A few years back I discussed the origins of the 29er with Joe Breeze. Breeze believed that it was the principle of using wheels that were larger than standard 26 inch ones that was important. In his opinion the exact size of wheel used was less important
Before 1990s there where a handful of larger wheel/tyre sizes being used for off-road riding.
Cylocross riders where mainly using narrow knobbly 700c tyres that where only slightly wider than toad tyres.
The French VCCP and English Roughstuff riders used using 650b x 40mm French randonneur balloon tyres,
In Finland they where using a range of sizes of large diameter heavily treaded snow-tyres including 700x47C, 700x44B (44-635 ISO) and 650x54B military bicycle tyres.
The UK 'Tracker' (dirt-track) riders where using knobbly 650x35A tyres originally developed for cycle speedway racing in the late 1940s.
In the US and Europe from 1985 there where 700c Hybrid tyres. Though I remember many of these as being fairly smooth road style tyres.
Of all these larger than 26" off -road tyres, it was the Finnish 650B and 700C tyres that inspired Gary Fisher to invest his money in developing the original Nanoraptor
As Fisher says in the video, he was sent these tyres by UK MTB Pioneer Geoff Apps who had been using them on his own bikes since 1979.