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Re: Long-necked stegosaur, head tail mimicry?



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 wall all the time (that is, the extra calories need 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

www.skeletaldrawing.com

-----Original Message-----
From: Raptorial Talon <raptorialtalon@gmail.com>
To: dinoboygraphics@aol.com
Cc: dinosaur@usc.edu
Sent: Wed, 11 Mar 2009 11:14 am
Subject: Re: Long-necked stegosaur, head tail mimicry?






"The idea that sauropod necks evolved to prevent them from having to walk during grazing has to rate as one of the most ludicrous explanations to ever enter the paleo literature (seriously, it's the energetics equivalent of saying the long necks were snorkels that let sauropods rest comfortably under 30 feet of water)."

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?

Of course, ferns and other foliage of the time apparently aren't quite
as energy poor as once thought, and it could be that maintaining
*such* a long neck would only be useful as a means to access treetop
forage during times of environmental stress or somesuch . . .

Hmm . . . do all the longest-necked sauropods come from similar
environments? The kinds with mostly-horizontal necks, I mean, not
necessarily stuff like brachiosaurs. And, contrarily, do the ones with
the shortest necks also tend to come from comparable environments?