The methods developed can be used to model and compare ammonitic suture patterns. Using the GIS system for visually and quantitatively matching ammonitic sutures has been demonstrated as an effective way to classify ammonites. A few suggestions are worth noting. The holotype should be used as the guide in making a template because the holotype is the specimen designated as the nomenclatural type in describing a new species and is the model against which other specimens are compared. By reversing the left template and overlaying it on the right, one produces the best-fit template (Figure 4.1). With the small number of actual published suture patterns, combining right and left patterns is the best method for attaining the most accurate template. The control points may be placed logically at the junction of the sutural elements, i.e., ventral, lateral, and umbilical beginnings and endings. Slight variation in the location of the tie points does not affect the results.
Investigating the differences between suture patterns is straightforward using GIS, as calculated suture lengths can be used for comparison. As seen in Figure 5.1, there is a definite difference between right and left suture patterns, with the right patterns being shorter in the ventral to dorsal length aspect. The difference when comparing the left and right sutural templates is 13.15 units. The shell measurement data shows that the right umbilical diameters are larger than the left umbilical diameters for all specimens (Manship 2003). A wider umbilicus on the right would support the fact that the sutures on the right would be shorter than those on the left; the opposite would be true for the left side. This right and left sutural difference is found in all Coilopoceratidae specimens from all localities and is not likely to be a result of compaction or other post-burial deformation.
With the GIS method, sutures can also be easily compared using the area of mismatch. Table 2 shows the comparisons between individual sutures. Quantitative measures of difference in area were seen and as expected, the difference is low for opposing sutures and continually increases from comparison of the same species, to the sutures of two different species, and the largest difference is between two different genera.
The fit of a suture pattern to a template can also be quantified by calculating the percentage of line that falls outside the template. Table 3 shows a quantitative comparison between the percent of suture length that lies outside of each template. As seen in Table 3, Coilopoceras springeri sutures fit best in the Coilopoceras springeri right/left template. The templates that were made with less than six sutures showed a higher percentage of suture length outside of the template's boundary. A much higher percentage of suture length outside of the template boundary is seen when comparing any suture to the Hoplitoides sandovalensis right template, made with only three sutures, in contrast to a much lower percentage of suture length outside of the Coilopoceras springeri right/left templates made using 10 suture patterns. This method, then, works best when all templates are made with a comparable number of sutures, ideally at least six. Otherwise, tested sutures may fit best in whatever template has the most sutures. With limited published sources of suture patterns, it may be difficult to acquire enough suture patterns to make an accurate sutural template. For the most complete and precise template, museum collection resources should be thoroughly investigated.
Simpler sutures also are more likely to fit within multiple templates, which is why juvenile sutures are not a good choice. Even the relatively straight suture pattern of nautiloids could be made to fit within an ammonite template. For the best possible use of the template model for classification, only well-developed adult sutures should be used, and placement of the elements should be carefully noted.
The objective of this study was to assign ammonite specimens to species by use of a sutural template. The best approach is to combine visual examination of sutures and templates with these percentages to make the strongest case when classifying ammonites. The majority of all tested specimens correlated with their correct templates and do not fall within the templates of other species. All of the specimens from my field locality proved to be Coilopoceras springeri.