"The movement [of the Milky Way] is not edge-on like a Frisbee," Melott noted. Instead, he said, it is flat, "like a pie in the face."

Huh, I didn't know that, and now I have a great mental picture to accompany that fact.

For anyone who skimmed and is wondering "How long before another mass extinction, according to this theory?", the answer is in the last sentence (on page 2): we've still got 10 million good years.