I have sometimes wondered whether perhaps adult sauropods, in at least some lineages, NEVER bent their limbs or moved them far from vertical. If that's so, then they would have avoided the enormous joint stresses involved in lying down and getting back up again. But they would have had to do without deep sleep. Then again, since no-one really has much idea about sauropod sleep anyway, I wouldn't discount it.
I once read the idea that sauropods slept standing up somewhere long ago. Of course, it may have been proposed by someone who didn't know that all extant birds and mammals, even ostriches and zebras, lie down _sometime_ in their sleep.
No need. Because unlike giraffes, sauropods had long necks.
I'm _so_ going to steal this.