Fossils

In its modern sense, paleontology is an interdisciplinary branch of the natural sciences that studies organisms that lived in the geological past and their living environments. It encompasses several research areas, including fossilization processes, paleoecology, biostratigraphy, and paleobiogeography, all closely linked to past climatic and environmental changes. Systematic paleontology, in particular, focuses on the description, classification, and taxonomy of fossils, as well as their phylogenetic relationships with extant forms.

The primary object of study in paleontology is the fossil, defined as any part of an organism preserved over time through chemical and mineral processes. Fossilization mainly affects structures that were already partially mineralized during the organism’s life, such as bones, teeth, shells, and exoskeletons, making these fossils the most commonly encountered in paleontological studies. Among these, shelled mollusks are particularly well represented. Despite the relative rarity of complete preservation due to erosion and compression, fossils are fundamental tools for reconstructing the general patterns of life’s evolution and for supporting phylogenetic relationships among species.

In geology, stratigraphy studies the layering and dating of rocks, as well as the relationships between distinct lithological units, with particular emphasis on sedimentary rocks. The fundamental geological principle of stratigraphy is the law of superposition, according to which, in sedimentary successions, lower layers are older than those above them, reflecting the sequential accumulation of sediments. This principle is fully applicable to marine environments, which are of particular interest in this field.

Rock dating can be performed using various physical, chemical, or paleontological methods, each with its limitations. For this reason, whenever possible, results obtained through different approaches are compared to reduce chronological uncertainty. A chronostratigraphic unit comprises the set of rocks formed within a given time interval, while the interval itself is defined as a geochronological unit. These units are organized hierarchically according to standardized categories: age, epoch, period, era, and eon, in order of increasing duration.

The geologic time scale (geochronological scale) represents the division of time from the formation of the Earth to the present and is widely accepted by the international scientific community. The International Commission on Stratigraphy (ICS) is the body responsible for formalizing the scale and its nomenclature. The United States Geological Survey (USGS) has produced a color-coded version of the scale, assigning a conventional color to each age; although not universally adopted, this version is better organized and more detailed and will be the one in part used in this project.

According to USGS conventions, the designations “upper,” “middle,” and “lower” apply to rocks, whereas “early,” “middle,” and “late” refer to time. Since geologic time units are used globally, they may have different names depending on the characteristic fossils, so the same time interval can be referred to by different names in different regions. Standardizing chronostratigraphic terminology and defining universal horizons are central tasks of the ICS; therefore, the nomenclature and chronological boundaries of each period may be subject to revision.

Regarding the chronostratigraphic subdivision of the Cypraeidae, from the appearance of the oldest species to the present, the relevant periods are as follows:

* ID = Interval and (duration) on million of year (ma)

Dates and subdivisions are based on the International Chronostratigraphic Chart 2023 of the International Commission on Stratigraphy (ICS) and USGS resources.