RE: rearing sauropods

["Tracy L. Ford" <dino.hunter@home.com>]

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
Nick Longrich
Sent: Wednesday, January 02, 2002 12:48 AM
To: dinosaur@usc.edu
Subject: rearing sauropods

>In a message by Nick L.

        Perhaps the greatest problem with the "vacuum cleaner"
hypothesis is the predictions it makes when compared against
observations of diplodocid neck structure. You would predict to see a
great deal of lateral flexibility to sweep the neck back and forth
across the feeding area to get as much vegetation as possible.
Vertical flexibility, however, should be relatively poorly developed-
the neck would only need to reach from ground level to a few meters
above in search of low-growing vegetation and shrubbery.<<
Actually, it's not a problem. You seen around cervical 4-6 (I think) they
are beveled down so the neck actually bends down around there and the head
easily reaches the ground with little or now effort.
>> This is the
precise opposite of what you see in Diplodocus according to Stevens
et al. where vertical flexibility is considerable but there is
relatively little horizontal flexibility. It fits a little better
what you see in Apatosaurus, but Apatosaurus has a proportionately
shorter neck than Diplodocus. This suggests that whatever the purpose
of the really freakin' long neck seen in some sauropods was, at least
in the diplodocids it wasn't to forage on the ground. My suspicion is
that mamenchisaurus and the other chinese longnecks are going to look
like Diplodocus but I guess we'll have to wait for that study to be
done.<<

What they are doing is looking at the back of the neck and not the front of
the neck. IMHO the length of the neck has no direct effect to vertical
feeding. Diplodicds necks bend down (from the middle) and it's no problem in
feeding on the ground. If you look at an elephant it has solved this by the
evolution of a muscular trunk. It doesn't need a long neck the trunk does al
the work. Every genera of diplodocid has a different neck length, why if
they all eat from tree tops? Wouldn't they want to have a neck the same
length? Barosaurus has the longest, then Diplodocus, Brontosaurus and
Apatosaurus (yes I think they are different genera!). Also the width and
height of the necks vary. Apatosaurus has a 'wide' neck, Brontosaurus has a
'high' neck. Why all the differences?


>>Simple, you DON"T rear up! Rearing sauropods IMHO is a myth. Actually my
comment and the following is Nicks.

        Regarding elephants, it seems to me that they do more to
support Bakker's rearing hypothesis than refute it.  For one thing,
the fact remains that elephants can and do rear up, if only often
enough to perpetuate the species, despite the fact that they aren't
particularly well-designed for rearing. The first problem is that the
forelimbs, not the hindlimbs, usually bear most of the weight of the
animal in elephants (as in most mammals). Second, the center of
gravity isn't located particularly near the hips. This means that
elephants have to bend their knees to rear, in order to put their
feet below the CG and remain stable. This subjects the femora to
bending stresses, where the breaking point will be lower than if the
limbs are loaded axially and function as columns.
        Sauropods on the other hand, were much better suited to
rearing (particularly diplodocids), as they suffered neither of these
design problems:
        First, the hindlimbs bore much more of the weight of the
animal, and so accordingly were much more robust than forelimbs, the
reverse of your typical mammalian situation (check out d'Arcy
Thompson's _On Growth and Form_ with respect to this observation.
Check him out if you're in any way interested in biomechanics or
morphometrics, too). You've also got to consider that sauropods had
to walk, so the amount of load being placed on a single hindlimb with
the other foot off the ground may well have exceeded 50% of the
animals weight. So putting all the weight on the hindlimbs, or the
hindlimbs with the tail, probably didn't even come close to the
breaking stress of the femora. This varies from sauropod to sauropod
of course. Another thing to consider is that the stresses involved
are going to depend in part on the weight of the animals- some of
these guys may have been a lot skinnier than typically reconstructed,
and some, for all their length, are mostly air-filled neck and
whiplash tail.
        Second, the center of gravity is much nearer the acetabulum
than in elephants, because the front of the sauropod is filled with
air, the forelimbs are pretty small, and the rear is pretty much
solid, with a huge, muscular tail extending behind. Little if any
bending at the knees would have been necessary in a bipedal/tripodal
sauropod; instead the femora may have functioned as columns loaded
largely in compression. This is to an extent true of all sauropods
compared to elephants but especially so in Diplodocus, Barosaurus etc.<<

With the majority of weight around the hips would also make it easier for
the animal to walk, and turn for that matter.

>>        As for high neural spines, having the highest spines over the
hips implies again that most of the load of the body was suspended
from the hips (sort of like the pier of a suspension bridge being the
highest point) rather than the forelimbs (high neural spines are
generally over the shoulders in mammals, e.g. bison). The unusual
height of the neural spines in some sauropods may also suggest that
there were some unusually high tensile loads being supported by the
ligaments and muscles attaching to the neural spines, since the
greater the height of a beam (in this case the spine) the greater its
bending resistance. Again, if this doesn't make sense check out
d'Arcy Thompson for a more extensive discussion of this stuff (he
even refers to diplodocids and stegosaurs in particular) and a really
readable intro to beam theory, tension, compression, and all that
stuff. Basically, most of the body was already suspended from the
hips, so suspending the whole darn thing is hardly a stretch.<<

Your right, tall neural spines doesn't equate to bipedal standing in
diplodocids. Look at Ornithopods, many have tall neural spines over the hip.
In Shantgosaurus the front of the pelvis has short spines while the back has
the tallest and goes onto the tail (also Kritosaurus), Lambeosaurus have
tall neural spines from front to back in the pelvic area, while the
hadrosaurs have short spines but some got really big.

Tracy L. Ford
P. O. Box 1171
Poway Ca  92074