This area of study forms the foundation of the geologic time scale and is one of the primary ways to temporally correlate stratigraphic sections (locally, regionally, and globally). More specifically, biostratigraphy is the practice of using an assemblage of fossil within a stratigraphic section to establish a relative temporal relationship or ‘zone’ with which once can compare on a regional and/or global scale. Although many different types of fossils are commonly used, ammonites, conodonts, and bivalves stand-out as preeminent groups with which to denote zone (and sub-zone) level constraint throughout much of the early to middle Mesozoic. To help illustrate this, Figures 1 and 2 (next page) show schematic diagrams illustrating the basis for biozone definitions based on ammonite occurrences within a hypothetical stratigraphic section.