I remember seeing an interview/excerpt from an interview that was highly amusing and really sad..
Basically, the creators of Terra Nova were asked about how going back in time would screw up the timeline, and they didn't have an answer, because they hadn't even thought about it. They just wanted to make a show about humans and dinosaurs living in the same time. They finally said they'll get around to it eventually.
Apparently they never expected viewers to actually think about what they're watching.