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Nannoceratopsis symmetrica
Nannoceratopsis symmetrica Bucefalo Palliani and Riding, 2000, p.12, figs.6I–P,7J.
Holotype: Bucefalo Palliani and Riding, 2000, fig.6I.
Age: early Toarcian.
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Original description: [Bucefalo Palliani and Riding, 2000, p. 12]:
Nannoceratopsis symmetrica sp. nov. (Figs 6I-6P; 7J)
Holotype. Specimen MPK 10823, sample MPA 16839, Brown Moor Borehole, North Yorkshire, core depth 171.39 m (Fig. 6I).
Repository. Collections of the Basin Analysis and Stratigraphy Group, British Geological Survey, Nottingham, U.K.
Type locality. Brown Moor Borehole, near Acklam, North Yorkshire, U.K. (NGR SE 8126 6203).
Stratigraphical horizon. Mulgrave Shale Member, Whitby Mudstone Formation, Lower Toarcian, H. falciferum Ammonite Zone, H. exaratum Ammonite Subzone, 171.39 m (Appendix 1).
Derivation of name. The specific name is derived from the virtually perfectly symmetrical outline of this form in lateral view about the longitudinal axis.
Diagnosis. A globose and subspherical species of Nannoceratopsis, having two bulbous antapical horns which are distally pointed and of similar size. Within a population, the antapical horns are of variable length, hence imparting subtly differing morphologies to the antapical area. The autophragm is thin and shagreenate to microscabrate.
Description. Nannoceratopsis symmetrica sp. nov. is a distinctly subspherical species of this genus, which is globose in lateral view. The maximum width of this species is located in mid-lateral position on the hypocyst. The hypocyst is characterized by two bulbous antapical horns of virtually identical size and shape, which have sharply -pointed distal terminations. The horns may be of variable length, varying from 11 μm
(Fig. 6O) to 3.5 μm (Fig. 6K). The variable length of the horns imparts an equally varied morphology to the antapical region. The mid lateral area of the antapex may be either concave (Fig. 6J), slightly centrally convex (Fig. 6K) or flattened (Fig. 6M). The autophragm is thin; the surface has extremely low-relief ornamentation and is shagreenate to microscabrate. The sagittal band is not thickened and the paracingulum is normally well developed.
Dimensions (in μm).
Minimum (Mean) Maximum
Overall length of cyst 45 (48) 53
Overall width of cyst 36 (42) 46
20 specimens measured
Comparison. Nannoceratopsis symmetrica sp. nov. differs from Nannoceratopsis deflandrei subsp. senex and Nannoceratopsis magnicornus because the latter two are characterized by a prominent single hypocystal horn. It also differs from Nannoceratopsis ridingii and Nannoceratopsis triceras in having two, as opposed to three, hypocystal horns. This new species may be distinguished from Nannoceratopsis evae Prauss, 1989, which is entirely devoid of horns. The sagittal band of Nannoceratopsis symmetrica sp. nov. is not differentiated or thickened, like the species Nannoceratopsis ambonis Drugg, 1978 and Nannoceratopsis dictyambonis Riding, 1984. Several species of Nannoceratopsis have markedly reduced ventral antapical horns; these comprise Nannoceratopsis deflandrei subsp. deflandrei Evitt, 1961, N. gracilis Alberti, 1961, N. plegas Drugg, 1978 and N. triangulata Prauss, 1987. The large, distally well-rounded hypocystal horns of Nannoceratopsis globiformis Bucefalo Palliani and Riding, 1998 distinguish this form from Nannoceratopsis symmetrica sp. nov. The deep antapical concavities of N. pellucida Deflandre, 1938, N. radiata Kumar, 1986 and N. spiculata Stover, 1966 allow immediate differentiation from
this new species; furthermore, N. spiculata is antapically cavate. Nannoceratopsis raunsgaardii Poulsen, 1996 has a distinctly triangular outline in lateral view and the maximum lateral width is at the antapex. Bucefalo Palliani & Riding (1998, fig. 9), gave sketch diagrams of all validly formalized species of Nannoceratopsis published at that time.
Stratigraphical distribution. Nannoceratopsis symmetrica sp. nov. was recorded in the Lower Toarcian (D. tenuicostatum and H. falciferum Ammonite zones) in the Brown Moor Borehole (Fig. 3). It was also observed in the Lower Toarcian (D. tenuicostatum and H. falciferum Ammonite zones) in the Yorkshire coastal outcrops (Fig. 4).
Holotype: Bucefalo Palliani and Riding, 2000, fig.6I.
Age: early Toarcian.
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Original description: [Bucefalo Palliani and Riding, 2000, p. 12]:
Nannoceratopsis symmetrica sp. nov. (Figs 6I-6P; 7J)
Holotype. Specimen MPK 10823, sample MPA 16839, Brown Moor Borehole, North Yorkshire, core depth 171.39 m (Fig. 6I).
Repository. Collections of the Basin Analysis and Stratigraphy Group, British Geological Survey, Nottingham, U.K.
Type locality. Brown Moor Borehole, near Acklam, North Yorkshire, U.K. (NGR SE 8126 6203).
Stratigraphical horizon. Mulgrave Shale Member, Whitby Mudstone Formation, Lower Toarcian, H. falciferum Ammonite Zone, H. exaratum Ammonite Subzone, 171.39 m (Appendix 1).
Derivation of name. The specific name is derived from the virtually perfectly symmetrical outline of this form in lateral view about the longitudinal axis.
Diagnosis. A globose and subspherical species of Nannoceratopsis, having two bulbous antapical horns which are distally pointed and of similar size. Within a population, the antapical horns are of variable length, hence imparting subtly differing morphologies to the antapical area. The autophragm is thin and shagreenate to microscabrate.
Description. Nannoceratopsis symmetrica sp. nov. is a distinctly subspherical species of this genus, which is globose in lateral view. The maximum width of this species is located in mid-lateral position on the hypocyst. The hypocyst is characterized by two bulbous antapical horns of virtually identical size and shape, which have sharply -pointed distal terminations. The horns may be of variable length, varying from 11 μm
(Fig. 6O) to 3.5 μm (Fig. 6K). The variable length of the horns imparts an equally varied morphology to the antapical region. The mid lateral area of the antapex may be either concave (Fig. 6J), slightly centrally convex (Fig. 6K) or flattened (Fig. 6M). The autophragm is thin; the surface has extremely low-relief ornamentation and is shagreenate to microscabrate. The sagittal band is not thickened and the paracingulum is normally well developed.
Dimensions (in μm).
Minimum (Mean) Maximum
Overall length of cyst 45 (48) 53
Overall width of cyst 36 (42) 46
20 specimens measured
Comparison. Nannoceratopsis symmetrica sp. nov. differs from Nannoceratopsis deflandrei subsp. senex and Nannoceratopsis magnicornus because the latter two are characterized by a prominent single hypocystal horn. It also differs from Nannoceratopsis ridingii and Nannoceratopsis triceras in having two, as opposed to three, hypocystal horns. This new species may be distinguished from Nannoceratopsis evae Prauss, 1989, which is entirely devoid of horns. The sagittal band of Nannoceratopsis symmetrica sp. nov. is not differentiated or thickened, like the species Nannoceratopsis ambonis Drugg, 1978 and Nannoceratopsis dictyambonis Riding, 1984. Several species of Nannoceratopsis have markedly reduced ventral antapical horns; these comprise Nannoceratopsis deflandrei subsp. deflandrei Evitt, 1961, N. gracilis Alberti, 1961, N. plegas Drugg, 1978 and N. triangulata Prauss, 1987. The large, distally well-rounded hypocystal horns of Nannoceratopsis globiformis Bucefalo Palliani and Riding, 1998 distinguish this form from Nannoceratopsis symmetrica sp. nov. The deep antapical concavities of N. pellucida Deflandre, 1938, N. radiata Kumar, 1986 and N. spiculata Stover, 1966 allow immediate differentiation from
this new species; furthermore, N. spiculata is antapically cavate. Nannoceratopsis raunsgaardii Poulsen, 1996 has a distinctly triangular outline in lateral view and the maximum lateral width is at the antapex. Bucefalo Palliani & Riding (1998, fig. 9), gave sketch diagrams of all validly formalized species of Nannoceratopsis published at that time.
Stratigraphical distribution. Nannoceratopsis symmetrica sp. nov. was recorded in the Lower Toarcian (D. tenuicostatum and H. falciferum Ammonite zones) in the Brown Moor Borehole (Fig. 3). It was also observed in the Lower Toarcian (D. tenuicostatum and H. falciferum Ammonite zones) in the Yorkshire coastal outcrops (Fig. 4).