I remember reading a short story in a (I think) multi-author compilation many years ago. The vintage was probably 60s-70s. A time traveller was warning modern people that he had travelled to the era of the Dinosaurs and discovered that they has 'guns' and other technologies and their extinction was actually caused by warfare amongst themselves. I remember he gave some explanation as to why the technological artefacts did not appear in the fossil record, but I can't remember what that was.
Does anyone know what this story was called and who wrote it?