According to Tallant "The big question in the philosophy of time at the moment or at least has been quite recently is how the presentist deals with... the truthmaker principle."
What is it that makes it true that dinosaurs used to exist? Their bones are (presently) in the ground and museums. We extrapolate along lines of causality and infer they used to exist. So the truthmakers are the (present) bones and our (present) extrapolations.