It was actually in a series of short stories, of which 'Paddles' was one. It's generally seen as more of a one-shot alternate continuity, seeing as it seems that Sludge isn't mentioned in the story.
Of course, for an actual elasmosaur Transformer, there's one third of Magmatro, which can be either an elasmosaur, part of Magmatron's robot mode, or the back end of a tri-dinosaur combination that at best looks sort of like a dragon and at worst looks like a dinosaur orgy gone horribly wrong.
In the wilds of the Congo, the mysterious Mokele-Mbembe is spotted.
Dad's been working on getting the lawn to look its best, so there's now these large patches of long, green grass. I thought they looked nice enough to try a diorama in them, and the idea of a Mokele-Mbembe diorama came about because I thought the grass looked sufficiently tropical to pass for tall African grass.