Palaeocene
Non-avian dinosaurs may have survived to some extent into the early Danian stage of the Paleocene Epoch about 66 mya. The controversial evidence for such is a hadrosaur leg bone found from Paleocene strata in New Mexico; but such stray late forms may be derived fossils. This means they were fossilised, then erosion uncovered them, then they were buried again in a younger layer of rocks.