In this study, carbonate compounds within samples taken from seasonal layers, which constitute the skeleton of belemnites from the Cretaceous age, were examined. The distribution of Mg, Mn, Fe, Cu, and Sr in these layers which formed during the ontogenetical formation of belemnites were examined through the skeletons of Neohibolites and Belemnitella species. The taxonomical relationships between individuals belonging to the same and different species and phyllogenetical branches were examined within the context of the concentration of these elements, and it was found that the different taxons have different element contents. It was found that these differences become greater as the duration between the taxons increases. In other words, as the taxonomy changes from individuals to species and from species to families, the morphological differences as well as the chemical differences become greater. Thus, it can be stated that the distribution of elements within belemnites skeletons has certain implications with respect to taxonomical considerations. The layers forming the shells of belemnites are distinguished by different color scales. These layers, with different tonnes of dark and light colors, are of alternating character which depend upon the physical variability, temporal continuity and the intensity of the paleogeographical habitat. The occurrence of different tones is related to the amount of organic matter and clay content. The different colors of the layers could also be used for determining the ages of belemnites.