Back
Gonyaulacysta desmos
Original description (Poulsen, 1991):
Gonyaulacysta jurassica (Deflandre 1938) desmos subsp. nov.
Plate 1, figs. 3, 6
Gonyaulacysta jurassica (Deflandre 1938) emend. Norris & Sarjeant 1965 emend. Sarjeant, 1982; Sarjeant, 1982, text-fig. 2a, pl. 4, fig. 8, pl. 5, fig. 1.
Derivation of Name. Greek Seguos (desmos), link, (transitional form).
Diagnosis. A subspecies of Gonyaulacysta jurassica which exhibits only partial development of the hypopericoel, i.e., there is a marginal separation of the hypoperiphragm and hypoendophragm, whereas the two wall layers are in contact at the mid-antapical region.
Holotype. Oxford Clay (1 m below the Lower Calcareous Grit Formation) Cayton Bay, Yorkshire, DGU Catalogue No.: 1989-NEP-1.
Paratype. Oxford Clay (27 m below the Lower Calcareous Grit Formation) Cayton Bay, Yorkshire, DGU Catalogue No.: 1989-NEP-2.
Occurrence. Praecordatum, Bukowskii and Costicardia ammonite subzones of the early Oxfordian in England.
Discussion. Gonyaulacysta jurassica desmos subsp. nov. appears to be a transitional form between the subspecies G.jurassica adecta, which has an acavate hypocyst, and the subspecies G. jurassica jurassica which has a well developed hypopericoel. The new subspecies of G. jurassica is proposed because itis morphologically distinct and it has potential stratigraphic significance. All three subspecies occur together in the early Oxfordian.
STRATIGRAPHIC DISTRIBUTION
In Europe, Gonyaulacysta jurassica first appears in the early Bathonian (Woollam and Riding, 1983; Riding et al., 1985; Davies, 1985; Herngreen and de Boer, 1978). In East Greenland, Svalbard, and Franz Josef Land, the first appearance of Gonyaulacysta jurassica is in the Callovian (Bjaerke, 1980; Piasecki 1980; Smelror, 1987; 1988 a, b). In the Sverdrup Basin the first appearance of G. jurassica was also reported as Callovian (Johnson and Hills, 1973) or late Bathonian to early Callovian (Davies, 1983). Sarjeant (1982) determined that the earliest occurrences of G. jurassica are restricted to the subspecies adecta. G. jurassica jurassica first appears in the carly Oxfordian (Sarjeant, 1982: Riding, 1984).
The first appearance of Gonyaulacysta jurassica desmos (Text-Figure 3) was reported by Sarjeant (1982, p. 14), as the Praecordatum ammonite Subzone of the Mariae ammonite Zone (early Oxfordian) in his discussion of the development of hypopericoel in G. jurassica. The first appearance of G. jurassica desmos as reported herein also occurs in the Praecordatum ammonite Subzone. In East Greenland the range base occurs just above the first ap- pearance of Wanaea fimbriata, the inception of which marks the base of the Mariae ammonite Zone (early Oxfordian) (see Woollam and Riding, 1983; Riding, 1984).
The extinction of Gonyaulacysta jurassica desmos in England is within the Bukowskii ammonite Subzone of the Cordatum ammonite Zone (early Oxfordian). However, one poorly preserved specimen has been recorded in the overlying Costicardia ammonite Subzone (Upper Oxford Clay, Ham Cliff). The last appearance of G. jurassica adecta is in the late Oxfordian, Regulare ammonite Zone (Thomas and Cox, 1988).
The illustration of Gonyaulacysta jurassica jurassica from the Regulare ammonite Zone (late Oxfordian) provided by Riding (1984, fig. 4.6: 1987, fig. 8.8) shows similarities to G. jurassica desmos. The posterior part of the endophragm. however, is not in sharp focus and is not in contact with the periphragm (Riding, written commun.,1988).
The range top of Gonyaulacysta jurassica jurassica seems to vary geographically. In Poland the last Occurrence is in the Autissiodonensis Zone (latest Kimmeridgian) (unpubl. data of the present author). In Britain, the extinction is reported (Woollam and Riding, 1983; Riding, 1984) to be within the Pectinatus ammonite Zone (latest early Volgian).
------------------------------------------------------------------------------------------
Emended description Riding et al., 2022:
Emended diagnosis: A subpentagonal, cornucavate species of Gonyaulacysta with a prominent apical horn, a longitudinal L-type sulcus and a partially developed hypopericoel. Most of the sutural features are echinate crests. The periphragm is smooth to microscabrate and the endophragm is smooth.
Emended description: A subpentagonal species of Gonyaulacysta that is intermediate in size and may be somewhat squat or elongate. The epicyst is cornucavate, and a hypopericoel is partially developed: in the antapical area, the endophragm and periphragmare in contact centrally, but separated laterally by up to 7 μm. This partial cavation in the hypocyst makes the antapical margin markedly concave. The species has a well-developed apical horn, composed of periphragm, that is usually relatively slender and consistently truncate distally. The endocyst is ovoidal and lacks an apical protuberance. The laevorotatory nature of the cingulum is marked. The sulcus is of L-type and longitudinal. The tabulation is reflected by distally echinate sutural ridges or crests that vary in height. The 1′′′′ plate may bear relatively small gonal spines 3–9 μm high. The periphragm is smooth or sometimes microscabrate; the endophragm is smooth. An opisthopyle has not been observed in this species.
Holotype: Specimen DGU catalogue number 1989-NEP-1 (Poulsen, 1991, figs. 1, 2; pl. 1, 3). Sample from the Oxford Clay Formation (lower Oxfordian, Quenstedtocerasmariae ammonite zone) froma horizon 1 m below the base of the Lower Calcareous Grit Formation, at Cayton Bay, North Yorkshire, UK. Curated in the Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark.
Comments: Gonyaulacysta desmos was originally described by Poulsen (1991) as a subspecies of Gonyaulacysta jurassica. The epithet desmos derives fromthe Greek for link, and is in reference to the transitional morphology of this taxon. Poulsen (1991, fig. 3) envisaged his Gonyaulacysta jurassica subsp. desmos as an intermediate morphotype between Gonyaulacysta jurassica subsp. adecta and Gonyaulacysta jurassica subsp. jurassica. The partially developed hypopericoel (Sarjeant, 1982, fig. 2a) is transitional between Gonyaulacysta jurassica subsp. adecta (cornucavate or epicavate), and Gonyaulacysta jurassica subsp. jurassica (bicavate or delphicavate), i.e. between Gonyaulacysta adecta and Gonyaulacysta jurassica as defined herein. This interpretation is supported, in a strictly phylogenetic sense, by the stratigraphical position of Gonyaulacysta desmos near the inception of Gonyaulacysta jurassica subsp. jurassica (Poulsen, 1991, fig. 3). This taxon is emended herein to note the cornucavate epicyst, echinate sutural crests, substantially laevorotatory cingulum, occasionally microscabrate periphragm, and prominent apical horn, as well as the cyst's shape and size.
Comparison: Gonyaulacysta desmos is morphologically transitional between Gonyaulacysta adecta and Gonyaulacysta jurassica in having a partially developed hypopericoel.
Dimensions: Gonyaulacysta desmos is a relatively rare species; only seven specimens were analysed in this study. The dimensions are: length of pericyst, 64 (74) 84; length of apical horn, 11 (14) 16; length of epipericyst, 31 (38) 44; length of hypopericyst, 27 (31) 40; length of endocyst, 44 (51) 64; width at cingulum, 42 (51) 69 (Supplementary material Appendix 3, table 8). The overall length of the holotype and the paratype are 93 μm and 74 μm respectively (Poulsen, 1991). The size of the paratype is similar to the dimensions of the material studied herein.
Geographical and stratigraphical distribution: Gonyaulacysta desmos has only been recorded from the lower Oxfordian of northwestern Europe, East Greenland and the USA. In England, this species is confined to the Cardioceras praecordatum, Cardioceras bukowskii and Cardioceras costicardia ammonite subzones (Quenstedtoceras mariae and Caradioceras cordatum ammonite zones) of the lower Oxfordian according to Poulsen (1991). Gonyaulacysta desmos has also been recorded from the lower Oxfordian of East Greenland (Poulsen, 1991), and Colorado and Utah, USA (Riding, 2016).
Gonyaulacysta jurassica (Deflandre 1938) desmos subsp. nov.
Plate 1, figs. 3, 6
Gonyaulacysta jurassica (Deflandre 1938) emend. Norris & Sarjeant 1965 emend. Sarjeant, 1982; Sarjeant, 1982, text-fig. 2a, pl. 4, fig. 8, pl. 5, fig. 1.
Derivation of Name. Greek Seguos (desmos), link, (transitional form).
Diagnosis. A subspecies of Gonyaulacysta jurassica which exhibits only partial development of the hypopericoel, i.e., there is a marginal separation of the hypoperiphragm and hypoendophragm, whereas the two wall layers are in contact at the mid-antapical region.
Holotype. Oxford Clay (1 m below the Lower Calcareous Grit Formation) Cayton Bay, Yorkshire, DGU Catalogue No.: 1989-NEP-1.
Paratype. Oxford Clay (27 m below the Lower Calcareous Grit Formation) Cayton Bay, Yorkshire, DGU Catalogue No.: 1989-NEP-2.
Occurrence. Praecordatum, Bukowskii and Costicardia ammonite subzones of the early Oxfordian in England.
Discussion. Gonyaulacysta jurassica desmos subsp. nov. appears to be a transitional form between the subspecies G.jurassica adecta, which has an acavate hypocyst, and the subspecies G. jurassica jurassica which has a well developed hypopericoel. The new subspecies of G. jurassica is proposed because itis morphologically distinct and it has potential stratigraphic significance. All three subspecies occur together in the early Oxfordian.
STRATIGRAPHIC DISTRIBUTION
In Europe, Gonyaulacysta jurassica first appears in the early Bathonian (Woollam and Riding, 1983; Riding et al., 1985; Davies, 1985; Herngreen and de Boer, 1978). In East Greenland, Svalbard, and Franz Josef Land, the first appearance of Gonyaulacysta jurassica is in the Callovian (Bjaerke, 1980; Piasecki 1980; Smelror, 1987; 1988 a, b). In the Sverdrup Basin the first appearance of G. jurassica was also reported as Callovian (Johnson and Hills, 1973) or late Bathonian to early Callovian (Davies, 1983). Sarjeant (1982) determined that the earliest occurrences of G. jurassica are restricted to the subspecies adecta. G. jurassica jurassica first appears in the carly Oxfordian (Sarjeant, 1982: Riding, 1984).
The first appearance of Gonyaulacysta jurassica desmos (Text-Figure 3) was reported by Sarjeant (1982, p. 14), as the Praecordatum ammonite Subzone of the Mariae ammonite Zone (early Oxfordian) in his discussion of the development of hypopericoel in G. jurassica. The first appearance of G. jurassica desmos as reported herein also occurs in the Praecordatum ammonite Subzone. In East Greenland the range base occurs just above the first ap- pearance of Wanaea fimbriata, the inception of which marks the base of the Mariae ammonite Zone (early Oxfordian) (see Woollam and Riding, 1983; Riding, 1984).
The extinction of Gonyaulacysta jurassica desmos in England is within the Bukowskii ammonite Subzone of the Cordatum ammonite Zone (early Oxfordian). However, one poorly preserved specimen has been recorded in the overlying Costicardia ammonite Subzone (Upper Oxford Clay, Ham Cliff). The last appearance of G. jurassica adecta is in the late Oxfordian, Regulare ammonite Zone (Thomas and Cox, 1988).
The illustration of Gonyaulacysta jurassica jurassica from the Regulare ammonite Zone (late Oxfordian) provided by Riding (1984, fig. 4.6: 1987, fig. 8.8) shows similarities to G. jurassica desmos. The posterior part of the endophragm. however, is not in sharp focus and is not in contact with the periphragm (Riding, written commun.,1988).
The range top of Gonyaulacysta jurassica jurassica seems to vary geographically. In Poland the last Occurrence is in the Autissiodonensis Zone (latest Kimmeridgian) (unpubl. data of the present author). In Britain, the extinction is reported (Woollam and Riding, 1983; Riding, 1984) to be within the Pectinatus ammonite Zone (latest early Volgian).
------------------------------------------------------------------------------------------
Emended description Riding et al., 2022:
Emended diagnosis: A subpentagonal, cornucavate species of Gonyaulacysta with a prominent apical horn, a longitudinal L-type sulcus and a partially developed hypopericoel. Most of the sutural features are echinate crests. The periphragm is smooth to microscabrate and the endophragm is smooth.
Emended description: A subpentagonal species of Gonyaulacysta that is intermediate in size and may be somewhat squat or elongate. The epicyst is cornucavate, and a hypopericoel is partially developed: in the antapical area, the endophragm and periphragmare in contact centrally, but separated laterally by up to 7 μm. This partial cavation in the hypocyst makes the antapical margin markedly concave. The species has a well-developed apical horn, composed of periphragm, that is usually relatively slender and consistently truncate distally. The endocyst is ovoidal and lacks an apical protuberance. The laevorotatory nature of the cingulum is marked. The sulcus is of L-type and longitudinal. The tabulation is reflected by distally echinate sutural ridges or crests that vary in height. The 1′′′′ plate may bear relatively small gonal spines 3–9 μm high. The periphragm is smooth or sometimes microscabrate; the endophragm is smooth. An opisthopyle has not been observed in this species.
Holotype: Specimen DGU catalogue number 1989-NEP-1 (Poulsen, 1991, figs. 1, 2; pl. 1, 3). Sample from the Oxford Clay Formation (lower Oxfordian, Quenstedtocerasmariae ammonite zone) froma horizon 1 m below the base of the Lower Calcareous Grit Formation, at Cayton Bay, North Yorkshire, UK. Curated in the Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark.
Comments: Gonyaulacysta desmos was originally described by Poulsen (1991) as a subspecies of Gonyaulacysta jurassica. The epithet desmos derives fromthe Greek for link, and is in reference to the transitional morphology of this taxon. Poulsen (1991, fig. 3) envisaged his Gonyaulacysta jurassica subsp. desmos as an intermediate morphotype between Gonyaulacysta jurassica subsp. adecta and Gonyaulacysta jurassica subsp. jurassica. The partially developed hypopericoel (Sarjeant, 1982, fig. 2a) is transitional between Gonyaulacysta jurassica subsp. adecta (cornucavate or epicavate), and Gonyaulacysta jurassica subsp. jurassica (bicavate or delphicavate), i.e. between Gonyaulacysta adecta and Gonyaulacysta jurassica as defined herein. This interpretation is supported, in a strictly phylogenetic sense, by the stratigraphical position of Gonyaulacysta desmos near the inception of Gonyaulacysta jurassica subsp. jurassica (Poulsen, 1991, fig. 3). This taxon is emended herein to note the cornucavate epicyst, echinate sutural crests, substantially laevorotatory cingulum, occasionally microscabrate periphragm, and prominent apical horn, as well as the cyst's shape and size.
Comparison: Gonyaulacysta desmos is morphologically transitional between Gonyaulacysta adecta and Gonyaulacysta jurassica in having a partially developed hypopericoel.
Dimensions: Gonyaulacysta desmos is a relatively rare species; only seven specimens were analysed in this study. The dimensions are: length of pericyst, 64 (74) 84; length of apical horn, 11 (14) 16; length of epipericyst, 31 (38) 44; length of hypopericyst, 27 (31) 40; length of endocyst, 44 (51) 64; width at cingulum, 42 (51) 69 (Supplementary material Appendix 3, table 8). The overall length of the holotype and the paratype are 93 μm and 74 μm respectively (Poulsen, 1991). The size of the paratype is similar to the dimensions of the material studied herein.
Geographical and stratigraphical distribution: Gonyaulacysta desmos has only been recorded from the lower Oxfordian of northwestern Europe, East Greenland and the USA. In England, this species is confined to the Cardioceras praecordatum, Cardioceras bukowskii and Cardioceras costicardia ammonite subzones (Quenstedtoceras mariae and Caradioceras cordatum ammonite zones) of the lower Oxfordian according to Poulsen (1991). Gonyaulacysta desmos has also been recorded from the lower Oxfordian of East Greenland (Poulsen, 1991), and Colorado and Utah, USA (Riding, 2016).