It's really great work you've done here, but a few issues I noticed:
The front legs, especially the right one, pop when the leg comes down. That can be simply fixed by moving the front of the chest down a bit every time a front leg comes in contact with the ground (besides, that happens in animal walks anyway, the body overlaps when a foot hits the ground)
The head is swaying left and right, which seems like a very disbalancing thing for the animal. Most of the time, a head is held still in 3D space. Of course, we don't know how a Diplodocus would have walked, but its close relatives lizards and birds tend to keep the head as still as possible.
And the tail here seems to flexible and moves too much. As far as I've seen, reptile tails are much far from the catlike tail whip motion. Also, such big motion might even disbalance the Diplodocus. I might be mistaken on this one, but just a heads up.
you got some pops in the leg. when that foot comes down bring that part of the body down with it as well as leading the body to the extreme characters right or left of you screen. when the back legs move the character should begin to move towards the side of that leg. this will eliminate the pop. think about spacing when you have these issues and add a bit more weight after all they way a lot. great work!
It's a really nice walk cycle and the skeletal structure looks great! The only thing I'd suggest is make the swinging of the tail more closely related to the motion of the rear legs. As of now, it looks like it's swinging (a lot) just to be swinging.