I have never understood that as an argument that dinasaurs never existed, or any other species. Certainly they existed and they died off, and we know approximately when. Do not get your insight from creationists.
If you wish to think that God killed off one species and then created another, you still could not dispute that all these species known to science did not exist millions of years in the past.
The record of their existence is a history of the species of the world. How they managed to change from one species to another is theory. We do not have a final theory of biological evolution, just like we do not in physics. But that does not mean that electrons and photons do not exist. We have experimental evidence that they do, just like dinasaurs did.
What creationists fail to understand is the tremendous genetic variation in a single species. So if part of a species is isolated from the rest, it is easy to imagine that over millions of years they would become a separate species.
We have evidence of man made genetic variation in a single species using the separation method. Take dogs for example. Look at the tremendous variation of size and shape within that one species that can be accomplished is just a few generations by careful breeding.
So there is both theory and data. The creationists try to blind the world to the data by concentrating on the theory. But just as in physics, it is the data that counts, not the theory.
Are you ready to talk about the science god gave us thousands of years ago compared to the science god is giving us today? That is where I wanted to go when we started conversing weeks or is it months ago.