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Sauropod rearing (was Sauropod Energetics (Peristaltic pump))



I heartily welcome Kent's suggestion that we engage in what would constitute evidence for sauropod rearing or lack thereof. I hope to contribute to this myself when I get back to Wyoming, but I did want to point out an issue I have with the analogy regarding neurological control:

"[Regarding the vestibular coordination issue, ever walk while carrying an extended extension ladder vertically, like when you are painting a house, and you want to move the ladder around the corner? As the upper end of the ladder sways about its up to you to correct it before its too late. In this case you're on the ground looking up, and you've got a big clever head on your shoulders. In the sauropod's case, its itty bitty head is way up there, trying to reach something to eat while suspended at the end of a dynamically flexing neck that's extended above a swaying trunk supported by perhaps somewhat wobbly legs on uneven ground, and it's got to decide in real time whether the current degree of swaying that feels and sees is within tolerance, or whether its time to take a sidestep, or ...] "

I think this analogy has several flaws; first of all, the cleverness of my head (well, ok, pick YOUR favorite example...) is really irrelevant to the issue of basic neurological control. It is not at all clear that EQ has the slightest correlation with basic neuromuscular control; idiotic fish and snakes are perfectly graceful, while teenage humans can be hopeless. In all seriousness, can anyone cite a single paper that correlates high EQ (which tends to be associated with behavior flexibility and the ability to learn new responses to novel situations) with locomotor adeptness? If not, let's please end this pernicious myth.

While working on our (poorly articulated) Camarasaurus mount, I just this week had to heft a 20 foot ladder. Despite it being made of lightweight aluminum, it wasn't any fun to manipulate, even with two people. But, and this is key, being near ground level is not an advantage, but a huge disadvantage. Why? First of all, vertebrates use a number of sensory apparatus to judge balance and motion. Because my organs of balance where not at the top of the ladder, I lacked the good physical feedback that a sauropod head would have swaying at 6 meters off the ground. Also, the arc at the top of the ladder (or a head on the end of a neck) moves much more, providing better quality data prior to reaching the point of disaterous disequilibrium. That's just basic pendular physics. Lacking all of this forced me to largely use my eyes to judge perspective, which is a far inferior method, as well as the relative pressure in my arms (mostly my wrists, let me tell you!), which are not primarily designed for that purpose. Despite all of these disadvantages, I made it without dropping the ladder.

Finally, the weight of the ladder relative to the muscular skeletal structure supporting it was pathetic (guess I need to work out more) compared to a rearing sauropod. The cennter of gravity was also much higher (relatively) in the system. All of this meant I had a much smaller range of error I could succesfully recover from. A 15 ton sauropod with 25 kg head in the air at the end of a 1 ton neck (at most) would have far more muscle available to correct for errors, especially since the neck is not dead weight (like a ladder), but itself had ranges of motion and muscles that can adjust posture.

I honestly cannot see how any aspect of the ladder analogy is physically or physiologically correct. This in no way trivializes the other challenges that Kent has laid out in trying to solve the biomechanical issues of sauropod rearing (or lack thereof), but rather than being the more intractible of the two problems, I'm not sure that neuromuscular control is even a valid source of concern in addressing this issue. I would be very interested in data that supports other interpretations.

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com

-----Original Message-----
From: Kent A. Stevens <kent@cs.uoregon.edu>
To: rtravsky@uwyo.edu
Cc: DML <dinosaur@usc.edu>
Sent: Thu, 26 Jan 2006 21:19:07 -0800
Subject: Re: Sauropod Energetics (Peristaltic pump)

Sauropod discussion frequently uses the elephant as an analog for rearing, and the giraffe as an analog for the neck. But the sauropod bipedality story will be far more difficult to resolve than the sauropod neck story (which "only" involves osteology and a reasonable, non-naive estimation of cartilage, at least to reconstruct an undeflected neck). 
 
Now we'll need to quantitatively estimate muscle moments, the center of mass for the portion of the skeleton that is engaged in pivoting about the acetabular axis, the starting and ending poses, and more. 
 
But since it seems so hard to get simple skeletal reconstructions straight (sorry) for sauropods, it looks fun-but-nearly-hopeless to make headway on their rearing up. 
 
Would anyone want to help lay out some ground rules on what would be a convincing (if not overwhelming) argument either for choosing between the two (mutually exclusive) alternatives: 
 
1) that (at least SOME) adult sauropods engaged in feeding bipedally (or tripodally) 
 
or alternatively: 
 
2) NO adult sauropods engaged in bipedal (or tripodal) feeding. 
 
My question is not which is your answer (1 versus 2) but what would be a convincing argument for nailing either alternative. 
 
To be constructive, let's please separate the problem into biomechanics (which is testable for a range of bracketed estimates) and the neural command-and-control coordination issue (which I suspect will be far more difficult to resolve). 
 
[Regarding the vestibular coordination issue, ever walk while carrying an extended extension ladder vertically, like when you are painting a house, and you want to move the ladder around the corner? As the upper end of the ladder sways about its up to you to correct it before its too late. In this case you're on the ground looking up, and you've got a big clever head on your shoulders. In the sauropod's case, its itty bitty head is way up there, trying to reach something to eat while suspended at the end of a dynamically flexing neck that's extended above a swaying trunk supported by perhaps somewhat wobbly legs on uneven ground, and it's got to decide in real time whether the current degree of swaying that feels and sees is within tolerance, or whether its time to take a sidestep, or ...] 
 
and 
 
[Oh, and rearing up for mating is just not the same problem (as we all know). Sauropods could rear up to mate as if partaking in a bit of mountain climbing, engaging the pollex claw as a crampon, and anyway the entire weight of the male need not be maintained in static equilibrium during the mounting. For a sauropod (or an elephant for that matter) to sustain a bipedal posture for even a few seconds is significantly more demanding, and all for a lot less gain, seemingly.]