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Frigatadinium frigatense
Frigatadinium frigatense Riding, 2004, p.238–239,241–242, figs.2A–B,3A–I.
Holotype: Riding, 2004, figs.3G–H.
Age: early Oxfordian–mid Berriasian.
Original description (Riding, 2004):
Description. An intermediate to large species of Frigatadinium with a short, foliate apical horn that may be formed of autophragm and/or coalescing/anastomosing solid, slender elements of ornamentation. It is dorsoventrally flattened and is elongate subhexagonal, subpentangular or biconical/subellipsoidal in dorsoventral view. The autophragm is robust and smooth to microscabrate; it is approximately I μm to I .5 μm in thickness. The parasutures indicate a sexiform gonyaulacalean paratabulation pattern with dextral torsion. The antapical (l "'') paraplate is relatively small. The paratabulation is marked by characteristic lineations of densely and evenly inserted parasutural elements which are trabeculate. However, some epicystal elements are not connected by trabeculae and these short spines/denticles are distally capitate. The parasutural elements are slender, solid, smooth and approximately 4 μm-5 μm in height. Some of the longer elements on the hypocyst bifurcate distally. They are typically longest on the hypocyst, becoming markedly more prominentin an antapical direction. The paracingulum is prominent and is indicated by lineations of trabeculate elements. The parasutural ornamentation is most prominent in the lateral and
dorsal areas, the ventral parasutures are markedly lower or are entirely suppressed. The I"' and 2 "' paraplates and the 6'" I parasulcal parasuture may be delineated, but the other paraplates and parasutures are typically missing or their presence may be indicated by discontinous, low relief ornamentation (Fig. 2). The cyst is divided into two equal hemispheres by the paracingulum, which normally is around 5 μm longitudinally and distinctly laevorotatory. The
ends of the paracingulum are displaced ventrally by up to twice the longitudinal height of the paracingulum. The parasulcus is relatively wide, longitudinal, and is not subdivided.
Dimensions. These are all in micrometres (μm); 20
specimens were measured. The figures given are the minimum, (mean) and maximum respectively. Overall length of cyst (incl. horn): 80 (98) l I 8 Overall width of cyst (incl. ornament): 58 (80) 95 Length of apical horn: 7 (IO) I3
Length of epicyst (incl. horn): 3 I ( 42) 60 Length ofhypocyst (incl. ornament): 40 (53) 69 Length of spines/denticles: 2 (5) I I The measured specimens are from a sidewall core from the Frigate-I well at I233.00m, ditch cuttings from the Hadrian-I well between 3295.00m and 3300.00m and outcrop material of the Tithonian Lelinta Formation (Fageo Group) fromMisool, eastern Indonesia (Hasibuan, 1990).
Comments. Frigatadinium frigatense is a highly distinctive species due to the characteristic, densely inserted parasutural trabeculate elements, wide parasulcus and the marked suppression of the ventral parasutures. It is a form in which recognition would be possible based upon a relatively small fragment of the hypocyst. The parasutural ornament of trabeculate short elements are somewhat variable, largely due to differences in length of these features, which would be spines/denticles if they were not connected distally, and also the possible presence
of distal furcations (Fig. 3). Some of the longer elements on the hypocyst bifurcate distally and this branching imparts a lacelike appearance. Occasionally, isolated or very small groups of nontabular short spines/denticles may be present; these are most common on the epicyst. The length of the parasutural ornamentation is higher on the
hypocyst and increases markedly towards the antapex. This phenomenon of antapically increasing process size is common in dinoflagellate cysts, e.g. Rotosphaeropsis thula (Davey 1982) Riding & Davey 1989. The ornamentational elements are dense and evenly inserted; typically the distance between them varies from 1 μm to 3.5 μm, but is normally 2 μm (Fig. 2). The antapical ( 1 "") paraplate is relatively small, and therefore Frigatadinium frigatense may be closely related to Cribroperidinium corrugatum Riding & Helby 2001. The latter species, from the mid to late Kimmeridgian (Dingodinium swanense Interval Zone) of Australia, also has an extremely small antapical
paraplate (Riding & Helby, 2001 ). The apical horn of Frigatadinium frigatense is variable in both size and form. Specimens with entire horns (i.e. extensions of the autophragm) are distally foliate (e.g. Fig. 3C). However, the horns of many individuals are formed from slender, solid, coalescing fibres or thin processes (e.g. Figs. 3D, 3I). The apical horns of these forms therefore resemble those of the Mid-Late Jurassic species Trichodinium scarburghense Sarjeant 1964) Williams et al. 1993 (see Drugg, 1978, pl. 4, figs 2, 3). Some forms comparable to Frigatadinium
frigatense are known which have numerous, dense, extremely thin fibres surmounting the parasutures (R. Helby, unpublished information). The density of these fibres is variable and these forms appear to intergrade with Frigatadinium frigatense sensu stricto.
Comparison. Frigatadinium is most similar in overall morphology and paratabulation formula to Cribroperidinium. Because this new genus is monotypic, Frigatadinium frigatense is here largely compared to similar species of Cribroperidinium. Species of Cribroperidinium consistently developed paratabulation and most of these have entire, distally smooth parasutural crests. However, the most similar species of Cribroperidinium to Frigatadinium frigatense is Cribroperidinium boreas (Davey 1984) Helenes 1984. Cribroperidinium boreas is from the late Barremian of eastern England and has prominent, fenestrate parasutural crests (Davey, 1974, pl. 4, figs 1-4 ). The parasutural ornamentation of these two species is somewhat similar, but the dorsal and lateral ornamentational elements of Frigatadiniumfrigatense are generally higher and are formed of distinct individual elements, which are joined distally. The parasutural crests of Cribroperidinium boreas are more entire and therefore genuinely fenestrate. Furthermore,
Frigatadiniumfrigatense is distinctly subangular, whereas Cribroperidinium boreas is ovoidal. Also Cribroperidinium boreas has a strongly ornamented autophragm and is significantly smaller than Frigatadinium frigatense. Similarly, Cribroperidinium? perforans (Cookson & Eisenack 1958) Morgan 1980 has prominent parasutural crests which are perforate. However, the fenestrae are small, subcircular and irregularly inserted (Cookson & Eisenack, 1958, figs 8, 9). Furthermore, the parasutural ornamentation on Cribroperidinium? perforans is concentrated apically, equatorially and antapically; a midlateral fragment of Cribroperidinium? perforans would typically have low parasutural ornamentation.The Kimmeridgian species Cribroperidinium complexum Bailey I 993 has parasutural crests that
may have proximal vacuoles. These perforate crests of Cribroperidinium complexum are irregularly developed, but most often present around the antapex (Bailey, I 993, pl. I). Cribroperidinium erymnoseptum Bailey 1993 also may have parasutural trabeculate spines. However, this form differs from Frigatadinium frigatense in that the parasutural ornament is highly variable and the low-relief ornamentation frequently comprises individual elements (Bailey, I993,pl.2). Another Late Jurassic species, Cribroperidinium swithini Williams et al. I 998, has perforate parasutural crests. However, this species has a prominently reticulate autophragm in addition to having irregularly perforate
parasutural crests (Brenner, I 988, pl. 3, figs 2, 5). The Late Cretaceous species Cribroperidinium graemei Williams et al. I 998 also has irregularly perforate parasutural crests which bear a superficial resemblance to the parasutural
ornamentation of Frigatadinium frigatense. However, Cribroperidinium graemei lacks evenly inserted trabeculate parasutural elements (Slimani, 1994,pl. I4,figs5-ll). Cribroperidinium wilsonii (Yun, I 98 I) Poulsen 1996 is characterised by a dense cover of parasutural and intratabular spines, however these are nottrabeculate (Yun, 1981, pl. 1, figs 2, 3, 6, 7). The Early Cretaceous type species, Cribroperidinium sepimentum Neale & Sarjeant 1962,
has wide, perforate parasutural crests; parasutural denticles are absent and this species also has a prominent apical horn and microperforate autophragm. Frigatadinium frigatense lacks the prominent intratabular ridges/crests that represent growth bands and are typical of many Cretaceous and Palaeogene representatives of Cribroperidinium, but are not a diagnostic feature (Gocht, 1979; Helenes, 1984, p. 110, 112). Frigatadinium frigatense has a relatively small antapical (1 "") paraplate, similar to that of Cribroperidinium corrugatum Riding & Helby, 200I, but the latter species has an extremely thick, corrugate autophragm and prominent parasutural crests,
which are irregularly perforate (Riding & Helby, 200I). Scriniodinium heikei Pross! 1990, from the Albian of north-west Germany, has perforate parasutural crests which strongly resemble the trabeculate parasutures of Frigatadinium frigatense (Pross!, 1990, pl. I2, figs I, 2, 4, 5, 9). However, Scriniodinium heikei is cavate, having a relatively small endocyst, and does not exhibit dextral torsion. The specimen of Rhynchodiniopsis serrata (Cookson & Eisenack I958) Jan du Chene et al. 1985 indicates that this species has partially suppressed parasutures in the midventral area immediately around the parasulcus (Jan du Chene et al., I986, pl. 99, fig. I). However Rhynchodiniopsis
serrata does not exhibit dextral torsion and the parasutural ornament is not trabeculate. Derivation of name. From the Frigate-I well. Holotype and type locality. Figs 3G and 3H, specimen CPC 3667 I, from a sidewall core sample
in the Frigate Shale Unit (Flamingo Group) of the Frigate-I well at I233.00m. Stratigraphical and Geographical Distribution. Frigatadinium frigatense ranges from the early Oxfordian to the mid Berriasian in Australia, Papua
New Guinea, New Zealand and Misool, eastern Indonesia. In Australia, it has been recorded from the Carnarvon Basin and the Timor Sea region. The Australasian zonal range of the species is from the lower Wanaea spectabilis Interval Zone (Subzone 6ciii) to the upper Cassiculosphaeridia delicata Interval Zone (Subzone 4bi). The zones
are ofHelby"et al. (I987) and the subzones that subdivide these were illustrated, but not defined, by Foster (200I, fig. 2). Frigatadinium frigatense is most consistently present from the mid-late Kimmeridgian to the mid Tithonian; this interval comprises the mid Dingodinium swanense Interval Zone (Subzone 6aii) to the upper Dingodiniumjurassicum Oppel Zone (Subzone 5aii). The species has previously been reported as gen. et sp. indet. H from the Tithonian Kinohaku and Puti Siltstones of Kawhia, New Zealand by Helby et al. (1988, figs I6L, I9L).
Holotype: Riding, 2004, figs.3G–H.
Age: early Oxfordian–mid Berriasian.
Original description (Riding, 2004):
Description. An intermediate to large species of Frigatadinium with a short, foliate apical horn that may be formed of autophragm and/or coalescing/anastomosing solid, slender elements of ornamentation. It is dorsoventrally flattened and is elongate subhexagonal, subpentangular or biconical/subellipsoidal in dorsoventral view. The autophragm is robust and smooth to microscabrate; it is approximately I μm to I .5 μm in thickness. The parasutures indicate a sexiform gonyaulacalean paratabulation pattern with dextral torsion. The antapical (l "'') paraplate is relatively small. The paratabulation is marked by characteristic lineations of densely and evenly inserted parasutural elements which are trabeculate. However, some epicystal elements are not connected by trabeculae and these short spines/denticles are distally capitate. The parasutural elements are slender, solid, smooth and approximately 4 μm-5 μm in height. Some of the longer elements on the hypocyst bifurcate distally. They are typically longest on the hypocyst, becoming markedly more prominentin an antapical direction. The paracingulum is prominent and is indicated by lineations of trabeculate elements. The parasutural ornamentation is most prominent in the lateral and
dorsal areas, the ventral parasutures are markedly lower or are entirely suppressed. The I"' and 2 "' paraplates and the 6'" I parasulcal parasuture may be delineated, but the other paraplates and parasutures are typically missing or their presence may be indicated by discontinous, low relief ornamentation (Fig. 2). The cyst is divided into two equal hemispheres by the paracingulum, which normally is around 5 μm longitudinally and distinctly laevorotatory. The
ends of the paracingulum are displaced ventrally by up to twice the longitudinal height of the paracingulum. The parasulcus is relatively wide, longitudinal, and is not subdivided.
Dimensions. These are all in micrometres (μm); 20
specimens were measured. The figures given are the minimum, (mean) and maximum respectively. Overall length of cyst (incl. horn): 80 (98) l I 8 Overall width of cyst (incl. ornament): 58 (80) 95 Length of apical horn: 7 (IO) I3
Length of epicyst (incl. horn): 3 I ( 42) 60 Length ofhypocyst (incl. ornament): 40 (53) 69 Length of spines/denticles: 2 (5) I I The measured specimens are from a sidewall core from the Frigate-I well at I233.00m, ditch cuttings from the Hadrian-I well between 3295.00m and 3300.00m and outcrop material of the Tithonian Lelinta Formation (Fageo Group) fromMisool, eastern Indonesia (Hasibuan, 1990).
Comments. Frigatadinium frigatense is a highly distinctive species due to the characteristic, densely inserted parasutural trabeculate elements, wide parasulcus and the marked suppression of the ventral parasutures. It is a form in which recognition would be possible based upon a relatively small fragment of the hypocyst. The parasutural ornament of trabeculate short elements are somewhat variable, largely due to differences in length of these features, which would be spines/denticles if they were not connected distally, and also the possible presence
of distal furcations (Fig. 3). Some of the longer elements on the hypocyst bifurcate distally and this branching imparts a lacelike appearance. Occasionally, isolated or very small groups of nontabular short spines/denticles may be present; these are most common on the epicyst. The length of the parasutural ornamentation is higher on the
hypocyst and increases markedly towards the antapex. This phenomenon of antapically increasing process size is common in dinoflagellate cysts, e.g. Rotosphaeropsis thula (Davey 1982) Riding & Davey 1989. The ornamentational elements are dense and evenly inserted; typically the distance between them varies from 1 μm to 3.5 μm, but is normally 2 μm (Fig. 2). The antapical ( 1 "") paraplate is relatively small, and therefore Frigatadinium frigatense may be closely related to Cribroperidinium corrugatum Riding & Helby 2001. The latter species, from the mid to late Kimmeridgian (Dingodinium swanense Interval Zone) of Australia, also has an extremely small antapical
paraplate (Riding & Helby, 2001 ). The apical horn of Frigatadinium frigatense is variable in both size and form. Specimens with entire horns (i.e. extensions of the autophragm) are distally foliate (e.g. Fig. 3C). However, the horns of many individuals are formed from slender, solid, coalescing fibres or thin processes (e.g. Figs. 3D, 3I). The apical horns of these forms therefore resemble those of the Mid-Late Jurassic species Trichodinium scarburghense Sarjeant 1964) Williams et al. 1993 (see Drugg, 1978, pl. 4, figs 2, 3). Some forms comparable to Frigatadinium
frigatense are known which have numerous, dense, extremely thin fibres surmounting the parasutures (R. Helby, unpublished information). The density of these fibres is variable and these forms appear to intergrade with Frigatadinium frigatense sensu stricto.
Comparison. Frigatadinium is most similar in overall morphology and paratabulation formula to Cribroperidinium. Because this new genus is monotypic, Frigatadinium frigatense is here largely compared to similar species of Cribroperidinium. Species of Cribroperidinium consistently developed paratabulation and most of these have entire, distally smooth parasutural crests. However, the most similar species of Cribroperidinium to Frigatadinium frigatense is Cribroperidinium boreas (Davey 1984) Helenes 1984. Cribroperidinium boreas is from the late Barremian of eastern England and has prominent, fenestrate parasutural crests (Davey, 1974, pl. 4, figs 1-4 ). The parasutural ornamentation of these two species is somewhat similar, but the dorsal and lateral ornamentational elements of Frigatadiniumfrigatense are generally higher and are formed of distinct individual elements, which are joined distally. The parasutural crests of Cribroperidinium boreas are more entire and therefore genuinely fenestrate. Furthermore,
Frigatadiniumfrigatense is distinctly subangular, whereas Cribroperidinium boreas is ovoidal. Also Cribroperidinium boreas has a strongly ornamented autophragm and is significantly smaller than Frigatadinium frigatense. Similarly, Cribroperidinium? perforans (Cookson & Eisenack 1958) Morgan 1980 has prominent parasutural crests which are perforate. However, the fenestrae are small, subcircular and irregularly inserted (Cookson & Eisenack, 1958, figs 8, 9). Furthermore, the parasutural ornamentation on Cribroperidinium? perforans is concentrated apically, equatorially and antapically; a midlateral fragment of Cribroperidinium? perforans would typically have low parasutural ornamentation.The Kimmeridgian species Cribroperidinium complexum Bailey I 993 has parasutural crests that
may have proximal vacuoles. These perforate crests of Cribroperidinium complexum are irregularly developed, but most often present around the antapex (Bailey, I 993, pl. I). Cribroperidinium erymnoseptum Bailey 1993 also may have parasutural trabeculate spines. However, this form differs from Frigatadinium frigatense in that the parasutural ornament is highly variable and the low-relief ornamentation frequently comprises individual elements (Bailey, I993,pl.2). Another Late Jurassic species, Cribroperidinium swithini Williams et al. I 998, has perforate parasutural crests. However, this species has a prominently reticulate autophragm in addition to having irregularly perforate
parasutural crests (Brenner, I 988, pl. 3, figs 2, 5). The Late Cretaceous species Cribroperidinium graemei Williams et al. I 998 also has irregularly perforate parasutural crests which bear a superficial resemblance to the parasutural
ornamentation of Frigatadinium frigatense. However, Cribroperidinium graemei lacks evenly inserted trabeculate parasutural elements (Slimani, 1994,pl. I4,figs5-ll). Cribroperidinium wilsonii (Yun, I 98 I) Poulsen 1996 is characterised by a dense cover of parasutural and intratabular spines, however these are nottrabeculate (Yun, 1981, pl. 1, figs 2, 3, 6, 7). The Early Cretaceous type species, Cribroperidinium sepimentum Neale & Sarjeant 1962,
has wide, perforate parasutural crests; parasutural denticles are absent and this species also has a prominent apical horn and microperforate autophragm. Frigatadinium frigatense lacks the prominent intratabular ridges/crests that represent growth bands and are typical of many Cretaceous and Palaeogene representatives of Cribroperidinium, but are not a diagnostic feature (Gocht, 1979; Helenes, 1984, p. 110, 112). Frigatadinium frigatense has a relatively small antapical (1 "") paraplate, similar to that of Cribroperidinium corrugatum Riding & Helby, 200I, but the latter species has an extremely thick, corrugate autophragm and prominent parasutural crests,
which are irregularly perforate (Riding & Helby, 200I). Scriniodinium heikei Pross! 1990, from the Albian of north-west Germany, has perforate parasutural crests which strongly resemble the trabeculate parasutures of Frigatadinium frigatense (Pross!, 1990, pl. I2, figs I, 2, 4, 5, 9). However, Scriniodinium heikei is cavate, having a relatively small endocyst, and does not exhibit dextral torsion. The specimen of Rhynchodiniopsis serrata (Cookson & Eisenack I958) Jan du Chene et al. 1985 indicates that this species has partially suppressed parasutures in the midventral area immediately around the parasulcus (Jan du Chene et al., I986, pl. 99, fig. I). However Rhynchodiniopsis
serrata does not exhibit dextral torsion and the parasutural ornament is not trabeculate. Derivation of name. From the Frigate-I well. Holotype and type locality. Figs 3G and 3H, specimen CPC 3667 I, from a sidewall core sample
in the Frigate Shale Unit (Flamingo Group) of the Frigate-I well at I233.00m. Stratigraphical and Geographical Distribution. Frigatadinium frigatense ranges from the early Oxfordian to the mid Berriasian in Australia, Papua
New Guinea, New Zealand and Misool, eastern Indonesia. In Australia, it has been recorded from the Carnarvon Basin and the Timor Sea region. The Australasian zonal range of the species is from the lower Wanaea spectabilis Interval Zone (Subzone 6ciii) to the upper Cassiculosphaeridia delicata Interval Zone (Subzone 4bi). The zones
are ofHelby"et al. (I987) and the subzones that subdivide these were illustrated, but not defined, by Foster (200I, fig. 2). Frigatadinium frigatense is most consistently present from the mid-late Kimmeridgian to the mid Tithonian; this interval comprises the mid Dingodinium swanense Interval Zone (Subzone 6aii) to the upper Dingodiniumjurassicum Oppel Zone (Subzone 5aii). The species has previously been reported as gen. et sp. indet. H from the Tithonian Kinohaku and Puti Siltstones of Kawhia, New Zealand by Helby et al. (1988, figs I6L, I9L).