User blog comment:GSFB/Goliath of Gath vs Ankylosaurus/@comment-2136224-20130129140717/@comment-5232784-20130129183057

I don't personally know if a lone T Rex could flip an Ankylosaurus: for although its legs are large, thick, meaty enough to perhaps do the job, it would always have to keep an eye out on the Ankylosaurus' tail. Plus, it is a known fact that if a T rex fell down, it cannot get back up again: just like a Giraffe. So it has to make sure it has good balance and try to flip the Ankylosaurus over with a kick, while avoiding the tail. I...don't think that is likely.

However, a fossil find rediscovered (I believe in Montana) showed that it was possible that T Rex lived in packs, so they could use weight of numbers. Plus, if a T Rex bit the head, then it is possible that it could snap the Ankylosaurus' neck with a bite and twist.

Still, some fossils of T Rex show the damage an Ankylosaurus tail could do (I think the famous T rex called "Sue" showed some major damage on its leg from an Ankylosaur strike. Luckily, it didn't kill the T Rex (probably wasn't close enough to land a lethal blow), but it was permanently injured in that leg.