They've found completely in tact skeletons of dinosaurs. However, they are not millions of years old. There's accounts of them in the Bible, specifically in Job where a description is given that matches a brontosaurus. There's also accounts out of Egypt from when it still had significant marshlands. Harvestable soft tissue is also not too uncommon in dinosaur bones, but it is too old and degraded for anything like cloning.

There's also cave paintings found throughout the world depicting large creatures.

This might be enlightening: https://www.youtube.com/watch?v=edNFe5SQH7Q

This one specifically covers what dinosaurs were called BEFORE the word dinosaur was invented in the 1800's and goes into more historical accounts: https://www.youtube.com/watch?v=GQPnQp6cMfc

Here's one regarding the soft tissue within their bones: https://answersingenesis.org/dinosaurs/bones/dinosaur-soft-tissue-evolutionists-problem/