Taxonomic evaluation of various morphological characters in the Late Cretaceous desmoceratine polyphyletic genus Damesites from the Yezo Group in Hokkaido and Sakhalin

Intra- and interspecific variation and ontogenetic changes in various shell characters of the Late Cretaceous desmoceratine ammonoid Damesites are described, and their taxonomic implications are discussed based on specimens from the Cretaceous Yezo Group in Hokkaido and Sakhalin. Our study reveals that many diagnostic features (e. g., appearance of longitudinal striations, height of ribbing, regularity of ribbing as well as constriction curvature) and early internal shell structures, are in fact inappropriate as diagnostic features of Damesaes morphotypes. In contrast, ontogenetic changes in shell ornament, curvature of growth lines and whorl expansion ratio are herein demonstrated to be key characters for species recognition and reconstructing the phylogenetic relationships of the taxa of the subfamily Desmoceratinae. Based on these results, previously described Damesites species from the uppermost Turonian-lower Campanian interval should be reclassified into three groups. Damesites damesi, D. damesi intermedius, D. semicostatus, and D. laticarinatus are assigned to the first group. D. ainuanus and Damesites sp. are assigned to the second group. D. stigma from the Vezo Group represents the third group. Furthermore, analysis of ontogenetic changes in shell ornament, curvature of growth lines, and whorl expansion ratio suggests that the second and third groups together belong to a different evolutionary lineage from the first group.