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Re: dinosaur humps (was Re: A Whole Bunch Of Questions)

Jordan Mallon wrote-

> >I prefer Bailey's evidence for humps.  Certainly better than any
> >argument for sails.
> Perhaps better than any published argument for >thermodynamic< sails, but
> what about display, mimicry, etc.?  Bailey barely touches on the other
> possibilities.  He insists that the transverse narrowness (and sagittal
> broadness) of the neural spines indicate an increased resistance to strain
> in the anteroposterior plane (thus implying a muscular hump of some sort).
> But don't most dinosaur neurals, whether tall or not, exhibit similar
> dimensions?  Why couldn't dinosaurs have just elongated them to form a
> without changing the aforementioned dimensions?

First of all, a dorsal hump would still increase surface area for
thermoregalatory function, and still be useful for display.  Second,
virtually all dinosaur neural spines are indeed transversely narrow blades
(one of the few exceptions that come to mind is the posterior cervicals and
first dorsal of Sinraptor), but they also functioned as attachment sites for
muscles and ligaments as Bailey argues tall neural spines did.  So "just
elongating them" without changing surrounding anatomy would cause a hump
instead of a sail.  Animals with sails (eg. lizards, presumedly basal
synapsids and Amargasaurus) have rounded neural spines, which are more
efficient for a sail that has no biomechanical function.  Finally, it wasn't
just the transverse narrowness of the spines that supported Bailey's
argument, but also the sagitally expanded distal ends which are roughened,
I-beam cross section and attached ossified tendons (in ornithischians).

Mickey Mortimer