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Re: Parrish's neck work ...



>You bring up a good point.  It's difficult to know whether or not
>sauropods could rear.  And yes, Parrish's work does not eliminate the
>possibility that some sauropods reared up on their hind limbs. 
>However, based on what I've seen (I mostly study diplodocid and
>camarasaurid sauropods), it's tough to imagine that if these animals
>did rear how they did it.

I'd like to thank Matthew for his detailed reply - even though much of my
masters and doctoral work was on bird anatomy, so I am reasonably familiar
with the terms he raises, not everyone is and I am glad he took the time to
explain them.  A few comments:

>How a passive tissue could generate enough energy to lift the entire
>front end of a sauropod off the ground has never been investigated. 
>There is a lot of speculation on how or why it might work, but so far
>there have been no quantitative models or studies of this.  Why else
>would you have tall neural spines over the sacrum?

I'm not quite sure why one would expect the nuchal ligament to be involved
in actual lifting, as opposed to simply maintaining the head and neck in
position as the animal pivots upward.  Surely more important here is where
the animal's center of gravity was, and how weight was distributed around
that center (I believe Bakker argued in his book that taking this into
account it would have been much easier for a stegosaur to rear on its hind
legs than an elephant, which has so little of its weight posterior to the
pelvic fulcrum - without knowing the anatomy in detail this seems
reasonable to me, and I wonder how it would apply to sauropods?).  I guess
I have always assumed that the tall neural spines served the same purpose
as the towers holding up the cables on a suspension bridge.  To what extent
can a sauropod (or at least a diplodocid) be compared to a counterweighted
drawbridge or a giant teeter-totter?

>The forelimbs are shorter than the hind limbs.  This does not
>necessarily guarantee rearing either, because it can be argued (with
>an equal amount of speculative energy) that the lower forelimbs got
>the head closer to the ground, where grazing on ferns was possible. 

I fail to see why diplodocids could not have both grazed ferns when on all
fours and browsed leaves when rearing - the two do not seem mutually
exclusive, and given the vast amount of vegetation these things must have
had to shovel into themselves to keep going, I would think that they would
have tried to use every bit of greenery they could get.

>Either way, the shorter forelimbs also have ties to the evolutionary
>past of sauropods.  Early saurischian dinosaurs have shorter forelimbs
>than hindlimbs, and the condition seen in diplodocids may just reflect
>this and have little to do with evolving towards a rearing condition.

I think you may have this backwards.  The ancestors of sauropods were
presumably bipedal; I assume no one argues that even prosauropods were
obligate quadrupeds.  Therefore there was no need for sauropods to evolve
TOWARDS a rearing condition - a rearing condition was primitive for the group.

>The elongate heads with their pencil-like teeth are very weird. 
>These animals did not chew, but swallowed whatever they ate whole,
>because unlike mammals, they have no molars, no canines, etc.  It's as
>if your mouth were filled entirely with pencil-thin incisors.  The
>best you could manage would be to snip off things and swallow them. 
>These teeth don't instantly strike someone as being able to handle
>tough, woody foods or even some of the tougher piney plants.

I have always assumed that these teeth would be quite useful in stripping
leaves from branches - you can get a similar effect by drawing a leafy
branch through a garden rake (or, better yet, use two garden rakes in
opposition).  One might ask why modern browsers aren't built that way, but
of course these are mammals, which (a) rely on teeth rather than gizzard
stones to crush and masticate plant material and (b) have quite different
(I assume based on birds) tongue anatomies.  I would wonder if any dinosaur
could have been expected to evolve a muscular, mobile tongue such as the
leaf-stripping apparatus found in giraffes.

And, even if you
>could rear up, the animal couldn't be very mobile and it would
>unsteady, even with a "tripodal" tail pose.  And how many kilocalories
>are available to it when it gets up in the trees?  Is it spending a
>lot of energy for very little foliage?  Why couldn't a sauropod just
>knock down a tree and eat it that way?

Which raises the issue - how do you knock down a tree?  Surely the easiest
way for an animal like this is to rear, plant your front limbs against the
trunk and bear forward.  Seen this way, an unsteady rearing posture might
be no problem if all that was required was to get into position before
yelling the sauropod equivalent of "timber!".

>Some birds just touch for a second to
>transfer sperm.

As all birds are obligate bipeds (at least on land), I am not sure their
mating habits tell us much about whether or not their quadrupedal cousins
had to rear to do the same thing.  I agree, though, that rearing may not
have been necessary (though if Giant tortoises and elephants can clamber up
into a mounting position, I see no reason why sauropods could not have done
likewise).

One anatomical feature you did not mention: the claw on digit I of the
manus, the only claw sauropods retain (and I gather even that is missing in
some Cretaceous forms).  It would seem reasonable to assume that this claw,
when present, had some function, perhaps defensive - but if so it could
only have been useful if it could be brought into play.  I suppose this
could have been accomplished by lifting the forelimbs one at a time, but if
the animals could rear it may have been even more effective.  Perhaps its
loss in later forms may reflect loss of rearing ability (which in turn -
and here goes a wild, completely unsupported speculation - might have been
less necessary as plant diversity - and particularly angiosperm diversity -
increased at ground level(???)).
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@home.com