Early Maastrichtian ammonites and nautiloids from Hrebenne, southeast Poland, and phenotypic plasticity of Acanthoscaphites tridens (Kner, 1848): A commentary

A recent attempt by Kin (2010, Cretaceous Research 31, 27–60) to reject dimorphism of a giant, early Maastrichtian scaphitid ammonite Acanthoscaphites tridens is not substantiated by the data presented by this author, which are of poor quality, and thus inadequate for testing biological hypotheses. Six “phenomorphic” classes proposed by Kin for the material of A. tridens from Hrebenne and other European localities, are purely typologic, arbitrary categories of no biological significance. Moreover, these categories are inadequately defined, even as for typologic standards. In contrast, a combination of size, relative height of the body chamber, shape of the umbilicus, and extent of the ventrolateral and ventral tubercles in the conchs of mature individuals of A. tridens, allows for a reliable discrimination of merely two natural classes in samples of this species. These classes may be referred to as microconchs and macroconchs, in full accordance with the views of earlier authors.