Do you guys thinck it could have been posible for diplodocid sauropods,in the size range of Diplodocus, to walk bipedaly for short periods of time?

They evolved a design wel adapted for lifting their bodies on their hind legs, they are wel balanced for that, they have a very strong back and their hind legs carry most of their mass anywhay. I know they probabily evolved that for getting at leaves high in the trees, I am just wondering if it could be posible for something like Diplodocus to also walk bipedaly for a short time.

I dont thinck that would more implausible biomechanicaly than a 9 tone theropod like Spinosaurus, or an animal like Amphicoelias. What is your scientific view on this?

First off Andriann there is still a fair amout of disagreement between palaeontologists over how well sauropods could rear up. I think it is generally accepted that some could (and diplodocoids would be in that group) but 'well adapted' is not a phrase I would use. Of course one would imagine that most sauropods would have had to had a mechanism to raise themselves in order to reproduce. Males woould have had to mount females to mate and while they could have 'walked' up the back of the female as rhinos and elephants do, one wold imagine that rearing at least part of the way would have been a good start.

As to walking bipedally, it depedns what you mean. I think it is reasonable that if rearing onto their hind legs when trying to mount a female, or reach into a tree to feed they could have taken just a step or two forward as they came down ono four legs. However, to actually 'walk' bipedally - maintain their balance and take more than a couple of staggered steps I think very unlikely. They risk a very hard and potentially dangerous landing, would have trouble balancing, and would be taking aloit of strain on their legs - there is a huge difference mechanically between rearing and walking on two legs, the latter more than doubles the force going through each leg as they try to step.

Yes of course there were 10 and maybe even 15 tonne bipeds (the biggest theropods and ornithopods) but these had evolved to do this, and sauropods had not. It is theoretically possible and witout modelling the bones and potential stresses and ranges of motion of joints, it is hard to be sure, but I can see no reason that they would want to try and doing so would be very dangerous. In short, I think it very unlikely.

David has said most of what I would have said on this, but since I am a sauropod specialist, I may as well throw a couple more points into the ring.

First, if you look at the skeleton of Diplodocus carnegii in side view -- for example, the reconstruction at http://www.skeletaldrawing.com/sauropods/dcarnegii.htm -- you'll probably have a gut feeling that rearing wouldn't have been too hard for it: most of the mass is around the hips, and quite a lot of it in the very long and fairly massive tail.  By contrast, look at a skeleton of Brachiosaurus brancai -- for example, the mount at http://en.wikipedia.org/wiki/Image:Berl … oto_de.jpg -- you'll see that it doesn't look capable of rearing at all.  Those gut reactions are pretty good: R. McNeill Alexander (in 1985 or 1989, I don't have the book and paper to hand to check which) calculated the position of the centre of mass for both species based on reasonably accurate scale models, and found that in Diplodocus is was just forward of the hips but in Brachiosaurus much further forward.  So in Diplodocus, it would only take a small shift to get the centre of mass over the feet, and therefore to rear.  But the Jurassic Park people made the worst possible choice when they selected Brachiosaurus as the sauropod to have rearing in the first-sight scene.

Second, as Dave points out, the ability to STAND on two legs does not at all imply the ability to WALK on two legs.  The latter is an incredibly difficult feat, not only because of the immense mechanical problems, but also because of the brainpower needed to maintain balance -- something that we do without conscious effort but which poor, dumb, Diplodocus would have had big problems with.

Third, while there are ways to calculate where Diplodocus actually could rear, no-one has yet done anything remotely like a rigorous study to assess its likelihood: in fact, no published work has gone much further than "Well, it LOOKS like it probably could".  Serious work on this would need to look at range of movement of various joints, likely attachment points and sizes of hind-limb and tail muscles, stresses in bone and soft-tissue, the problem of landing safely, and more.  We all hope someone will work on this (or maybe already is) but I don't know of any plans in that directions.

So Adriann, if you are planning on making a name for yourself in palaeobiology, this would be an excellent question to work on!  Study anatomy and engineering, and off you go!  :-)