Dinosaurs became extinct about 65 million years ago, long before any humans existed. The reason why scientists who study dinosaurs reached this conclusion is radiometric dating of the rocks in which dinosaurs fossils are found.
Geologists by the early 19th century had worked out that fossils appear in the geological record in a specific sequence; but it was only possible to date them relative to each other. For example they had worked out that dinosaurs died out at about the end of the Cretaceous period. It was not until the 20th century that approximate dates have been allocated to each of these periods. For about 160 million years dinosaurs were the dominant animal on the earth until about 65 million years ago.
A reason why some Christians have trouble harmonising the great age of dinosaurs to the record of creation in the Bible is not because of any problem with scientific discoveries, nor with any fault of the Bible. It is because of misunderstanding of the Bible.