we alikum al salam wa rahmat allah wa barakato
about dinosaurs yes they are true , or how would u think there is oil in the middle east
but about if they were at the prophets time no i dont think so because they were alive millions of years ago and allah had created the earth before he sent adam down to it and he prepared it for the new creature which is " humanity " and in some tafaser "Quran explanation "books it says that Satan and his sons where living in earth before adam but no one can admit that.