Variation analysis of ammonites and conodonts (implementing geographic information systems): A qualitative and quantitative method

Geographic Information Systems (GIS) has been utilized to investigate a pattern matching technique of analyzing shape variation on paleontological material. Two different fossil groups for which the taxonomy has been based on subjective interpretation of complex morphological shapes were included in this research: Cretaceous ammonoids and Devonian conodonts. The shape and complexity of sutures, gross conch morphology, and conch ornamentation are considered to be important taxonomic characters for Cretaceous ammonoids. These features are widely used in the taxonomy of ammonoids and form the basis for interpretation of phylogenetic histories. Because of the complexity of ammonoids sutures, they are traditionally simply compared visually. The GIS technique allowed for a more objective and precise method for description and comparison of ammonoids suture patterns, as well as conch shape and ornamentation. Analysis of these features using the method of least squares was used to determine the best-fit line, and coefficients of determination (R-square) values were calculated to evaluate the significance of any correlations between sutural measurements and shell morphology. In addition, each of the suture measurements was plotted against the other. The best-fit linear relationship was determined through least squares regression, and coefficients of determination were calculated. There is substantial variation in shell and sutural morphology found among these Coilopoceras springeri specimens. Variation in sutural morphology is gradational and only weakly tied to shell morphology. Variation in sutural morphology appears to have been relatively disjunct from variation in shell morphology. Species of the conodont genus Palmatolepis are the primary means for recognizing and correlating the subdivisions of the Late Devonian. The subtle differences in the shape of P1 (platform) elements make reliable discrimination of the species possible only by relatively few experts. GIS integrated with discriminate function analysis has been used to qualitatively and quantitatively analyze shapes and outlines of P1 elements for characterization of Frasnian Palmatolepis species. Discriminate function analysis shows reliable statistically significant differences between the species examined. The analysis yields clearly defined morphological characters and establishes shape-diagnostic criteria for ease in identification. This method confirms Klapper’s & Foster’s (1986, 1993) species identification of the Palmatolepids used in this study.