I've been reading Sagan's Cosmos lately and was surprised to encounter the theory that a supernova may have caused the extinction of the dinosaurs - I know the book is almost 25 years old at this stage, but I thought the asteroid theory was fairly much seen as the real cause even then?
Also, he seems to be very definite about the supernova, and does not mention asteroid impact at all, which also surprised me.
The supernova theory was pushed by paleontologist Dale Russell in the late 1970's but absolutely no evidence has been found to support it and it was discredited during debates in the early 1980's.
Believe it or not, the asteroid impact theory was only proposed by Louis and Walter Alvarez in 1980, supported in 1991 by the discovery of the "smoking gun", the Chicxulub impact crater in the Yucatan Peninsula.
  