http://www.biologynews.net/archives/2010/11/15/t_rexs_big_tail_was_its_key_to_speed_and_hunting_prowess.html
The Trex's tail muscle made it so athletic. The muscle helps make it one of the fastest of its time. He compared the trex tail to present day reptiles. This showed him just how strong it really is. He also found out that the ribs, which give the power, are much higher on the Trex.

I think this shows us how athletic and fast they really are. this spead causes them to be able to catch its pray. this also means without that species dieing out we would not be alive today. I say we better be glad they died.