ANSI adopted function prototypes from C++ in C89. Originally C had no type checking on function parameters. All arguments were promoted to word width and pushed to the stack. If you gave a function fewer arguments it would just read garbage off the end of the stack. If you gave it excess arguments they were silently ignored.

Sort of. ANSI introduced prototypes, but old-style function declarations and definitions, though they were declared obsolescent, remained valid (i.e., any conforming C compiler is still required to support them).

As of the 2011 standard, that's still the case. I think that C2X will finally remove them.