Neorylstonia pseudocolumellata ( Beauvais, 1986 )

Vasseur, Raphaël & Lathuilière, Bernard, 2021, Pliensbachian corals from the Western Tethys, Geodiversitas 43 (22), pp. 1187-1291 : 1234-1238

Neorylstonia pseudocolumellata ( Beauvais, 1986)

( Fig. 32 )

TYPE MATERIAL. — Holotype: MNHN.F.R11604 (original designation), Beauvais 1986: 20, pl. 4, fig. 1a-1b; paratypes figured in Beauvais 1986: pl. 4, fig. 1c, d and e. TYPE HORIZON. — Pliensbachian . TYPE LOCALITY. — Beni Tadjit , Morocco.

Mesophyllum pseudocolumellatum Beauvais, 1986: 20 , pl. 4, fig. 1a-1b.

Neorylstonia pseudocolumellata – Vasseur 2018: 259-260, fig. 3.63; Vasseur et al. 2019: 9 -17, fig. 2- 6, 13.6.

STUDIED SAMPLES. — 91 specimens described in Vasseur et al. (2019) (collections MNHN and CPUN).

GEOGRAPHIC AND STRATIGRAPHIC RANGE. — Sinemurian of Amellagou (Jebel Serdrar, High Atlas) and Pliensbachian of Amellagou, Dades Valley, Koudiat Ech Chehem and Taililout (High and Middle Atlas) in Morocco; Pliensbachian of Italy (Caloveto, Calabria).

DESCRIPTION

Solitary coral. Corallum ceratoid, straight or curved. The calice is subcircular in outline. Costosepta straight or slightly curved (possibly post-mortem distortion), free, compact, occasionally rhopaloid. Some first-order septa (S1) rarely reach the axial structure but in most cases the inner edge abruptly dips in the fossa. Lateral faces and distal edge are smooth. No pali. Radial elements are commonly arranged in three distinct size orders with different length and width in transverse sections but S1 and S2 are occasionally indistinct because of similar sizes. In contrast, some other samples show clearly four distinguishable size orders of septa. In the latter case, the first and second size orders geometrically correspond to a subdivision of the S1. Lastly, the S3 are sometimes missing. On the basis of the described arrangement of septal length and thicknesses a very classical model of septal insertion can be proposed, namely 96 septa distributed in five ontogenetical cycles according to 6+6+12+24+48 septa. This model of septal insertion is statistically grounded by univariate statistical analysis in which the number 96 shows a well-marked mode ( Vasseur et al. 2019). Ghosts of septal structures can sometimes be observed in thin sections. They consist in transverse section of a darker axial zone within the septum, a brighter zigzag line or some dark spots in a line considered as remains of “centers of calcification” or centers of rapid accretion ( Stolarski 2003). Growth lines in “ogive” or “gloves fingers” can be seen in longitudinal sections, resulting from the deposition of different successive layers of stereome thickening the septa (thickening deposits of Stolarski 2003). Axial structure present, in the form of a Rugose-like calicular boss made of septa and endotheca. According to Milne Edwards & Haime (1848: 78) and later Berkowski & Weyer (2012) it corresponds to the definition of a pseudocolumella. This pseudocolumella presents different morphologies during the polyp life, giving the fossils a very characteristic aspect in transverse section. It is made of 16 to 26 septa not organized in a strict radial symmetry, more often 21 to 22, organized even in two crescents separated by an axial cavity (type 2) or in the form of a star with opposite septa linked in the calicular axial zone (type 1). Between these two extreme morphologies are some transition states.

In the main cases, hexameral symmetry can be established. The superimposed bilateral symmetry is evidenced by the spatial organization of the axial structure. Endotheca abundant, made of tabular dissepiments regularly arranged in the axial zone. Parathecal wall. Paratheca is continuous with the dissepiments. Synapticulae absent. A true epitheca with growth striae and wrinkles encloses the corallite.

Calicular diameter: 9 to 29 mm – Number of septa: 41 to 104 (mostly 96) – Septal density: 5 to 10 S1 + S2 for 5 mm.

SIMILARITIES AND DIFFERENCES

This taxon is the single case of post-paleozoic coral with a pseudocolumella sensu Berkowski & Weyer (2012) referenced up until now.

Figures

FIG. 32. — Neorylstonia pseudocolumellata (Beauvais, 1986): A: transverse section of the specimen CPUN AM16164, showing a type 2 pseudocolumella with visible pseudocolumellar septa; B: transverse section of the specimen CPUN AM175 showing a type 1 pseudocolumella; C: transverse section in the specimen CPUN DA2905E1.1 showing the true epitheca surrounding the septal apparatus and the stereome deposits on septa; D: detail of the ghosts of septal structure in transverse section (specimen CPUN 2110A2) and the stereome deposits in “ogives” or “glove fingers”;E: longitudinal section of the specimen MNHN.F.A57331-2 showing the endothecal organization in tabular dissepiments and the axial porosity of the pseudocolumella; F, detail of the parathecal wall in continuity with the tabular dissepiments (longitudinal section of the specimen CPUN 2110A2). Scale bars: A, B, E, F, 5 mm; C, 4 mm; D, 2 mm.