Rediscovering <i>Globigerina bollii</i> Cita and Premoli Silva 1960

Abstract

Globigerina bollii Cita and Premoli Silva was described from the historical Langhian-type section in Langhe, Piedmont (Italy). Due to its peculiar compact morphology, it was set apart from all the other globigerinids typical of the coeval Mediterranean fauna, and it was only reported for a short and limited stratigraphic range. The taxon became a first-order marker for the local biostratigraphy with its own Globigerina bollii Zone within the Langhian stage. However, the species was later synonymised with Globigerina falconensis Blow, ending its use in biostratigraphic schemes, and it was no longer utilised by authors working in the Mediterranean area and Paratethys. We present a reassessment of Globigerina bollii, showing for the first time a full collection of high-quality scanning electron and optical microscope images of the type series of specimens and a comparative study with Mediterranean individuals from the Langhian of the Cretaccio Section (Italy) and extra-Mediterranean individuals from Ocean Drilling Program Site 747 in the Kerguelen Plateau (Indian Ocean). The stratigraphic ranges of all the occurrences cited in the scientific literature from 1960 to the present day and all the references including images of the taxon are compiled. We compare G. bollii to other four-chambered morphospecies inhabiting the oceans during the Miocene, providing a detailed discussion of their morphological differences, which allows us to retain G. bollii as a valid taxon and to disclaim its synonymy with Globigerina falconensis. Our taxonomical observations also allow us to reassign Globigerina bollii to the genus Globoturborotalita, due to its strong affinities with other members of that genus, such as G. eolabiacrassata Spezzaferri and Coxall, and G. ouachitaensis (Howe and Wallace). We present a direct visual comparison with the other representatives of middle Miocene globoturborotaliids. An additional comparison is also discussed with Globigerina bollii lentiana Rögl, a species endemic in the Paratethys. We conclude that the presence of G. bollii in the Mediterranean Basin during such a confined stratigraphic interval (Mediterranean Subzone MMi4c–MMi4d), might be a palaeogeographical indicator of the intermittent opening of the eastern gateway with the Paratethys, affecting the Mediterranean faunas during the Langhian and their migration from oceanic realms into the Paratethys and Mediterranean.