Time to say goodbye: taxonomic revision of Dictyoconus walnutensis (Carsey, 1926), the last Lower Cretaceous representative of the genus

ABSTRACT

Dictyoconus walnutensis: (Carsey) represents a middle-lower upper Albian orbitolinid marker taxon, endemic to the American-Caribbean realm (Gulf Coast area, Mexico, Venezuela). The species has a number of features incompatible with Dictyoconus Blanckenhorn, namely the presence of a simple and slightly eccentric embryo instead of an initial spire with an embryo that may be septulated, lack of marginal apertures, and a rather simple exoskeleton. Based on the combination of these characteristics, the new genus Carseyella is herein established with the new combination Carseyella walnutensis (Carsey). The upper Aptian Carseyella algeriana (Cherchi & Schroeder) comb. nov. is considered a more primitive representative due to the lack of horizontal partitions in the marginal zone. Dictyoconus once used as a catch-all term for various larger foraminifera of Jurassic to Palaeogene age is now removed from the Early Cretaceous and restricted to the Maastrichtian – Palaeogene. The phylogenetic relationship of the Maastrichtian (D. bakhtiari Schlagintweit, Rashidi & Babadipour) and the Eocene species [e.g., D. egyptiensis (Chapman), D. indicus Davies] requires further clarification. This once commonly used generic name can now be used in a much more precise and stratigraphically restricted sense.

KEYWORDS:

• Orbitolinidae
• dictyoconus
• taxonomic revision
• phylogeny
• lower Cretaceous

Acknowledgments

Many thanks to Liath Appleton (Austin), collections manager of the Non-vertebrate Paleontology collections at the University of Texas, Jackson School Museum of Earth History for providing the two images (illustrated in Davies 1939) catalog numbers BEG00036454.000 and BEG00036455.000 and the permission for illustration. Koorosh Rashidi (Yazd) and Elham Nafarieh (Tehran) are thanked for providing the images of Dictyoconus from the Maastrichtian and Eocene of Iran. Robert Scott (Cleveland) provided the images from the Edwards Limestone of Texas and Karl Krainer (Innsbruck) from the Finlay Formation of New Mexico. I am also grateful to Françoise Le Coze (Saint-Étienne) and Marius (Dan) Georgescu (Calgary) for general discussion and assistance with the English language. The two reviewers Robert W. Scott (Cleveland) and Simon Mitchell (Kingston) provided helpful comments.

Disclosure statement

No potential conflict of interest was reported by the author.