What is really the earliest known dinosaur?

I think you are correct, that is the oldest found yet.... but is it the Oldest?

We will never maybe know.... in many years after Me and You are gone... say year 2100 they could find remains of even older Dinosaurs... We was never around in those days and its only by fossil records that we know about how old these Creatures where.... and the more we find as far  as New Species then there is a chance some of them would carbon date to being even older... until that happens then the oldest we have found is the oldest... but we dont know what is the actuall Oldest as even older ones may yet to be discovered.

It depends on how far back in the dinosaur's evolution. Does the question extend to only True Dinosaurs?

Hmm, where was it found?