Two items I can recall some scientists looked into that puts the T-Rex out of the much vaunted super-predator catagory - it had a highly developed olfactory setup on par with that of a buzzard, and a measurement and subsequent simulation of how the legs worked revealed that it couldn't run and would fall flat on it's face if it did. Chances are it was just a big nasty scavenger properly equipped to gorge on the large carcasses of the day and probably wouldn't turn down opportunity at anything small, slow or dumb that came into reach.