Theory - Dinosaur Extinction vs Gravity

I've long had a thought about the extinction of the great dinosaurs that seems in complete contrast to current theories. I suspect it's because mine is full of flaws (like that the period of extinction spans thousands of years perhaps) but it's always made me wonder.

So, here it is:

Dinosaur Extinction Theory
Forget notion about some catistrophic event (e.g. Meteor strike) or climate change - both of which have merit. My theory is that it was Gravity. How so I hear you ask?

Well, lets look at our current biology. The largest terrestrial animal is the elephant - nothing bigger, yet bigger is supposedly good. What about Giraffe? Their necks are so long, that if they fall to the ground and are unable to right themselves quickly, the blood flow rushing to their heads will kill them. Then consider the largest animal - whales. They can exist in their watery environment, but beach themselves and they are suffocated by their body mass. And lastly, consider man. The tallest a man can get is something under 7 feet. When this has been exceeded, the individuals have died young because of organ failure - they're simply unable to cope with the size of the individual.

Yet, we're meant to accept that terrestrial animals perhaps 5-10 times larger than the largest terrestrial being currently in existance lived for Eon's on the planent! Please...

Something drastic has had to have changed - and surely all this can be is the effect of gravity. The cause? Massive meteorite strike? Perhaps an abundance of meteorite strikes over a prolonged period causing a gradual build up in the mass of the earth (yes, yes, I know, a grain of sand added to huge boulder isn't going to make an significant difference - but hey, it's my theory and I'm allowed to make this up as I go along). Could it be that the subterranian magma effects have changed over time (increased cooling has lead to increased mass)?

Who knows? All I know is that the paradox between what we know today vs what we're told to accept from prehistoric times worries me - and this presents a possible explaination.

I actually found someone (who I must admit coined the theory before I had, but I'd long thought about it myself but had never put it in writing) who also pushed this theory. He was an Iraqi scientist but as this was just before the Iraq war, I felt uncomfortable talking about such trivialities with him and thus never sought out his opinion. Pity, I don't even know if he's still alive...