Re: Dinosaur tail dragging

[Dinogeorge@aol.com]

In a message dated 98-09-05 13:32:07 EDT, 102354.2222@compuserve.com writes:

<< If there was, for example, a strong
 ligament running along the tops of the tail vertebrae, and the ligament was
 anchored, say, over the hips, then the tail would naturally tend towards
 being held up, the same was a suspension bridge is held up by the support
 cables above the bridge itself (this is, in fact, how sauropod necks are
 suspended and held up). >>

I'm not at all sure that this analogy works. For one thing, in a suspension
bridge, the bridge is held up by suspension (hence the name) between >two< (or
more) end points. There is only >one< end point for either neck or tail in a
sauropod. So a better analogy would be a cantilevered bridge. Try as I might,
I've been unable to see how a single ligament running along the tops of the
neural spines of either the neck or the tail could hold >anything< up off the
ground. With nothing to anchor it at the far end, everything just flops apart.
Instead, I think we must examine the details of the articulations between the
vertebrae--how much leeway for movement there was, for example, and what kinds
of ligaments might have been present--before we can fully understand how
sauropod necks and tails were held off the ground. The situation is >much<
more complicated than it seems.

In certain cases it's fairly clear that longitudinally elongated cervical ribs
(euhelopodids, mamenchisaurids, camarasaurids, brachiosaurids, ?titanosaurids)
were chiefly responsible for supporting sauropod necks, as long as one
imagines the existence of suitable mechanisms for locking the ribs together
when the animal wanted the neck in a stable position and unlocking them when
the animal wanted to move the neck. In other cases (diplodocids,
dicraeosaurids), sauropod necks were likely supported by numerous ligaments
between tall neural spines--it is very seldom (I think "never") that you find
>both< elongated cervical ribs and elevated neural spines in the same sauropod
neck.