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Gonyaulacysta ceratophora
Gonyaulacysta ceratophora (Cookson and Eisenack, 1960b, p.249, pl.37, fig.7) Riding, 2005b, p.14. Emendation: Riding, 2005a, p.14,16,18, as Gonyaulacysta ceratophora.
Originally Scriniodinium, subsequently Scriniodinium?, thirdly (and now) Gonyaulacysta.
Taxonomic junior synonym: Psaligonyaulax australica, according to Jan du Chêne et al. (1986a, p.266) — however, Psaligonyaulax australica is now considered a taxonomic junior synonym of Psaligonyaulax (as Gonyaulacysta) dualis.
Holotype: Cookson and Eisenack, 1960b, pl.37, fig.7; Jan du Chêne et al., 1986a, pl.112, fig.1; Helby et al., 1987, fig.18C: Riding, 2005a, text-figs.2A–B.
Age: Oxfordian–early Kimmeridgian.
Original description: Cookson and Eisenack, 1960, p. 249.
Description: Shell flat, consisting of a larger triangular epitheca and a smaller rounded hypotheca which are separated by an apparently broad girdle with thin borders. Shell-membrane thin, either smooth or, as in the type, finely granular, prolonged into a well-developed apical horn having a truncate apex with a small median projection. The capsule has a small apical prominence and almost fills the shell. A large pylome is developed in the vicinity of the girdle.
Dimensions: Holotype: 125 µm long, 94 µm broad, capsule 97 x 96 µm, horn 24 µm. Another specimen: 110 µm long, 71 µm broad, capsule 70 x 67 µm, horn 33 µm.
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Emended diagnosis: Riding, 2005b, p.14:
Diagnosis. A partially tabulate to non-tabulate species of Gonyaulacysta. The midventral and middorsal areas normally lack any indications of tabulation. Where developed, low sutural ridges or crests are generally restricted to the antapical-lateral and apical areas. A poorly developed hypopericoel is usually developed.
Emended description. A large, elongate, dorsoventrally flattened species of Gonyaulacysta. It is normally epicavate to bicavate, with a prominent, long, narrow, distally truncate, apical horn formed by the periphragm. The epipericoel is consistently prominent and is emphasized by the large apical horn. The hypopericoel, where developed, is narrow. Some specimens have narrow pericoels partially developed in the equatorial regions, and therefore approach a circumcavate condition. The pericyst, not including the apical horn, is elongate subellipsoidal to rounded subpentagonal and is markedly truncate antapically. The periphragm is relatively thin (< 1 µm) and is smooth, microscabrate, scabrate, granulate, papillate or verrucate. It is susceptible to mechanical folding and may also occasionally be irregularly microreticulate. The endocyst mirrors the pericystal outline, i.e. it is elongate ellipsoidal, and may have a distally rounded apical protuberance. The endophragm is smooth to microscabrate and is relatively thick (approximately 1 µm). The cornucavate epicyst is relatively large, and typically represents between 65% and 70% of the overall cyst length. A sexiform gonyaulacacean tabulation with neutral torsion may be partially indicated by low sutural ridges and/or crests. The cingulum is normally fully indicated; however, the majority of the remaining tabulation is reduced or suppressed. In specimens where sutures are partially developed, the posterior intercalary plate and the antapical plate are normally fully indicated. Elsewhere, largely incomplete sutures are generally present only on the lateral areas of the hypocyst and around the apical horn. The tabulation, where developed, is manifested as low, smooth ridges and/or smooth to sparsely and irregularly denticulate crests. Occasionally, the sutural crests may be distally irregular or undulose. Denticles are most common on crests surrounding the antapical (1'''') plate. Occasional isolated, sinuous, solid, distally simple, capitate or furcate sutural spines up to approximately 15 µm long may also be present on hypocystal sutures. These are most prevalent in the antapical-lateral areas, but they are rarely present on the postcingular sutures and around the cingulum. Prominent gonal spines are regularly developed around the antapical (1'''') plate. Midventral and middorsal areas are typically devoid of tabulation. The archeopyle is monoplacoid precingular, type P3'', with a free endoperculum. A perioperculum is apparently absent and the prominent endoperculum is frequently displaced into the endocyst. Both the periarcheopyle and the endoarcheopyle may occasionally be slightly enlarged posteriorly, at the 3''/3c–4c plate boundary. A subcircular opisthopyle may be present in the posterior sulcal (ps) plate.
Dimensions. Cookson and Eisenack (1960) measured two specimens, the holotype and an unfigured paratype. The pericyst of the holotype is 125 µm in length, 94 µm in width, with an apical horn length of 24 µm. The endocyst of the holotype is 96 µm x 97 µm. The pericyst of the unfigured paratype is 110 µm long, 71 µm wide, with an apical horn 33 µm in length; the endocyst is 67 µm x 70 µm.
These dimensions are comparable with the size of the specimens studied here (Table 1). These are all in micrometers (µm); 17 specimens were measured. The measured specimens in Table 1 are all from the Middle Oxfordian of the Arunta-1 and Buang-1 wells. Specifically, the material comprises sidewall core samples from the Lower Vulcan Formation (Patillo and Nichols, 1990) of the Arunta-1 well at 1805.00 m and the Frigate Formation (Whittam et al., 1996) of the Buang-1 well at 3518.50 m (Text-Figure 3; Appendix 1). Both these wells were drilled in the Timor Sea and both are within the Bonaparte Basin (Text-Figure 3). The type material is from the Broome Number 3 Borehole in the Canning Basin, over 700 km to the southwest (Text-Figure 3; Foster, 2001, textfig. 1).
Remarks. This species is significantly more variable than indicated by Cookson and Eisenack (1960), who illustrated only smooth, non-tabulate end members. The species may be partially tabulate; see for example the specimens illustrated by Jan du Chêne et al. (1986, pl. 112, figs 2, 3), Keating et al. (1992, text-figs 6i, 6j) and herein in Plate 1 and Text-Figure 1C, D. The species may also be strongly ornamented; Helby et al. (1988, text-fig. 9S) figured a densely granulate/verrucate specimen that they assigned to Scriniodinium sp. cf. S. ceratophorum from the Waikutakuta Siltstone (Upper Jurassic; Kimmeridgian) of Kawhia, southwest Auckland, North Island, New Zealand
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Originally Scriniodinium, subsequently Scriniodinium?, thirdly (and now) Gonyaulacysta.
Taxonomic junior synonym: Psaligonyaulax australica, according to Jan du Chêne et al. (1986a, p.266) — however, Psaligonyaulax australica is now considered a taxonomic junior synonym of Psaligonyaulax (as Gonyaulacysta) dualis.
Holotype: Cookson and Eisenack, 1960b, pl.37, fig.7; Jan du Chêne et al., 1986a, pl.112, fig.1; Helby et al., 1987, fig.18C: Riding, 2005a, text-figs.2A–B.
Age: Oxfordian–early Kimmeridgian.
Original description: Cookson and Eisenack, 1960, p. 249.
Description: Shell flat, consisting of a larger triangular epitheca and a smaller rounded hypotheca which are separated by an apparently broad girdle with thin borders. Shell-membrane thin, either smooth or, as in the type, finely granular, prolonged into a well-developed apical horn having a truncate apex with a small median projection. The capsule has a small apical prominence and almost fills the shell. A large pylome is developed in the vicinity of the girdle.
Dimensions: Holotype: 125 µm long, 94 µm broad, capsule 97 x 96 µm, horn 24 µm. Another specimen: 110 µm long, 71 µm broad, capsule 70 x 67 µm, horn 33 µm.
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Emended diagnosis: Riding, 2005b, p.14:
Diagnosis. A partially tabulate to non-tabulate species of Gonyaulacysta. The midventral and middorsal areas normally lack any indications of tabulation. Where developed, low sutural ridges or crests are generally restricted to the antapical-lateral and apical areas. A poorly developed hypopericoel is usually developed.
Emended description. A large, elongate, dorsoventrally flattened species of Gonyaulacysta. It is normally epicavate to bicavate, with a prominent, long, narrow, distally truncate, apical horn formed by the periphragm. The epipericoel is consistently prominent and is emphasized by the large apical horn. The hypopericoel, where developed, is narrow. Some specimens have narrow pericoels partially developed in the equatorial regions, and therefore approach a circumcavate condition. The pericyst, not including the apical horn, is elongate subellipsoidal to rounded subpentagonal and is markedly truncate antapically. The periphragm is relatively thin (< 1 µm) and is smooth, microscabrate, scabrate, granulate, papillate or verrucate. It is susceptible to mechanical folding and may also occasionally be irregularly microreticulate. The endocyst mirrors the pericystal outline, i.e. it is elongate ellipsoidal, and may have a distally rounded apical protuberance. The endophragm is smooth to microscabrate and is relatively thick (approximately 1 µm). The cornucavate epicyst is relatively large, and typically represents between 65% and 70% of the overall cyst length. A sexiform gonyaulacacean tabulation with neutral torsion may be partially indicated by low sutural ridges and/or crests. The cingulum is normally fully indicated; however, the majority of the remaining tabulation is reduced or suppressed. In specimens where sutures are partially developed, the posterior intercalary plate and the antapical plate are normally fully indicated. Elsewhere, largely incomplete sutures are generally present only on the lateral areas of the hypocyst and around the apical horn. The tabulation, where developed, is manifested as low, smooth ridges and/or smooth to sparsely and irregularly denticulate crests. Occasionally, the sutural crests may be distally irregular or undulose. Denticles are most common on crests surrounding the antapical (1'''') plate. Occasional isolated, sinuous, solid, distally simple, capitate or furcate sutural spines up to approximately 15 µm long may also be present on hypocystal sutures. These are most prevalent in the antapical-lateral areas, but they are rarely present on the postcingular sutures and around the cingulum. Prominent gonal spines are regularly developed around the antapical (1'''') plate. Midventral and middorsal areas are typically devoid of tabulation. The archeopyle is monoplacoid precingular, type P3'', with a free endoperculum. A perioperculum is apparently absent and the prominent endoperculum is frequently displaced into the endocyst. Both the periarcheopyle and the endoarcheopyle may occasionally be slightly enlarged posteriorly, at the 3''/3c–4c plate boundary. A subcircular opisthopyle may be present in the posterior sulcal (ps) plate.
Dimensions. Cookson and Eisenack (1960) measured two specimens, the holotype and an unfigured paratype. The pericyst of the holotype is 125 µm in length, 94 µm in width, with an apical horn length of 24 µm. The endocyst of the holotype is 96 µm x 97 µm. The pericyst of the unfigured paratype is 110 µm long, 71 µm wide, with an apical horn 33 µm in length; the endocyst is 67 µm x 70 µm.
These dimensions are comparable with the size of the specimens studied here (Table 1). These are all in micrometers (µm); 17 specimens were measured. The measured specimens in Table 1 are all from the Middle Oxfordian of the Arunta-1 and Buang-1 wells. Specifically, the material comprises sidewall core samples from the Lower Vulcan Formation (Patillo and Nichols, 1990) of the Arunta-1 well at 1805.00 m and the Frigate Formation (Whittam et al., 1996) of the Buang-1 well at 3518.50 m (Text-Figure 3; Appendix 1). Both these wells were drilled in the Timor Sea and both are within the Bonaparte Basin (Text-Figure 3). The type material is from the Broome Number 3 Borehole in the Canning Basin, over 700 km to the southwest (Text-Figure 3; Foster, 2001, textfig. 1).
Remarks. This species is significantly more variable than indicated by Cookson and Eisenack (1960), who illustrated only smooth, non-tabulate end members. The species may be partially tabulate; see for example the specimens illustrated by Jan du Chêne et al. (1986, pl. 112, figs 2, 3), Keating et al. (1992, text-figs 6i, 6j) and herein in Plate 1 and Text-Figure 1C, D. The species may also be strongly ornamented; Helby et al. (1988, text-fig. 9S) figured a densely granulate/verrucate specimen that they assigned to Scriniodinium sp. cf. S. ceratophorum from the Waikutakuta Siltstone (Upper Jurassic; Kimmeridgian) of Kawhia, southwest Auckland, North Island, New Zealand
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