Before Sonic became a hedgehog, the abandoned character design was a rabbit.
Sega wanted a new mascot who could compete with Nintendo’s Mario, and artist Naoto Ohshima initially proposed a rabbit. The early concept was designed to grasp and throw objects using prehensile ears, which suited a more conventional action-game character.
That idea proved difficult to implement on the Sega Genesis hardware. The development team therefore explored animals that could curl into a ball, a movement that fit Yuji Naka’s fast, curved-tube gameplay prototype. They eventually selected a hedgehog, whose spines also gave the character a distinctive silhouette.
Ohshima’s blue hedgehog design became Sonic, while the discarded rabbit concept did not simply vanish: its expressive, mischievous qualities influenced later ideas, and some related design material was reused in other character concepts. The key point is that the earliest protagonist proposal was a rabbit, not a squirrel, mouse, or cat.