"Ah here we are," your prof stops and gestures at a strange blue haze hovering between two trees. "I discovered this last week when I was hunting gators. It appears to be an anomaly in the space/time continuum. Now, I want to stress that no one should try to touch it; we don't know what it will do. I merely want you all here to observe it." Of course, since he told everyone not to touch it, you know you just have to. You wait through his boring talk about the fabric of time and blah blah blah... Finally he tells the class to move on and help him find a gator for dinner, leaving the anomaly behind. "Hey Chris, watch this!" you tell your buddy Chris. You reach over and pass your hand through the mist. Chris yells and reaches out to stop you, but it's too late. You are sucked into the rift, and Chris gets pulled in along with you. You feel a strange tingling as you pass through space and time, and when you arrive on the other side your arms feel really short. When you look around you realize why that is; your consciousness has somehow been deposited into a T-rex body. You bare your teeth at the triceratops next to you, and he shakes his head at you. "Don't be a dick," Chris says. Anomalies do strange things. "Hey Chris look how short my arms are!" you say, waving your useless limbs in the air. And now that that's done, what should you do now?
Chill man. You're a T-rex. It's cool.
We've got to figure out how to get back to the future and into our own bodies.
It's time to go kill some mammals. If you kill all the mammals now, then they will never be able to evolve, and you can never exist, which means you could never be sent back here to destroy them all, and then what? I've always wondered what would happen in that case.