Was the ethical requirement to discuss and acknowledge predecessors work as developed in Newton's time as in our own? I would naturally expect not because it would seem to me to be the kind of thing that develops over time, but I could be wrong as I am not a historian of science.

It's a not a requirement, it's just a natural to do as a research scientist and a student of knowledge to acknowledge prior contributions if you knew it. The same is true when you are at the time of Aristotle.