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Abstract
Abstract. We present a taxonomic revision of the family Fasciculithaceae focused on forms that characterize the early evolution of this family group, which are currently included within the genera Gomphiolithus, Diantholitha, Lithoptychius and Fasciculithus. The investigation approach is based on a combined light microscope (LM) and scanning electron microscope (SEM) analysis of specimens from well-preserved ODP–DSDP site material (ODP Site 1209; Site 1262; ODP Site 1267; DSDP Site 356; DSDP Site 119) and outcrops (Bottaccione and Contessa, Italy; Qreiya, Egypt) across the Danian–Selandian transition. The direct LM–SEM comparison of the same individual specimen provides clarification of several taxa that were previously described only with the LM. One new genus (Tectulithus), five new combinations (Tectulithus janii, Tectulithus merloti, Tectulithus pileatus, Tectulithus stegastos and Tectulithus stonehengei) and six new species are defined (Diantholitha pilula, Diantholitha toquea, Lithoptychius galeottii, Lithoptychius maioranoae, Tectulithus pagodiformis and Fasciculithus realeae). The main characteristics useful to identify fasciculiths with the LM are provided, together with a 3D–2D drawing showing the main structural features. The accurate taxonomic characterization grants the development of an evolutionary lineage that documents a great fasciculith diversification during the late Danian and early Selandian. Four different well-constrained events have been documented: the lowest occurrence (LO) of Gomphiolithus, the paracme of Fasciculithaceae at the top of Chron C27r (PTC27r), the radiation of Diantholitha (LO Diantholitha), the paracme of Fasciculithaceae at the base of Chron C26r (PBC26r), the radiation of Lithoptychius (LO Lithoptychius) and the radiation of Tectulithus (lowest common occurrence of Tectulithus) that shows the biostratigraphic relevance of this group across the Danian–Selandian transition.
Highlights
During the early Paleocene, radiation of planktonic communities took place and many new genera of calcareous nannofossils evolved, including the appearance of a new morphostructural group in the order Discoasterales (Hay, 1977) consisting of biantholiths, fasciculiths and sphenoliths
The investigation approach is based on a combined light microscope (LM) and scanning electron microscope (SEM) analysis of specimens from well-preserved ODP–DSDP site material (ODP Site 1209; Site 1262; ODP Site 1267; DSDP Site 356; DSDP Site 119) and outcrops (Bottaccione and Contessa, Italy; Qreiya, Egypt) across the Danian–Selandian transition
The evolution of the family Fasciculithaceae in the upper Danian–lower Selandian resulted in a wide range of morphologies as a result of successive and rapid diversification events through time
Summary
During the early Paleocene, radiation of planktonic communities took place and many new genera of calcareous nannofossils evolved, including the appearance of a new morphostructural group in the order Discoasterales (Hay, 1977) consisting of biantholiths, fasciculiths and sphenoliths. In addition to the emendation of the genus Fasciculithus, three new genera were introduced by Aubry et al (2011): Gomphiolithus, Diantholitha and Lithoptychius These new genera include new species as well as numerous forms that were previously classified as Fasciculithus, distinguished by the presence or absence of structural units such as the column, the collaret, the calyptra and the central body. The origin of these nannoliths remains uncertain and the postulated hypotheses suggested a phylogenetic relationship with either Markalius inversus
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