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Re: Preview of new stegosaur plate paper

Don Ohmes (d_ohmes@yahoo.com) wrote:

<To be honest, when I asked the question, it never crossed my mind that
antlers, horns, and ears would be classified as display structures in the sense
of display as primary function, in part for the reasons you mentioned. So I
guess I should have written "pure display". However, horns, ears, tusks, and
antlers aside, the birds alone satisfy me that the proposition, even
re-written, is probably incorrect.>

  Well, purely display function is rare in nature and usually restricted VERY
sexually dimorphic animals, among them some mammals and birds. Obviously,
waterfowl, landfowl and ratites are very dimorphic birds whereas other birds
tend to exhibit monomorphic body form, especially in the "higher land bird"
groups such as parrots, pigeons, passerines, and raptors. In these birds,
behavior plays a more important role in sexual selection than does morphology
(well, not entirely, they may still be visually dimorphic, such as coloration).

  As regards agonistic structures, while elephants and rhinos DO use their
equippage in combat, as do the antlered deer, often (and preferrably) the
"having" is better than the "using." The using may still lead to injury and
fatality, and while they are hard pressed to sire the next generation, their
immediate well-being is a priority, so unless the other combatant really wishes
to "go at it," visual displays will serve. I can offer anecdotes of visual
displays between bull elephants tossing their heads, waggling their ears, and
waving tusks and trunks and blowing dusts as proof of their power, and this is
often enough to prove the superior male; it is rare, I understand, for two
males to actually FIGHT. Thus the structures may be positively selected as
display features, rather than agonistic, though this alternate function may
have selected for aspects of anatomy (interlocking of antlers, for example).

  In another analogy, the second most dimorphic mammal after man is the lion,
in which the male's mane is indeed a sexually selecting visual cue, and offers
absolutely no inferrence of physical behavior, since it probably won't catch in
the opponent lion's throat or perform stunning visual tricks with irridescent
pelage and thus win in a fight. Fitness to mate may be clued in to the size,
extent, and color of the mane, and thus males may use these to compete with one
another, or prove their prowess to a female, which have been shown to choose
the "black" lions over the "blondes" (maybe I should dye my hair black...).

  Here's a quickie link to news on that study:

  And here's the published study by West and Packer (2002):

  In this study, a deficit in physical fitness confers an inversely positive
selection of partners, as "bigger, longer and uncut" means "hot, sweaty, and
more panting" for males that "get the girls." So not all positive selective
features are really good for the _individual_. Thus this (to bring this back to
dinos) may allow sauropods to have huge necks even IF they weren't better
Hoovers for it, or suggest that stegosaurs sacrificed flexibility for visual
cues and regulatory function.

  Ken Carpenter's 1998 paper on stegosaur spike position, spinal inflexibility
and tail function (of which follow-up research by Sanders, Carpenter and
McWhinney was presented at the 2002 SVP meeting, so a paper will be forthcoming
addressing the mathematical issue of effective tail use) is here:
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Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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