ADDRESSING INCOMPLETE SPECIMENS OF TURRITELLINE GASTROPODS: THE THEORETICAL APEX SYSTEM

Investigators working with high-spired gastropod shells are often challenged by having to examine broken specimens. Therefore, many studies elect to consider only complete specimens. However, utilizing only complete specimens has inherent limitations. For example, data may be skewed as only intact shells were chosen for data retrieval. Here, we present a new approach—the Theoretical Apex System (TAS)—which identifies a hypothetical apex normalized to apical angle, thus allowing data to be generated and compared for both complete and incomplete specimens.

This study generated theoretical apical angles for nine fossil species of turritelline gastropods (Family Turritellidae, Subfamily Turritellinae) from the Plio-Pleistocene of Florida and North Carolina. The standard deviation of these angles ranged from 0.7 to 2.3 degrees. The system was also used to generate the additional hypothetical shell length lost from the apical end of a specimen, which averaged 34% (range 9% to 68%). Using the TAS, this study was also able to compare drill hole location and size on these broken specimens. When measurements of all nine species were considered the data suggested a relationship between outer bore hole diameter and increasing distance from the theoretical apex. Using the TAS in this study uniquely allowed for the normalization of data on incomplete specimens and the comparison of this data to other studies on complete specimens. Additionally, the TAS provided an improved method to measure apical angles on all specimens regardless of completeness.

The TAS has many applications for studies in areas such as taphonomy, morphometrics, predation, and sclerochronology. Future work will include a statistical evaluation of data gathered using the TAS, in addition to examining breakage location for critical points, and a three dimensional model that will give users a more complete picture of incomplete specimens.