Final answer:
Dinosaur fossils are unlikely to be found in the same layer as mastodon fossils due to the significant time difference between their existences; the Law of Superposition suggests they would be in separate strata.
Step-by-step explanation:
It is unlikely that fossils of dinosaurs will be found in the same layer as the mastodon fossils at the site in Siberia. Dinosaurs and mastodons did not coexist; they lived during different geological periods. The Law of Superposition, which notes that in undisturbed layers of rock, the oldest layers are on the bottom and the youngest are on top, implies that fossils deposited tens of thousands of years apart would be found in distinctly separate strata.
According to paleontological data, dinosaurs became extinct at the end of the Cretaceous Period, about 65 million years ago. Mastodons, on the other hand, lived during the Pleistocene Epoch, which lasted from about 2.6 million years ago up to 11,700 years ago. This vast difference in time means that the remains of these two groups of animals would not be deposited in the same strata unless a very unusual geological event had altered the order of the layers, which is improbable but not impossible.