck skeleton in an horizontal position. I do see that your point
on the gentle curving of the neck yielding a high standing head and I
do know bone is flexible.
In the end they showed a CGI of Mamenchi' on an arid landscape
surrounded by shoulder high bennetitales stating that it was its
natural environment and that feeding exclusively on the plants had
specialized its neck structure.

> What is really interesting. or peculiar, about M. youngi as found is that the
> tail is strongly dorso-flexed. In the skeletal mount the tail base is
> "corrected" so that it is straight. And all the zygapophyses are pulled way 
> apart.
> You might think a certain someone had a hand in that. Seriously, when I
> articulated those beautifully preserved suckers I had no choice but to 
> position them
> in exactly the same position as in the quarry. So the death pose is the life
> pose, with the tail pitched up at a sharp angle, an exaggeration of the slight
> upwards arc of most sauropod tails. Probably a display thing.  As an artist I
> don't like it, looks dorky. Too bad.

The female Mamenchisaurus wouldn't think so. The loftier the tail, the
better ;-)
In fact this intrigues me deeply; I'd even like to see a skeletal
drawing or an illustration of that posture. Still I have the
impression, at least in diplodocoids, that the long tail served to
conterbalance the neck's weight thru' dorsal tendons on double-beamed
dorsal vertebrae. I believe this was not the case for Mamenchisaurus
as it had high neural arches on the anterior dorsals, though, since
the tail was that elevated couldn't it then have served as an
anchoring point?

> BRACHIOSAURUS

> Imagine long
> necked, 10-100 tonne beasts having nothing in their neck design to prevent 
> them
> from easily raising their heads too far above heart level – just a couple of
> meters according to the inadequate pressure hypothesis - misjudging when their
> little brains will run out of oxygen, getting whoozy and occasionally keeling
> over, only recovering and getting up - if not seriously injured - when cranial
> blood flow is restored. [SNIP!] . Probably via oversized hearts producing high
> BPs. Sorry all you cardio-pessimists. Of course long necked sauropods
> definitely were often feeding high in the crowns of trees, which makes a good 
> deal of
> sense for long necked herbivores when you think about it. It is interesting
> that no sauropod is known to have been able to be able to elevate the head
> higher than about 15 m. That is probably the height limit of land animals,
> probably set by the hydrostatic pressure in the feet.

Even I get whoozy when I get up too quickly from a sitting position.
Maybe sauropods had something similar to a giraffe neck's rete
mirabile or as someone put it in a post a year or so ago minding
sauropod respiration, the fleshy nasal cavity was coopted for that
work serving as a blood pool, which in my view that supplied the brain
when the heart couldn't make it.
That mention of feet hydrostatic pressure reminds me that we ourselves
have a sort of heart in the soles of our feet. No, I'm not talking
reflexology. The arterial blood pools in an extensive plantar vessel
net which is then pumped up the legs as we go about walking. It'd be a
possibility that sauropods had a similar strategy to help their hearts
do the job.

Renato Santos

--
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http://dracontes.deviantart.com/
http://drakontes.deviantart.com/
http://dracontes.sheezyart.com/
http://elfwood.lysator.liu.se/art/d/r/dracontes/dracontes.html
http://www.side7.com/art/dracontes/gallery.html
If you didn't get it by now, the subliminal order is "Go see" *does
queer gestures with hands*