You may find it useful for the clear definitions, and for excellent links on a variety of topic. The creature, named Mystacodon selenensis, is the oldest baleen-whale relative yet found.
Man made intrusions and activity in the archaeological record need not form chronologically from top to bottom or be deformed from the horizontal as natural strata are by equivalent processes.
Some archaeological strata (often termed as contexts or layers) are created by undercutting previous strata.
This usually requires what is commonly known as a "dating method".
Several dating methods exist, depending on different criteria and techniques, and some very well known examples of disciplines using such techniques are, for example, history, archaeology, geology, paleontology, astronomy and even forensic science, since in the latter it is sometimes necessary to investigate the moment in the past in which the death of a cadaver occurred.
They include the appearance of the earliest baleen whale ancestors.