Nannotax3 - ntax_cenozoic - Pletolithus giganteus

Citation: Pletolithus giganteus Cappelli et al 2020

Basionym: Pletolithus giganteus Cappelli et al 2020

Synonyms:

Coccolithus cf. gigas of Bown & Newsam 2017 (this grouping is not mentioned in the formal synonymy of Cappelli et al 2020 but is metioned in the text, p.3)

Distinguishing features:
Parent taxon (Pletolithus): Eocene lineage of large to extremely large Cruciplacolithus-like coccoliths
This taxon: Like C. gigas but cross-bars only slightly rotated (<30°) and so of different lengths

Diagnosis. Very large (> 16 μm) elliptical placoliths with narrow to broad central-area spanned by robust bars that form an asymmetric diagonal cross. Description. Very large coccolithacean with a distal shield consisting of 60–70 elements and an elliptical outline. The tube connecting the two shields is broad and consists of flat elements with complex sutures. The smaller proximal shield is composed of elements with dextral obliquity in proximal view. Specimens belonging to this species show high variability in the width of the central-area, which can occupy from 7% to 13% of the total placolith area. A broad, asymmetric diagonal cross spans the central-area. On the distal side, the bars consist of rectangular plates stacked one on another, whose axes are roughly aligned with the long axes of the bars. On the proximal side, the bars are composed of one row of robust wedge-shaped elements (roughly triangular), nor- mally oriented with the axis of the bar. These elements partially in- terfinger, but do not interfinger along the full length of the wedge. Thickening at the base of the triangular plate is common and it gives rise to a poorly developed depression along the axis of the bar. Under cross-polarized light, thin median extinction lines run along the bars. Differentation. Pletolithus giganteus can be distinguished from other species of the genus by the intermediate orientation of the broad cross bars. Pletolithus giganteus can be differentiated from P. staurion by its large size and wider central-area. Pletolithus giganteus can be dis- tinguished from P. gigas by the diagonally oriented (X-shaped) cross- bars of the latter form. The most diagnostic feature to distinguish consistently between these species is the bar-length ratio. This value is generally > 1.3 in P. giganteus and < 1.3 in P. gigas. Pletolithus gigan- teus can be distinguished from P. mutatus by the more robust cross-bars, their different ultrastructure, and the raised tube cycle.

Geological Range:
Last occurrence (top): within (-Ma, top in "Holocene" stage). Data source:
First occurrence (base): within (-Ma, base in "Holocene" stage). Data source:

References:

Bown, P. R. & Newsam, C. (2017). Calcareous nannofossils from the Eocene North Atlantic Ocean (IODP Expedition 342 Sites U1403–1411). Journal of Nannoplankton Research. 37(1): 25-60. gs O

Cappelli, C., Bown, P. R., Riu, M. D. & Agnini, C. (2020a). Middle Eocene large coccolithaceans: Biostratigraphic implications and paleoclimatic clues. Marine Micropaleontology. 154: 1-17. gs

Pletolithus giganteus

References:

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