The Eastern Panther is Extinct
The U.S. Fish & Wildlife Service has has determined that the legendary Eastern Panther (also known as the eastern cougar, puma, catamount and mountain lion) is extinct, and likely has been since the 1930s. There have been numerous reported sightings throughout the years, but the FWS says they were other species, "including South American cats that had either escaped from captivity or were released to the wilderness as well as wild cougars from Western states that had migrated east."
Now would be a good time to check out this great 2004 Harper's article about people obsessively trying to track down evidence of the Eastern Panther in Pennsylvania. Looks like they'll never find it.
