Fossils of species X are found in deeper strata whereas fossils of species Y are found in superficial strata. What can be inferred from the above information?

In stratigraphy method, layers of the rock (strata) are used in the dating of fossils relative to each other. Fossils found in lower strata are older while those in the upper strata are more recent. As species X is found in deeper strata, it can be supposed to have originated earlier than species Y.