In a certain area of undisturbed layers of rock, fossils of horseshoe crabs may be found in the upper layer, and a lower layer contains fossils of trilobites. trilobites are extinct aquatic arthropods resembling modern horseshoe crabs. this information suggests that

The above information suggests that trilobites are older than horseshoe crabs because they are found in a layer below the crabs and the rocks have been proved to be undisturbed. This satisfies the Law of Superposition. The fact that the horseshoe crabs are found in a younger layer than trilobites and that they resemble each other suggests that horseshoe crabs could have evolved from trilobites. 

~potters6/te801/biology/biounits/respiration.htm