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Re: Sauropod ONP



Jaime, all:

< The issue, I think, is that some restorations and arguments would imply that sauropods were engaging in neck elevating postures as a matter of course, rather than constantly held horizontal.>

Yes, and moreover, some silhouette drawings suggest that those elevated postures come naturally, with little or no deflection away from the ONP (due to inadequate detail in the drawing of the articular surfaces, particularly the zygapophyses, or what is worse, a subtle-but-cumulative distortion in how the vertebrae are drawn).

It is important to "lower the boom" on these exaggerations of ONP. What one might then care to speculate about the fraction of the time sauropods held their necks above (or below) the ONP is just that, speculation.

My colleague Mike Parrish and I speculate that the ONP was indeed the default resting head height and it already reflects some built-in droop, particularly cranially. It has the advantage of holding the head pointing downward, for what we term "downward feeding" and BV (for "Browse by Ventriflexion"), which is the most common form of feeding among large extant terrestrial herbivores including giraffes (!). The latter story might surprise some; enjoy this site and forget what you might have been told earlier about giraffe feeding (but save some of Kipling's "just so" stories for night time):

http://natureinstitute.org/pub/ic/ic10/giraffe.htm

The ONP for the giraffe neck is NOT the maximum of dorsiflexion, as I have shown by modeling then articulating a virtual giraffe neck in DinoMorph (using CT scan data of actual giraffe cervical vertebrae). But the ONP appears to be close to the "average" elevation for standing and walking giraffes. Sometimes they hold their heads nearly vertically while vigilant, but overall the ONP appears to be roughly predictive of the resting position, for adult giraffes.

In our published work and SVP and SVPCA presentations, Mike and I have only attempted to establish the true ONP for sauropod necks. Only recently we've been asked, and have asked ourselves, what ONP might mean. As a result of the very helpful review process for the Curry Rogers and Wilson book chapter we began to examine what is know about the relationship between ONP and behavioral stances in extant tetrapods. It turns out virtually no formal work has been done on this important issue. Observations of captive herbivores in zoos do not necessarily transfer to the natural setting, of course, and we have found little published literature on the relationship between browse height and ONP. There's a lot of behavioral/comparative osteological work to be done before generalizations/predictions regarding the relationship between ONP and, say, browse height, will firm up.

< ... So it seems rather more romantic and "aesthetic" to raise the neck and argue that contradictory theories would be wrong.>

Yes. And in reconstructing an accurate ONP for each sufficiently- complete sauropod taxon, aesthetics and romantic notions simply should not enter into it. Getting the ONP correct remains an inexact process, as there will be a question of how much "wiggle room" to provide in the intervertebral separations, which of course affects the cumulative curvature of the neck. That's where examining articulated series in situ, and extant necks with opisthocoely, becomes important. We find, quite unambiguously, that strongly opisthocoelous vertebrae (and for that matter strongly procoelous cervicals in some other forms) assume an osteological neutral pose, ONP, when three factors are simultaneously satisified: aligned zygapophyses + parallel external lateral margins of condyle/cotyle pairs + very little separation deep within the ball-and-socket. So we don't in fact find much wiggle room in the reconstruction of the overall ONP.

< We should also consider straightening the spines of sauropods BEHIND the shoulders as well >

YES! And that tends to raise the head, particularly when one couples a straighter dorsal column with a more ventral placement of the pectoral girdles as various studies are suggesting. Now, the latter topic might bring on additional rants from some quarters, but let's please spawn a separate thread for shoulder placement, distinct from axial ONP matters.

< ... since ventrally-wedged dorsals seem rare to my knowledge. >

Yes. But there is clear-but-subtle osteological evidence for differing degrees of arch to the back within the sauropoda (as Scott and others are also finding).

< ... but when providing a skeleton that is largely static, there is no reason to diminish the effectiveness of the restoration by exaggerating features for "effect". >

I agree.

Kent