On Wed, 8 Dec 2010, Tor Bertin wrote:
Generally speaking, the herbivore is going to be holding the cards here. When hunting bulky animals with horns/antlers, carnivores will typically do what they can to attack from the back side of an animal, especially when their front limbs lack the ability to grasp/maneuver tricky prey items. Wolves hunting elk may be a decent analogy here. It's much more likely that a _Tyrannosaurus_ would try to keep as far away from the horns as possible. As long as the _Triceratops_ is facing the _Tyrannosaurus_, I find it highly unlikely that the _Tyrannosaurus_ would lunge forward, unless it was either a. remarkably inexperienced or b. extremely hungry and desperate. Carnivores may be threatened by bluff charges and aggressive posturing, and often times a direct impact isn't necessary to keep the herbivore involved safe and alive.
I would think that the masses involved do not require high speeds to see impact effects.
That said, in all likelihood, large ceratopsians would be much less likely targets than their more vulnerable and less risky offspring.
But which may be defended by the parents or others in the herd...
One thing that also occurs to me is if the rex/whatever were charging or otherwise moving towards the triceratops, would those horns be able to withstand the impact? And as far as the rostral horn is concerned, it probably doesn't have much of an edge, so considerable force might be needed for a similar piercing function. Just how well is a ceratopsid skull built to take impaces?