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Re: Long-necked stegosaur (the reason for long necks?)




Hello everyone,

Sauropods had relatively high ground loading and limited traction. Any
terrain too soft, too unstable, too hard, too uneven, could be problematic.

This has impacts beyond simply keeping Sauropods out of some environments: In essentially any habitat type, there would have remained patches of food which would be inaccessible. The question is only the percentage of food that would be inaccessible in a given habitat.

The obvious solution is to grow a longer neck. You can reach to consume
foliage growing in ponds, you can consume ferns dotting a rocky outcrop, you
can pass in between >500 ton trees to feed on the undergrowth behind them -
if you have the right neck.

So, having a longer neck, especially if there is competition over food
gathering, is the only feasible solution for herbivores that weight more
than ten tons. I'm a little mystified why this isn't more widely advanced
(in fact I haven't seen it anywhere in the literature). There are a lot of
interesting hypotheses regarding sauropod neck length (I counted ten last
time I checked), but this may be the simplest and most obvious one.

Anyway, the basic point is that we tend to over-idealise the environments
that could have existed. A lot of adaptations make a lot more sense if one
considers how animals could exist in contemporary terrains.

Even something as simple considering width (a characteristic all too often overlooked) can lead to interesting conclusions: One can guess that Tenotosaurus is laterally flattened (and elongated) for moving through woodlands/scrub, whereas, Sauropelta has adaptations suited to comparatively open, exposed environments.

It would be interesting to find out what the rear half of Miragia and
whether there are any Kentrosaurus like spines that might have effected
mobility in some terrain types. If the animal can rear up on its hind legs,
that might also have an impact: Even a few percent more calories from being
able to reach the lower branches of trees may be significant at evolutionary
time scales. If you throw in some exotic environmental factors (eg.
involving drought or fires in some types of floral communities)...

S!

-Jonas Weselake-George

P.S. Regarding neck calculations in a given environment its important to
recognise the role of 'edge' effects (as used in conservation ecology
theories) in heterogeneous terrain. This is import for calculating the
amount of accessible food increased by neck length for any given corridor.
It may also be important for considering the long term impact of Sauropods
on plant community structures.

P.S.S.
I have doubts about the energetic argument that has been advanced for
Sauropods using the neck to sweep through vegetation without having to walk.
But it is interesting to note that the energetic cost may have been greater
for toppling dozens of trees (instead of using the neck to penetrate deep
into a stand of trees). There would even likely be energetic costs to
holding a position on a slope or on terrain which require the feet to be at
significantly different heights - so the two hypotheses may have some
overlap.




----- Original Message ----- From: "David Marjanovic" <david.marjanovic@gmx.at>
To: "DML" <dinosaur@usc.edu>
Sent: Sunday, March 08, 2009 2:17 PM
Subject: Re: Long-necked stegosaur, head tail mimicry?



We assume, like sauropods,
that stegosaurs are relatively slow moving, and the phrase
"sauropod-mimic"
is being freely used, so maybe, just maybe, this particular stegosaur was
doing just that. Not moving very much but being able to cover a lot more
ground whilst eating, moving the long neck in an arc, maximising the
energy
intake without moving very much. Just a thought.

But is it even the case that holding the neck far out and moving it around
costs less energy than walking a step?