On some Rarecostites (Parkinsoniidae, Ammonoidea) from the Upper Bajocian Parkinsoni zone of the Northern Caucasus

Abstract

The ammonites of the genus Rarecostites (subfamily Parkinsoniinae) are studied from the lower part of the Upper Bajocian Parkinsonia parkinsoni Zone of the Kyafar River (Bolshoi Zelenchuk River Basin, Karachai-Cherkessia, Russia). The locality contains numerous microconch shells of R. subarietis (Wetzel). We follow de Grossouvre (1919) in considering the names R. acris (Wetzel) and R. arietis (Wetzel) to be subjective synonyms of R. subarietis and, thus, the standard Acris should be replaced by the Subarietis Subzone. The lower part of the section also contains numerous microconchs of R. sherstyukovi sp. nov. and, less commonly, macroconchs of R. kyafarensis sp. nov. The phylogeny of Rarecostites species is reconstructed; the above species are described and figured and the sherstyukovi and subarietis faunal horizons are established.