It must have been some sight indeed!
I would not be surprised if these Aliens used space laser axes (SLA) at first - or some other technology beyond us. It might well appear as magic to us, shedding some light on a few of our ancient myths.
What is clear though is some stayed behind, as is evidenced by archeological finds of inhuman size axes and the like. We can also see evidence of them staying in the historical records of cultures around the world. I posted some pictures of these earlier, but all you'd have to do is flip open your bible to find more.
To try and claim that dinosaurs existed seems to rely mostly on evidence created rather than procured. Its a silly dream meant to help sell science as a profession by showing a gullible age examples of wondrous creatures of myth like dragons. Look at what science can do! We found dragons! Surely we desire not to work and instead play in the dirt.
Looking at the dinosaur rushes, we would have expected all cultures to be aware of these towering giant lizard birds. These bones should be everywhere. Consider those cultures that praised dragons or that held them in a privileged place in their society. Don't you think they would be interested when they found a bone in a shallow river? Interested enough to prize this and preserve it as they did other artifacts of their society?
Dinosaur bones are mostly giant bones, chicken bones, and other large bird bones pasted together to make money. This is why there is no mention of serious study of them until around the same time science was trying to emerge as a profession. Paleontology is a field saturated with fakery and silliness, and paleontologists have historically been shown to be deceitful, dishonest, and in search of fame and money - not truth.
Its been brought up that you've seen fossils - above ground. First off, why are these so opportunely placed if they require years and years of compression to create? Why do they not exhibit a line of thrust? And finally - why are they almost always snails, crustaceans, shell animals, plants, and the like? Why the disproportionate temporal spacing of these finds comparatively to other archeological and biological finds? Because there is a specific time when scientists started faking dinosaurs so they could put them on display in their lobby.
Now that science has been sold as a profession, it has instead taken its place as a religion. A religion of magical dragons, spinning round balls, and magical gravity forces that both use a particle and don't and travel backwards at the speed of light. I call shenanigans.