Olcostephanidae (Ammonoidea) from the upper Valanginian Taraises Formation (Durango State, Mexico)

In this work we study Hoplites symonensis Bِse, 1923 which was previously assigned to various species, some of which were considered as new taxa. Bِse defined two taxa using the specific name of symonensis which can be assigned to the genus Olcostephanus. In order to avoid problems of homonymy we reviewed both Astieria symonensis and Hoplites symonensis. We synonymize Astieria symonensis with the older species Olcostephanus potosinus (Castillo and Aguilera, 1895) and reassign the species Hoplites symonensis as an Olcostephanus (Olcostephanus) symonensis. Additionally, we also erect a new species, Olcostephanus (Olcostephanus) cuencamensis sp. nov. This taxonomic update is part of an ongoing project to properly review the upper Valanginian ammonoids of the Taraises Formation in northern Mexico, previously studied by other authors. In this work we conform to the idea that the Family Olcostephanidae has a high Mexican endemic character, as previously suggested by other authors. The upper Valanginian ammonites studied herein come from a section of the Taraises Formation from the Cuencamé area, Durango State. The bed-by-bed sampling was a useful tool for the precise biostratigraphic location of the identified taxa.