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Nannoceratopsis spinosa
Nannoceratopsis spinosa Riding and Helby, 2001a, p.13–14, figs.7A–F,I.
Holotype: Riding and Helby, 2001a, fig.7I.
Age: early Toarcian.
Original description (Riding & Helby, 2001a):
Description. An acavate, relatively elongate species of Nannoceratopsis, intermediate in size and having two prominent, distally tapering, antapical horns of essentially similar size. The horns are distally pointed or rounded. The antapex is consistently markedly concave due to the presence of the large, subequal antapical horns. Paracingulum is well developed and is devoid of ornamentation on the paraplate surfaces, although high crests, surmounted by spines, are developed on, or close to, the anterior and posterior parasutures. The autophragm varies in thickness. Numerous short, solid, distally-pointed, thorn-shaped processes arise from the parasutures bordering the sagittal band, surmounting parasutural crests in the dorsal, ventral and antapical areas of the hypocyst, on the paracingular parasutures and on the epicyst. The processes at and close to the distal part of the antapical horns are frequently significantly longer than the spines elsewhere on the cyst. Spines may also be scattered in nontabular positions on the lateral parts of the hypocyst.
Dimensions (µm, n=35): Min. (Mean) Max.
Length of cyst body (excl. processes): 54 (67) 82
Width of cyst body (excl. processes): 30 (46) 65
Height of paracingulum: 7 (8) 12
Length of processes: 1 (3) 15
The measured specimens are all from a sidewall core sample in Jabiru-10 well at 1790.00m.
Ceomments. Nannoceratopsis spinosus is the only species of this genus which is proximochorate. The small, relativerly densely packed processes around the sagittal band and the prominent paracingulum, distinguish this taxon. The majority of the processes are parasutural and are typically centred around the sagittal band on the hypocyst, on or close to the paracingular parasutures and on the epicyst. Because of the extremely small size of the epicyst, resolution of the precise location of the epicystal spines is difficult. The processes at the distal tips of the antapical horns are frequently up to 15 µm, which is three times as long as the remaining spines. The majority of the processes are normally 2-4 µm long. The parasutural crests developed on the hypocyst adjacent to the sagittal band are surmounted by processes. The processes surrounding the anterior paracingular parasuture in the epicyst have a radiating pattern and often appear to form a corona. The nontabular processes on the hypocyst vary in density but are normally sparse. The surfaces of the cingular paraplates may be devoid of processes but are commonly microgranulate, scabrate or smooth. The paracingulum is consistently prominent, borad and slopes antapically from dorsal to ventral in lateral view.
Comparison. Nannoceratopsis spinosus differs from all other species of the genus in having parasutural and nontabular processes.
Derivation of name. From the Latin spinosus, meaning thorny.
Holotype and type locality. Fig. 7I, CPC 35156, Jabiru-10 well, sidewall core sample at 1790.00m.
Stratigraphical distribution. See Appendix 1.
Holotype: Riding and Helby, 2001a, fig.7I.
Age: early Toarcian.
Original description (Riding & Helby, 2001a):
Description. An acavate, relatively elongate species of Nannoceratopsis, intermediate in size and having two prominent, distally tapering, antapical horns of essentially similar size. The horns are distally pointed or rounded. The antapex is consistently markedly concave due to the presence of the large, subequal antapical horns. Paracingulum is well developed and is devoid of ornamentation on the paraplate surfaces, although high crests, surmounted by spines, are developed on, or close to, the anterior and posterior parasutures. The autophragm varies in thickness. Numerous short, solid, distally-pointed, thorn-shaped processes arise from the parasutures bordering the sagittal band, surmounting parasutural crests in the dorsal, ventral and antapical areas of the hypocyst, on the paracingular parasutures and on the epicyst. The processes at and close to the distal part of the antapical horns are frequently significantly longer than the spines elsewhere on the cyst. Spines may also be scattered in nontabular positions on the lateral parts of the hypocyst.
Dimensions (µm, n=35): Min. (Mean) Max.
Length of cyst body (excl. processes): 54 (67) 82
Width of cyst body (excl. processes): 30 (46) 65
Height of paracingulum: 7 (8) 12
Length of processes: 1 (3) 15
The measured specimens are all from a sidewall core sample in Jabiru-10 well at 1790.00m.
Ceomments. Nannoceratopsis spinosus is the only species of this genus which is proximochorate. The small, relativerly densely packed processes around the sagittal band and the prominent paracingulum, distinguish this taxon. The majority of the processes are parasutural and are typically centred around the sagittal band on the hypocyst, on or close to the paracingular parasutures and on the epicyst. Because of the extremely small size of the epicyst, resolution of the precise location of the epicystal spines is difficult. The processes at the distal tips of the antapical horns are frequently up to 15 µm, which is three times as long as the remaining spines. The majority of the processes are normally 2-4 µm long. The parasutural crests developed on the hypocyst adjacent to the sagittal band are surmounted by processes. The processes surrounding the anterior paracingular parasuture in the epicyst have a radiating pattern and often appear to form a corona. The nontabular processes on the hypocyst vary in density but are normally sparse. The surfaces of the cingular paraplates may be devoid of processes but are commonly microgranulate, scabrate or smooth. The paracingulum is consistently prominent, borad and slopes antapically from dorsal to ventral in lateral view.
Comparison. Nannoceratopsis spinosus differs from all other species of the genus in having parasutural and nontabular processes.
Derivation of name. From the Latin spinosus, meaning thorny.
Holotype and type locality. Fig. 7I, CPC 35156, Jabiru-10 well, sidewall core sample at 1790.00m.
Stratigraphical distribution. See Appendix 1.