Science fiction and fantasy cosplay has changed a lot in the last 35 years. Back in the late 1970s, there weren't very many rules, if any. And there certainly was nothing like a separate costuming fandom. There were also an awful lot of naked people (which eventually resulted in the only rule I ever remember seeing posted: "No costume is no costume"), making authentic Edgar Rice Burroughs characters fairly popular subjects.
Here are a few choice examples of 1970s cosplay, from my personal photo collection. Warning: Many of these are NSFW.
One thing I noticed in going through the slides — mostly taken at Worldcon masquerades and a few other cons — is the great sense of whimsy that permeated SF costuming decades ago. This is something that seems to be missing, now that costuming is taken so much more seriously.
I recognize a lot pros in some of those old pictures, too — such as Elfquest creator Wendy Pini as one of her own characters.
Oh yeah — I remember another rule. Food was nixed for costumes after one joker covered himself entirely in peanut butter (he was a turd literally and figuratively), which eventually turned rancid after 3 or 4 hours under hot lights. Oh yes, indeedy, those were the days...
Tars Tarkas
Dejah Thoris
Elfquest's Wendy Pini is on the right
Want to see more cosplay photos from 1977? Here's a second gallery: