Stuart wanted to know...
What is the recent evidence that says long-necked dinosaurs held their tails out straight? I liked the older idea that they dragged their tails on the ground.
Well Stuart, for a start there are many trackways known from sauropod dinosaurs and none of them show tail-drag marks (with perhaps one or two possible exceptions).
The longest-tailed sauropods, the diplodocids (Diplodocus, Apatosaurus, etc.) had a distinctive arrangement of the hips, in which the tops of the vertebrae (back bones) that make up the hips stick up very much higher than the main bits of the vertebrae. This arrangement would provide a strong anchor point for ligaments and muscles that would have kept the tail up off the ground.
The hips of shorter-tailed sauropods such as Brachiosaurus have less raised vertebae tops, so their tails may have been less horizontal than those of their longer-tailed cousins. Still, a brachiosaur's tail base would have been a good four meters off the ground, so the tail would have had to droop a long way bit to reach that far down!