Sphenolithus quadricornutus Steurbaut & Nolf, 2021, n. sp.
Creators: name: Steurbaut, Etienne
name: Nolf, Dirk
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Chromista
Haptophyta
Coccolithophyceae
Discoasterales
Sphenolithaceae
Sphenolithus
Sphenolithus quadricornutus

description: Sphenolithus quadricornutus n. sp.
(Fig. 20 N-Q)
urn:lsid:zoobank.org:act: 129C12D5-F3FE-47C6-849A-EE69215A1E64
HOLOTYPE. — Fig. 20N (IRSNB b7154) (negatives stored in the collections of the RBINS).
PARATYPES. — 3 figured specimens (h without spines = 3.8-4.8 µm): 1 from the Lede Sand Formation, at Balegem (Fig. 20O) (IRSNB b7155) and 2 from Mont-des-Récollets: 1 from the Lede Sand Formation (Fig. 20P) (IRSNB b7156) and 1 from the Brussel Sand Formation (Unit B4) (Fig. 20Q) (IRSNB b7157).
DIAGNOSIS. — Small hourglass-shaped sphenoliths, consisting of a conical proximal column, surmounted by a series of blocky distally widening lateral elements, both of almost equal height, supporting four equally spread diverging spines.
DERIVATIO NOMINIS. — Refers to the four conspicuous diverging spines which rise from the corners of the sphenolith.
LOCUS TYPICUS. — Mont-des-Récollets, ‘ Grande Carrière’, N France; 50°48’02.74”N, 2°30’23.06”E.
STRATUM TYPICUM. — Lede Sand Formation (sample 126.50 m); lower part of NP15.
DIMENSIONS. — Height = 11.2 to 12.8 µm with spine; Height body, without spine = 5 to 6.5 µm; Maximum width (wmab) = 4.4-5.2 µm (holotype: htotal = 11.2 µm, hpp = 2.5 µm, hle = 2.5 µm, hds = 6.2 µm; wpp = 3.4 µm).
DISTRIBUTION. — This species has a rather restricted range. It occurs in the top of the Brussel Sand Formation (Unit B4) and in the Lede Sand Formation at Mont-des-Récollets, and in several outcrops of the Lede Sand Formation (Balegem, Oosterzele) and the base of the overlying Wemmel Sand Member (Oedelem borehole). Its range seems thus to be restricted to the top of NP14 and lower NP15.
DESCRIPTION
These sphenoliths are very tiny, consisting of a conical proximal column and a series of blocky lateral elements, which seem to widen distally, producing the typical hourglass shape. The latter is also easily observed in cross polarized light (see discussion below). Both the proximal column and the area with the lateral elements are of almost equal height (each c. 2.5 µm). Half long diverging spines (maximum 1.5 times as long as the sphenolith’s body) emerge from each of the four corners.
DISCUSSION
Sphenolithus quadricornutus n. sp. bears a striking resemblance to Sphenolithus quadrispinatus, described from the Late Miocene (Tortonian, NN10) of the southern Atlantic (Perch-Nielsen 1980), especially in its dimensions and the length and the position of the spines. They essentially differ in general outline, which is cylindrical in S. quadrispinatus, but hourglass-shaped in S. quadricornutus n. sp. This is also clearly observed in cross-polarized light when seen at 0°. In this position S. quadrispinatus is highly birefringent, consisting of four almost equal rectangular blocks (height is greater than width), separated by extinction lines with cross pattern. S. quadricornutus n. sp. is also strongly birefringent in that position, but presents an x-shaped interference figure, of which the four bright parts are rather rhombic instead of rectangular and separated by extinction lines with cross pattern. Viewed at 45° this cross pattern turns into an x-pattern.
description: Published as part of Steurbaut, Etienne & Nolf, Dirk, 2021, The Mont-des-Récollets section (N France): a key site for the Ypresian-Lutetian transition at mid-latitudes - reassessment of the boundary criterion for the base- Lutetian GSSP, pp. 311-363 in Geodiversitas 43 (11) on page 352, DOI: 10.5252/geodiversitas2021v43a11, http://zenodo.org/record/4891107