So there was a prototype for the humanoid form?

Nasu: ORT will unfailingly use any means available to survive. He's a like a machine that keeps choosing for as long as options exist. Therefore, if taking a humanoid form is what will get him to keep going, he would do it. So that's why he pulled off the most absurd of his absurdities: unlawfully copying human history, simulating 140 million years, creating a timeline where he becomes a Heroic Spirit, then summoning himself from there.

Nasu and Takeuchi's 8th Anniversary interview, part 2 (on U-Olga, Daybit, and ORT)