Well, we know that dinosaurs are long gone (or so they say)

I just want to know what you think is the cause of their demise.  Here are some of mine

Plagues

It could be possible that the dinosaurs got a disease that could spread fast and kill millions easily. The plague would only affect giant reptiles and such so the other species would be unharmed

Only one sex left

In some reptiles, like the crocs, the sex of the offspring is determined by the temperature (if it's high the croc will be a male, and if it's low it'll be a female) . If a major climate change occured, and Dinosaurs functioned this way, then they won't be able to reproduce.

Magnetic Poles switching

Every few milleniums the earth's magnetic poles switch (so north becomes south and south becomes north, according to the compass). If the dinosaurs had an organ or whatever which could dectect the magnetic poles in order to go to their breeding grounds, they'd be going in the wrong direction and (never find their breeding gronds).

Well, I would like to hear your theories. And I hope it's more original then "an asteroid crashed into earth, blocked out the sun which killed the plants so then all the plant-eaters died, so then all the meat-eaters died" 

[Muerte]

Well, I would like to hear your theories. And I hope it's more original then "an asteroid crashed into earth, blocked out the sun which killed the plants so then all the plant-eaters died, so then all the meat-eaters died" 

  Actually it is a valid theory, but if this were the case, then there would likely be some more far reaching consequences than the extinction of dinosaurs.  How ever what if it were something as simple as a temperature change?  While a small change in temperature wouldn't necessarily kill Dinosaurs, it could easily kill plant life, well that would do the trick.  Remember that the ecosystem of our world is a very fragile thing.  Change somethings environment by only a few degrees and well, chaos city.  Then of course you would have the domino effect.  Not as dramatic, but....

I think that the problem with Dinosaurs and that the reason that they do not exist until now is that they are too big and too wild for comfort. I would have guessed that they would be still existing until now if they had some form of maintaining themselves.  It will be a tough task to do something that you are not sure of and with that type of mentality to eliminate all opponents, that would make sure for killing what gets in your path.