A model of reconstruction for the oral apparatus of the Ordovician conodont genus Protopanderodus Lindström, 1971

Abstract

Elements of the Ordovician conodont genus Protopanderodus have been investigated in order to provide a model of reconstruction for its oral apparatus. In total, 4,202 elements from the five named species representing this genus in the Swedish Middle Ordovician are included in this study: P. rectus, P. parvibasis, P. graeai, P. robustus and P. calceatus. The well-preserved specimens were studied in detail for identification of distinct element types and calculations were made to determine element ratios and minimum number of elements in a single apparatus. Three element groups, M, S and P, were recognised for all five species and their relative ratio is indicative of apparatuses consisting of at least 21 elements. However, the number of element types and their distribution varies between the species. The four bicostate species, P. rectus, P. parvibasis, P. graeai and P. robustus, have similar morphological characters and are believed to belong to the same evolutionary lineage. They possessed apparatuses consisting of M, Sa, Sb1, Sb2, Sc, Pa and Pb elements. By contrast, the multicostate species P. calceatus is morphologically different and had an apparatus consisting of M1, M2, Sa, Sb, Sc, “Sd”, Pa, Pb1 and Pb2 elements. These differences indicate that P. calceatus is not so closely related to the other species, possibly representing a separate evolutionary lineage, and may warrant an exclusive generic assignment.