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Re: Parrish's neck work ...



Interesting subject!  There are a lot of topics here and it is a bit hard
to keep them all straight.  With regard to an ability to rear up, I wonder
if the flexibility of the tail has been investigated in the same manner as
the neck.  The old T-rex mount at the AMNH required the tail to be
"broken" for the upright pose.  Does the evidence we have now indicate
that sauropod tails would be flexible enough at the base to allow such
movement?

If they were to rear up, or put their heads down, blood pressure would
have been a problem.  I'm not sure it would have been insurmountable.
Retes to serve as capacitance vessels could have served as buffers to the
pressure, as could powerful muscles within the walls of the arteries
themselves.  It will be hard to find enough soft tissue to prove this in
any case.

As long as their necks have lateral flexibility, I can come up with
another possible function for the length.  One of the big mysteries of
sauropod metabolism is how they got enough food in with their teeth and
how they processed it.  If they raked and ground with gastroliths, that
would be a start.  Hind gut fermentation could have released a lot more
energy, and is used by modern animals lacking the teeth and stomachs for
rumination.  The problem with hind-gut fermentation is getting the food
back in where it can be absorbed.  A long neck to reach around laterally
and rake-like teeth to scoop would help.  A quick long neck would be even
better, preventing any other nearby herd members from stealing their
hard-earned second helping, but perhaps that is stretching things a bit
too far.  A small brain would also be an asset to avoid thinking about
this too much.
Frank

Matthew Bonnan wrote:

> Hi Ronald:
>
> You said: "I am curious that no one has mentioned rearing here.  If
> any sauropods
> could rear, there would be no need for them to flex the neck upward
> to any
> degree as the rearing would do that for them - but a considerable
> degree of
> ventriflexion might be extremely useful to a rearing sauropod trying
> to get
> at some tasty foliage on the far side of a tree.  Of course, if
> rearing was
> part of their behaviour then Parrish's discovery does not mean that
> they
> could not feed in trees - only that they had to rear to do it."
>
> 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.
>
> Let me explain a little bit further what I mean.  My opinions aside,
> here is what we know about diplodocids (the sauropods usually
> considered to be rearing):
>
> 1. These animals have elongate, horse-side heads with small,
> pencil-shaped teeth.
>
> 2. The forelimbs of diplodocids are significantly shorter than their
> hindlimbs, so that the animal's  shoulders were below the hips.
>
> 3. There are tall neural spines on the vertebrae which are
> concentrated at the hips, above the portion called the sacrum.
>
> 4. The femur, like most dinosaurs, has a landmark called the fourth
> trochanter -- this a small ridge located about halfway down the femur
> in sauropods.  In dinosaurs like T. rex, it is located closer to the
> head of the femur.
>
> 5. The tail is elongate, has sled-like chevrons on its underside (in
> case you don't know what chevrons are, they are the bony spines that
> protrude below the tail vertebrae that protect the delicate arteries,
> veins, and nerves), and, where complete tails are available, a
> whiplash-like tail end composed of several, finger-sized vertebrae.
>
> Arguments for or against rearing in sauropods center on these
> characters.  Let's start with the sacral spines, as these are usually
> cited as evidence for rearing.  The assumption is that a large nuchal
> ligament ran off the sacral region, across the back, and inserted
> itself on the neck or back of the skull.  If you're unfamiliar with
> what a nuchal ligament is, it is a rubber-band like tissue which in
> mammals runs from the shoulder vertebrae to the back of the skull.  It
> is a passive tissue.  That is, like a rubber band, it can only store
> energy and release it, but it cannot generate energy on its own.
>
> Let me give you an example.  A buffalo has a very large head which
> would be difficult to lift up if it dropped its head down to graze.
> When it does this, the nuchal ligament in its neck stretches and
> stores the energy imparted to it by the neck and shoulder muscles.
> When the buffalo relaxes its neck muscles, the nuchal ligament
> "springs" back, releasing the stored energy and helps to bring the
> buffalo's head back up.
>
> 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?
>
> Perhaps (but this has not been investigated either) to hold up that
> long tail.  From the footprint evidence, we have never found a tail
> drag mark from sauropods.  The use of nuchal ligament in the tail
> would seem to make sense, and the height of the sacral spines would
> give it a good angle of insertion on the tail.  BUT this is still
> speculative -- someone has yet to do a model or test or whatever.  I
> provide it only as another alternative to the height of the neural
> spines.
>
> 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.
> 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.
>
> 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.  Again,
> even if the sauropods get their heads up in those trees, how they were
> used and what food was available for them to break off and swallow is
> difficult to know.
>
> The fourth trochanter is the site of attachment for a big tail muscle
> called the Caudofemoralis longus, which was the prime mover of the
> thigh when these animals walked (as it is in living alligators and
> crocs today).  How this muscle would have been affected when the tail
> it was attached to was bent away from the femur has never been
> investigated.  Again, we need more information.  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?  There are no good answers to
> these questions right now, but speculation abounds.
>
> The tail and its sled-like chevrons have been argued to have
> supported these animals, with the chevrons providing a "base" for the
> tail during rearing.  Again, no models or quantitative study has been
> conducted along these lines.  Plus, many of the Chinese sauropods have
> sled-like chevrons, like Mamenchisaurus and Shunosaurus.  Not too many
> people have argued that these animals reared up, probably because some
> of them have club-like tails which may have served as weapons.
> Perhaps the sled-like chevrons protected the tail blood vessels and
> nerves when the tail was violently thrust side to side.  Could the
> whip-like tails of sauropods have chevrons for the same reasons?
> Again, speculation abounds but these are great questions waiting for a
> modeling and functional morphology study.
>
> But, didn't sauropods rear to mate?  Not all vertebrates rear up on
> their hind legs to mate.  This assumes that male sauropods had a large
> single or hemi-penis which could only be inserted into the female by
> mammal-like mating rituals.  Some birds just touch for a second to
> transfer sperm.  In some mammals, like certain cammels, the female
> lies sideways on the ground while the male mounts her from the side.
> Again, another great area for investigation.
>
> These are weird animals.  The temptation is great to compare them to
> elephants and giraffes (because that is all we have alive today), but
> we must be extremely careful not to let our generalizations go too
> far.  Saruopods are huge, strange, saurischians.  Even their
> relatives, the birds and crocs, are quite derived.  This is why we
> desperately need good functional studies that go beyond the vast
> generalizations and analogies to living vertebrates.
>
> I hope this helped you and some others.  The rearing question is not
> settled, and it will take many more years of research to gain a better
> understanding of just what those weird and loveable sauropods were
> doing.
>
> Sincerely,
> Matt Bonnan
> Dept. Biological Sciences
> Northern Illinois University