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Gonyaulacysta dualis
From Fensome et al., 2019:
Gonyaulacacysta dualis (Brideaux and Fisher, 1976, p.18–20, pl.1, figs.4–6,8–12; pl.2, figs.1–2) Stover and Evitt, 1978, p.158. Holotype: Brideaux and Fisher, 1976, pl.1, figs.4–5; Jan du Chêne et al., 1986a, pl.37, figs.11–12. Originally Psaligonyaulax, subsequently (and now) Gonyaulacysta. Taxonomic senior synonym: Gonyaulax (as Gonyaulacysta) jurassica, according to Sarjeant (1982b, p.29) — however, Jan du Chêne et al. (1986a, p.131) retained Gonyaulacysta dualis. Taxonomic junior synonym: Psaligonyaulax australica, according to Brenner (1988, p.54). Age: late Oxfordian–late Kimmeridgian.
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Locus typicus: Elf Horton River, N Canada
Stratum typicum: Late Oxfordian-Late Kimmeridgian
Original description: Brideaux and Fisher, 1976, p. 18: Psaligonyaulax dualis Diagnosis: Periblast elongate, typically twice as long as broad, with sligthly tapering apical horn; endoblast rhomboid with a short apical prominence and rounded antapex. Antapical breach typically present in the periblast, rarely closed by a moderately bulging antapical prominence. Periblast and endoblast in close contact only at latitude of cingulum, resulting in formation of distinct apical and antapical pericoels. Surface of periphragm and endophragm smooth or, rarely, scabrate. Archaeopyle in each layer formed by loss of third reflected precingular plate; opercula separate and detached, elongate. Periblast forms sutural crests which outline a reflected tabulation of 1pr, 4', 6'', 6c, 5'''-?6''', 1p, 1''''; crests variable, entire to denticulate, rarely spiny. Cingulum displaced up to two cingular widths, distinct; reflected sulcal tabulation absent but sulcal region distinct.
Dimensions: Holotype: Periblast length 125 µm, width 95µm; endoblast length 74 µm. Range: Periblast length 93-135 µm; apical horn 20-33 µm; endoblast length 63-100 µm; endoblast horn 3-9 µm; periblast width 40-83µm. 25 specimens measured.
For an elaborate description see Brideaux and Fisher, 1976, p. 18-19
Affinities:
Brideaux and Fisher, 1976, p. 19 : Psaligonyaulax dualis
P. dualis differs from previously published species of the genus in the following ways: from P. deflanfrei Sarjeant by its larger size, more prominent apical horn, rhombic endoblast and details of tabulation; from P. apatela (Cookson and Eisenack) Sarjeant in overal shape, greater overall length and length of apical horn, type of sutural crests, shape of the endophragm, and details of tabulation; and from P. simplicia (Cookson and Eisenack) Sarjeant in shape, form of sutures, details of tabulation, and other features. P. dualis bears a superficial similarity to Gonyaulacacysta jurassica (Deflandre) Norris and Sarjeant, but differs in at least four features. The size of the periblast and endoblast is generally larger, the smaller specimens of P. dualis overlapping only with the largest speicmens of G. jurassica; P. dualis has well-developed apical and antapical pericoels; specimens with a pronounced apical pericoel assigned to G. jurassica by Sarjeant differ in that the pericoel is formed by broadening of the apical horn at its base. P. dualis has a consistently well-developed antapical breach in the periblast, and more rarely, an antapical bulge. Finally, the endoblast of P. dualis exhibits a consistently rhombic outline.
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Emended description Riding et al., 2022:
Emended diagnosis: A large, elongate, bicavate species of Gonyaulacysta with a prominent apical horn formed of periphragm and a marked apical protuberance on the endocyst. Most of the sutural features are smooth ridges, but sporadically denticulate sutural crests and ridges may be developed. The sulcus is L-type and longitudinal.
Emended description: A large, elongate species of Gonyaulacysta with a bicavate cyst. Some of the precingular and postcingular plate boundaries may exhibit suturocavation. The epipericoel and hypopericoel are both large. It has a long, slender, distally truncate apical horn composed of periphragm. The endocyst exhibits a prominent rounded apical protuberance which may attain 8 μm in height. The tabulation comprises sutural ridges or crests that are usually low and distally smooth. However, these sutural features may bear small, pointed denticles. Denticulate sutural crests/ridges typically occur around the cingulum, in the lateral regions and rarely surrounding the 1′′′′ plate. Additionally, the antapical plate may bear relatively prominent gonal spines up to 5 μm in length. The longitudinal L-type sulcus and an opisthopyle are usually evident; the latter is subcircular to ellipsoidal and varies greatly in size. The periphragm may be smooth to markedly scabrate; the thicker endophragm is consistently smooth. The periarchaeopyle is large and may extend above the top of the endocyst.
Holotype: Brideaux and Fisher (1976, pl. 1, 4–5). Geological Survey of Canada (GSC) type number 34154; GSC location number C-12532, slide P810-13B. Ditch cuttings sample from the Gilmore LakeMember of the Langton Bay Formation, (upper Oxfordian–middle Kimmeridgian) between 552 m and 549 m in the Elf Horton River G-02 well, District of Mackenzie (now Northwest Territories), Canada. Specimen curated in the National Collection of Type Invertebrate and Plant Fossils, GSC, Ottawa, Ontario, Canada. At the time of writing, the specimen is on longterm loan to GSC Calgary.
Comments: This species was established by Brideaux and Fisher (1976) as Psaligonyaulax dualis, and transferred to Gonyaulacysta by Stover and Evitt (1978, p. 158). Psaligonyaulax has an equatorial cingulum and does not exhibit an opisthopyle (Sarjeant, 1966, fig. 35). Sarjeant (1982, p. 29) considered Psaligonyaulax dualis to be a taxonomic junior synonym of Gonyaulacysta jurassica, but Jan du Chêne et al. (1986, p. 131) retained Gonyaulacysta dualis as a separate species. Gonyaulacysta dualis is emended herein to stress its large size, slender and elongate outline, bicavate cyst organisation, prominent apical horn, and largely distally smooth sutures. Also highly distinctive is the long, thin apical horn, which has the form of an elongate and distally truncated cone. This feature ismirrored by a prominent apical protuberance on the endocyst. Gonyaulacysta dualis is bicavate, with large polar pericoels. Sutural features are usually low, distally smooth ridges, but low, occasionally denticulate crests may be developed (Brideaux and Fisher, 1976, pl. 1, 9–11). Other features that may be present are gonal spines around the 1′′′′ plate, and a scabrate periphragm (Plate VIII). Sarjeant (1982, p. 31–32; pl. 5, 5, 6) established Gonyaulacysta jurassica subsp. jurassica var. longicornuta. The single specimen figured by Sarjeant (1982) is virtually identical in all respects to the holotype of Gonyaulacysta dualis. Hence it is clear that Gonyaulacysta jurassica subsp. jurassica var. longicornuta is a taxonomic junior synonymof Gonyaulacysta dualis. We consider that the specimen illustrated as Gonyaulacysta dualis by Burger (1996, pl. 6W) is a misidentification of Gonyaulacysta jurassica.
Comparison: The most similar species to Gonyaulacysta dualis is Gonyaulacysta longicornis (not to be confused with Gonyaulacysta jurassica subsp. jurassica var. longicornuta of Sarjeant, 1982). However Gonyaulacysta longicornis is epicavate and has highly denticulate sutural crests. Gonyaulacysta dualis is also morphologically close to Gonyaulacysta ceratophora and Gonyaulacysta jurassica. However, Gonyaulacysta ceratophora lacks full tabulation and Gonyaulacysta jurassica is characterised by sutural crests which are high and densely denticulate (Fig. 2).
Dimensions: Gonyaulacysta dualis is a large species; the dimensions of the material from Alaska studied herein based on 30 specimens are: length of pericyst, 93 (109) 122; length of apical horn, 20 (28) 38; length of epipericyst, 53 (66) 75; length of hypopericyst, 22 (36) 49; length of endocyst, 62 (73) 91; width at cingulum, 55 (70) 80 (Supplementary material Appendix 3, table 9). This compares well with measurements of the type material by Brideaux and Fisher (1976, p. 19): length of pericyst, 93–135; length of apical horn, 20–33; length of endocyst, 63–100; length of protuberance on the endocyst, 3–9; width at cingulum, 40–83.
Geographical and stratigraphical distribution: Gonyaulacysta dualis is largely confined to the Oxfordian and Kimmeridgian (Late Jurassic) of the high palaeolatitudes of North America. The stratigraphical extent of the original material from Arctic Canada is upper Oxfordian to middle Kimmeridgian (Brideaux and Fisher, 1976, p. 19–20, fig. 13). These authors stated that the species is sporadic in the upper Kimmeridgian. Riding and Lucas-Clark (2016, pl. 2, 2; pl. 16, 4–6) figured specimens of Gonyaulacysta dualis from the Oxfordian of southwestern Alaska. This species was also recorded from the upper Oxfordian to upper Kimmeridgian, and the Oxfordian to middle Kimmeridgian of the Sverdrup Basin, Arctic Canada by Tan and Hills (1978) and Davies (1983) respectively. It was also recorded by Sarjeant (1982) from the lower to middle Kimmeridgian of northern Canada. Brideaux and Fisher (1976, p. 19) stated that some specimens of Gonyualacysta longicornis from Europe closely resemble Gonyaulacysta dualis. However, in our view, the specimens figured by Klement (1960, pl. 2, 6–8), Sarjeant (1962, pl.1, 3) and Gitmez (1970, pl. 5, 11) have prominent denticulate sutural crests and are epicavate, and hence do not belong to Gonyaulacysta dualis. Likewise, we believe that the specimens of Gonyaulacysta dualis figured by Brenner (1988, pl. 8, 2, 5), with their high, denticulate sutural crests, relatively short apical horns, and lack of apical protuberances on the endocyst, belong to Gonyaulacysta jurassica. Riding et al. (1999, pl. RP8, 5; pl. RP9, 2, 3, 6) figured specimens assigned to Gonyaulacysta dualis from the middle and upper Oxfordian of the Russian Platform. However, these specimens are epicavate, lack a well-developed apical protuberance on the endocyst, and the specimens on plate RP9 lack obvious tabulation in the equatorial area; hence they do not belong to Gonyaulacysta dualis. The only positive identification of Gonyaulacysta dualis from Europe is a specimen illustrated from the lowermost Kimmeridgian of Denmark by Poulsen (1996, pl. 4, 1).
Cookson and Eisenack (1982, p. 37–38) described Psaligonyaulax australica from the upper part of the Dingo Claystone of the Carnarvon Basin of Western Australia (Oxfordian to lower Kimmeridgian). Brenner (1988, p. 54) stated that Psaligonyaulax australica is a junior synonym of Gonyaulacysta dualis. The holotype of Psaligonyaulax australica is large, elongate, and has largely smooth sutural ridges, and so is somewhat similar in morphology to Gonyaulacysta dualis and has a similar stratigraphical range. However, the apical horn of Psaligonyaulax australica is smaller than is normal for Gonyaulacysta dualis, and the former has a semicircular hypocyst. Thus, we do not follow the synonymy proposed by Brenner (1988). Psaligonyaulax australica is herein transferred to Gonyaulacysta (see this section, above).
Gonyaulacacysta dualis (Brideaux and Fisher, 1976, p.18–20, pl.1, figs.4–6,8–12; pl.2, figs.1–2) Stover and Evitt, 1978, p.158. Holotype: Brideaux and Fisher, 1976, pl.1, figs.4–5; Jan du Chêne et al., 1986a, pl.37, figs.11–12. Originally Psaligonyaulax, subsequently (and now) Gonyaulacysta. Taxonomic senior synonym: Gonyaulax (as Gonyaulacysta) jurassica, according to Sarjeant (1982b, p.29) — however, Jan du Chêne et al. (1986a, p.131) retained Gonyaulacysta dualis. Taxonomic junior synonym: Psaligonyaulax australica, according to Brenner (1988, p.54). Age: late Oxfordian–late Kimmeridgian.
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Locus typicus: Elf Horton River, N Canada
Stratum typicum: Late Oxfordian-Late Kimmeridgian
Original description: Brideaux and Fisher, 1976, p. 18: Psaligonyaulax dualis Diagnosis: Periblast elongate, typically twice as long as broad, with sligthly tapering apical horn; endoblast rhomboid with a short apical prominence and rounded antapex. Antapical breach typically present in the periblast, rarely closed by a moderately bulging antapical prominence. Periblast and endoblast in close contact only at latitude of cingulum, resulting in formation of distinct apical and antapical pericoels. Surface of periphragm and endophragm smooth or, rarely, scabrate. Archaeopyle in each layer formed by loss of third reflected precingular plate; opercula separate and detached, elongate. Periblast forms sutural crests which outline a reflected tabulation of 1pr, 4', 6'', 6c, 5'''-?6''', 1p, 1''''; crests variable, entire to denticulate, rarely spiny. Cingulum displaced up to two cingular widths, distinct; reflected sulcal tabulation absent but sulcal region distinct.
Dimensions: Holotype: Periblast length 125 µm, width 95µm; endoblast length 74 µm. Range: Periblast length 93-135 µm; apical horn 20-33 µm; endoblast length 63-100 µm; endoblast horn 3-9 µm; periblast width 40-83µm. 25 specimens measured.
For an elaborate description see Brideaux and Fisher, 1976, p. 18-19
Affinities:
Brideaux and Fisher, 1976, p. 19 : Psaligonyaulax dualis
P. dualis differs from previously published species of the genus in the following ways: from P. deflanfrei Sarjeant by its larger size, more prominent apical horn, rhombic endoblast and details of tabulation; from P. apatela (Cookson and Eisenack) Sarjeant in overal shape, greater overall length and length of apical horn, type of sutural crests, shape of the endophragm, and details of tabulation; and from P. simplicia (Cookson and Eisenack) Sarjeant in shape, form of sutures, details of tabulation, and other features. P. dualis bears a superficial similarity to Gonyaulacacysta jurassica (Deflandre) Norris and Sarjeant, but differs in at least four features. The size of the periblast and endoblast is generally larger, the smaller specimens of P. dualis overlapping only with the largest speicmens of G. jurassica; P. dualis has well-developed apical and antapical pericoels; specimens with a pronounced apical pericoel assigned to G. jurassica by Sarjeant differ in that the pericoel is formed by broadening of the apical horn at its base. P. dualis has a consistently well-developed antapical breach in the periblast, and more rarely, an antapical bulge. Finally, the endoblast of P. dualis exhibits a consistently rhombic outline.
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Emended description Riding et al., 2022:
Emended diagnosis: A large, elongate, bicavate species of Gonyaulacysta with a prominent apical horn formed of periphragm and a marked apical protuberance on the endocyst. Most of the sutural features are smooth ridges, but sporadically denticulate sutural crests and ridges may be developed. The sulcus is L-type and longitudinal.
Emended description: A large, elongate species of Gonyaulacysta with a bicavate cyst. Some of the precingular and postcingular plate boundaries may exhibit suturocavation. The epipericoel and hypopericoel are both large. It has a long, slender, distally truncate apical horn composed of periphragm. The endocyst exhibits a prominent rounded apical protuberance which may attain 8 μm in height. The tabulation comprises sutural ridges or crests that are usually low and distally smooth. However, these sutural features may bear small, pointed denticles. Denticulate sutural crests/ridges typically occur around the cingulum, in the lateral regions and rarely surrounding the 1′′′′ plate. Additionally, the antapical plate may bear relatively prominent gonal spines up to 5 μm in length. The longitudinal L-type sulcus and an opisthopyle are usually evident; the latter is subcircular to ellipsoidal and varies greatly in size. The periphragm may be smooth to markedly scabrate; the thicker endophragm is consistently smooth. The periarchaeopyle is large and may extend above the top of the endocyst.
Holotype: Brideaux and Fisher (1976, pl. 1, 4–5). Geological Survey of Canada (GSC) type number 34154; GSC location number C-12532, slide P810-13B. Ditch cuttings sample from the Gilmore LakeMember of the Langton Bay Formation, (upper Oxfordian–middle Kimmeridgian) between 552 m and 549 m in the Elf Horton River G-02 well, District of Mackenzie (now Northwest Territories), Canada. Specimen curated in the National Collection of Type Invertebrate and Plant Fossils, GSC, Ottawa, Ontario, Canada. At the time of writing, the specimen is on longterm loan to GSC Calgary.
Comments: This species was established by Brideaux and Fisher (1976) as Psaligonyaulax dualis, and transferred to Gonyaulacysta by Stover and Evitt (1978, p. 158). Psaligonyaulax has an equatorial cingulum and does not exhibit an opisthopyle (Sarjeant, 1966, fig. 35). Sarjeant (1982, p. 29) considered Psaligonyaulax dualis to be a taxonomic junior synonym of Gonyaulacysta jurassica, but Jan du Chêne et al. (1986, p. 131) retained Gonyaulacysta dualis as a separate species. Gonyaulacysta dualis is emended herein to stress its large size, slender and elongate outline, bicavate cyst organisation, prominent apical horn, and largely distally smooth sutures. Also highly distinctive is the long, thin apical horn, which has the form of an elongate and distally truncated cone. This feature ismirrored by a prominent apical protuberance on the endocyst. Gonyaulacysta dualis is bicavate, with large polar pericoels. Sutural features are usually low, distally smooth ridges, but low, occasionally denticulate crests may be developed (Brideaux and Fisher, 1976, pl. 1, 9–11). Other features that may be present are gonal spines around the 1′′′′ plate, and a scabrate periphragm (Plate VIII). Sarjeant (1982, p. 31–32; pl. 5, 5, 6) established Gonyaulacysta jurassica subsp. jurassica var. longicornuta. The single specimen figured by Sarjeant (1982) is virtually identical in all respects to the holotype of Gonyaulacysta dualis. Hence it is clear that Gonyaulacysta jurassica subsp. jurassica var. longicornuta is a taxonomic junior synonymof Gonyaulacysta dualis. We consider that the specimen illustrated as Gonyaulacysta dualis by Burger (1996, pl. 6W) is a misidentification of Gonyaulacysta jurassica.
Comparison: The most similar species to Gonyaulacysta dualis is Gonyaulacysta longicornis (not to be confused with Gonyaulacysta jurassica subsp. jurassica var. longicornuta of Sarjeant, 1982). However Gonyaulacysta longicornis is epicavate and has highly denticulate sutural crests. Gonyaulacysta dualis is also morphologically close to Gonyaulacysta ceratophora and Gonyaulacysta jurassica. However, Gonyaulacysta ceratophora lacks full tabulation and Gonyaulacysta jurassica is characterised by sutural crests which are high and densely denticulate (Fig. 2).
Dimensions: Gonyaulacysta dualis is a large species; the dimensions of the material from Alaska studied herein based on 30 specimens are: length of pericyst, 93 (109) 122; length of apical horn, 20 (28) 38; length of epipericyst, 53 (66) 75; length of hypopericyst, 22 (36) 49; length of endocyst, 62 (73) 91; width at cingulum, 55 (70) 80 (Supplementary material Appendix 3, table 9). This compares well with measurements of the type material by Brideaux and Fisher (1976, p. 19): length of pericyst, 93–135; length of apical horn, 20–33; length of endocyst, 63–100; length of protuberance on the endocyst, 3–9; width at cingulum, 40–83.
Geographical and stratigraphical distribution: Gonyaulacysta dualis is largely confined to the Oxfordian and Kimmeridgian (Late Jurassic) of the high palaeolatitudes of North America. The stratigraphical extent of the original material from Arctic Canada is upper Oxfordian to middle Kimmeridgian (Brideaux and Fisher, 1976, p. 19–20, fig. 13). These authors stated that the species is sporadic in the upper Kimmeridgian. Riding and Lucas-Clark (2016, pl. 2, 2; pl. 16, 4–6) figured specimens of Gonyaulacysta dualis from the Oxfordian of southwestern Alaska. This species was also recorded from the upper Oxfordian to upper Kimmeridgian, and the Oxfordian to middle Kimmeridgian of the Sverdrup Basin, Arctic Canada by Tan and Hills (1978) and Davies (1983) respectively. It was also recorded by Sarjeant (1982) from the lower to middle Kimmeridgian of northern Canada. Brideaux and Fisher (1976, p. 19) stated that some specimens of Gonyualacysta longicornis from Europe closely resemble Gonyaulacysta dualis. However, in our view, the specimens figured by Klement (1960, pl. 2, 6–8), Sarjeant (1962, pl.1, 3) and Gitmez (1970, pl. 5, 11) have prominent denticulate sutural crests and are epicavate, and hence do not belong to Gonyaulacysta dualis. Likewise, we believe that the specimens of Gonyaulacysta dualis figured by Brenner (1988, pl. 8, 2, 5), with their high, denticulate sutural crests, relatively short apical horns, and lack of apical protuberances on the endocyst, belong to Gonyaulacysta jurassica. Riding et al. (1999, pl. RP8, 5; pl. RP9, 2, 3, 6) figured specimens assigned to Gonyaulacysta dualis from the middle and upper Oxfordian of the Russian Platform. However, these specimens are epicavate, lack a well-developed apical protuberance on the endocyst, and the specimens on plate RP9 lack obvious tabulation in the equatorial area; hence they do not belong to Gonyaulacysta dualis. The only positive identification of Gonyaulacysta dualis from Europe is a specimen illustrated from the lowermost Kimmeridgian of Denmark by Poulsen (1996, pl. 4, 1).
Cookson and Eisenack (1982, p. 37–38) described Psaligonyaulax australica from the upper part of the Dingo Claystone of the Carnarvon Basin of Western Australia (Oxfordian to lower Kimmeridgian). Brenner (1988, p. 54) stated that Psaligonyaulax australica is a junior synonym of Gonyaulacysta dualis. The holotype of Psaligonyaulax australica is large, elongate, and has largely smooth sutural ridges, and so is somewhat similar in morphology to Gonyaulacysta dualis and has a similar stratigraphical range. However, the apical horn of Psaligonyaulax australica is smaller than is normal for Gonyaulacysta dualis, and the former has a semicircular hypocyst. Thus, we do not follow the synonymy proposed by Brenner (1988). Psaligonyaulax australica is herein transferred to Gonyaulacysta (see this section, above).