Lemond used an aerobar in 1989. He got the idea from triathletes, who started in 1984 and maybe earlier. Before then roadies would use a chop and flop set really low. These seem to be the main precursor to bullhorns.
Bullhorns in 1987:
http://youtube.com/watch?v=BBIV2gXV2tM
in 1984:
