Triceratops is a baby Torosaurus?

[Alyrium Denryle]

Sure, but there were other species around to prey upon in that region, and nothing says that they would be taking down healthy adult individuals. Dinosaurs have a long history of using sheer size to deter predation. The Juvies, which would have outnumbered adults by a wide margin were still on the menu.

And bear in mind, I do not support horners conclusions, only his logic and credentials. My preferred explanation is T rex is this:

Indeed, that's all true.

I must say, I also like the idea that T. rex family groups hunted in conjunction, with juvies flushing prey into the exceedingly deadly jaws of their mother.

I think one reason that most of us resist a scavenging T. rex is because very large theropods are the rule in Mesozoic ecosystems, not the exception. T. rex is big (bigger than an elephant) but not the biggest. I haven't scanned the literature, but I don't believe that other large theropods have been deemed to be so limited in their hunting capabilities. And I don't see any reason why giant herbivores would be drastically faster and more agile than giant tyrannosaurids. Granted, its ability to hide and to sprint are dubious, but as you point out, there are other hunting methods. It just seems reasonable to think that large herbivores would drive the evolution of large carnivores.

This isn't a serious criticism of Horner, of course...frankly, I don't have the time, motivation, or qualifications to offer one at this time.

The problem of course is that unless you have really good conditions (like in the slate fossil beds in china), you are more likely to find the big dinosaurs than the small ones. As far as the literature is concerned, that is just a bias in subject material. T rex is charismatic, everyone knows him, and a lot of work gets done with him.