How do you know that? Where you there?
Do the math: T. rex is found in the late Maastrichtian of the latest late Cretaceous, which ended +/- 65MYA. Neanderthal is found in the Pleistocene of the Tertiary, and Cro Magnon is found in the Pleistocene of the Tertiary and Holocene of the Quaternary. Neanderthal is found beginning at +/- 100KYA, and Cro Magnon at 40KYA to present (Cro Magnon is AKA Homo sapiens sapiens, otherwise called US).
Now explain to me how it would be possible for life forms separated by 65 million years of time to exist together anywhere outside of Jurassic Park or King Kong.