On io9, Ron Miller posted a gallery of his photos of Cosplayers from 1970's science fiction conventions. (NSFW)
This subculture spun off Furries, and it made me wonder if any proto-furry costumes were included. The closest I saw were a bird-woman and insect characters, who could be described as anthropomorphic, but not "furry".
What are the earliest records of organized furry activities? I'd guess these are somewhat underexposed and could be better documented [Yarf #46 (Jan 1997)].