F-Zero GX Easter Egg - Billy's Super Monkey Belt

The apelike character, Billy, is wearing a belt with a face imprinted on it. It's hard to see in the actual game, but is very clear in official artwork. The imprint is the face of Aiai, hero of Sega's Super Monkey Ball. Both Super Monkey Ball and F-Zero GX were developed by Sega's Amusement Vision studio.