From the Time Traveler's Perspective
Imagine in, say, 3011, a time traveler decided to see what it was like on prehistoric Earth. He uses his time machine to hop back to 65,000,000 BC and looks around prehistoric Earth. He accidentally steps on a bee. He then travels back to the future. There is absolutely no human civilization whatsoever. He then ceases to exist.
Events in Chronological Order: Original Timeline
The Earth is created. In 65,000,000 BC, the dinosaurs are grazing happily. They go extinct. Human civilization arises. Everything happens as usual.
Events in Chronological Order: New Timeline
The Earth is created. In 65,000,000 BC, the dinosaurs are grazing happily. Suddenly, a time traveler appears. He steps on a bee. He travels back to the future. With one less bee, the bee hive loses their battle against the nearest wasp nest, whose population grows larger with no bees to deter them. The army of wasps kill all of the bees in the area and all of the wasps' nests grow larger. Eventually, there are no more bees. Thus, not many herbivores evolve. Only a few small ones survive.
Humans never come into being. In 3011, the time traveler appears. For a second, he exists. Then, time catches up with him and erases him from ever having been.