It is hard to imagine that creatures as tall as five story buildings actually walked the earth, but we know that they did because we have lots of evidence. 

Their enormous size is probably the reason that so many people are fascinated by dinosaurs. 

What allowed these prehistoric creatures to get so large, and why don't we see larger animals today? 

This informative and entertaining video by PBS Eons will shed some light on the answers to these questions. 

After you check out the video don't forget to leave a comment to let me know what you thought!