Taxonomy of Late Jurassic - Early Cretaceous aptychi from Bulgaria

Abstract

This paper presents the taxonomic revision of Late Jurassic and Early Cretaceous aptychi housed at the National Museum of Natural History, Sofia (Bulgaria). The aptychi came from the pelagic, flysch-like and flysch deposits of Central and North Bulgaria, and most of them have been initially described by StefaNoV (1961). The taxonomic revision has led to the determination of 23 species and subspecies of six genera. A new species named Mortilletilamellaptychus stefanovi is described. The collection contains also the holotype of Didayilamellaptychus filicostatus (StefaNoV), which was previously elevated from a variety to species level by MěchoVa et al. (2010). A valve of Didayilamellaptychus cf. didayi preserved in the body chamber of a Neolissoceras supports the hypothesis that lamellaptychi and perhaps punctaptychi belong to the natural system of ammonites of family Haploceratidae ZIttel, 1884. It became evident that the state of preservation may strongly affect the taxonomic determination of the aptychi. Only in exceptional cases (occurrence of both valves in a pair with different state of preservation) this preservation phenomenon can be revealed and erroneous determination of any of the valves could be possibly avoided.