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Re: Long-necked stegosaur, head tail mimicry?
So I suppose I'm back to the habitat question. I'm wondering if long
necks are correlated with seasonally arid environments, where being
able to reach any available foliage in (comparatively unaffected)
riparian zones would be critical to survival during the dry season
and/or periods of prolonged or irregular drought. Conversely, one
could then predict that the shortest-necked sauropods would tend to be
found in the areas least subject to seasonal aridity.
Predator-defense seems counterintuitive to me. Extending the length of
blood vessels and trachea potentially exposed to attack seems far less
suitable than the titanosaur approach of dermal armor, or the
shunosaur approach of active deterrence via a non-vital, fully
weaponized portion of the anatomy. Even having oversized manual claws
and rearing up to lash out with them makes more sense from a purely
Sexual selection hypotheses imply that one gender or other should have
distinctly longer necks than their counterpart, but even if that's the
case, AFAIK the other gender's neck is always still pretty damn long -
certainly well in excess of what's necessary for grazing purposes.
I wish I had time to review the literature to see if I could pick out
a rough environmental correlation.
On Wed, Mar 11, 2009 at 12:59 PM, <email@example.com> wrote:
>>>> Just because I'm interested, how do you think the energetics question
> relates to efficiency of food processing in this case? Modern grazers
> (and of course derived ornithischians, as well) have complex chewing
> mechanisms to go along with their extensive gut floras. Given
> sufficiently low-calorie fodder, couldn't a long-necked sweep-graze
> pattern be a useful adaptation for conserving energy?<<<
> I did some back of the envelope metabolic equations once, and if you combine
> them with estimates of increased respiratory cost it's pretty much more
> expensive just to have the neck then it is to walk all the time (that is,
> the extra calories needed each day to sustain the neck is more than the cost
> of locomoting constantly during the day). So there isn't even a theoretical
> way to benefit energetically, regardless of time spent on oral processing.
> In some sauropods the necks may well have allowed them to reach food
> (energy) that was otherwise out of reach; that's a very different selective
> gradient, and going where the competition cannot yields much larger benefits
> more rapidly (i.e. it's easier for selection to favor). Of course in some
> cases there could be reasons totally unrelated to feeding; necks could be
> sexy (it would certainly fit in with the Handicap Hypothesis for an
> indicator of survivability), they could have anti-predator uses, etc.
> Perhaps neck length was not achieved for the same reason in all sauropods.
> I will point out that specialized low-browsers like Nigersaurus and
> Brachytrachelopan seemed to shed their excess neck length quite quickly. So
> perhaps a more enlightening question would be: Why do they shorten their
> necks, and what does it say about other sauropods who did not?
> Scott Hartman
> Science Director
> Wyoming Dinosaur Center
> 110 Carter Ranch Rd.
> Thermopolis, WY 82443
> (800) 455-3466 ext. 230
> Cell: (307) 921-8333