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Graptodinium
From Williams et al., 2017:
[Graptodinium, Clowes, 2013, p. 316–318.
Type species: Graptodinium inconditum, Clowes, 2013 (pl.1, figs.1–3)]
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Original description: [Clowes, 2013]:
Description:
Cysts small, proximate, subspherical to distinctly prolate, lacking horns; the epicyst slightly to considerably smaller than the hypocyst.
Cyst walls apparently single-layered, ornamented by numerous short, sutural crests and characteristic intratabular accessory crests.
Archaeopyle apical, type (tA); operculum free or attached; margin gently angular; sulcal notch shallow and often inconspicuous.
Processes lacking; ornament comprising low sutural and intratabular septa. Sutural septa clearly delineate a cladopyxiacean tabulation; formula ?4’, ?0a, 6’’, 6c, 6’’’, 1p, 1’’’’; the first postcingular plate is large and positioned outside the sulcus; torsion sinistral; hyposome partiform. Accessory septa forming an intratabular ornament, varying from discontinuous ridges and isolated granules, to a fully-developed reticulum.
Cingulum and sulcus usually clearly delineated by the sutural septa, although individual plates are difficult to separate consistently; cingulum variably subdivided into transversely elongate plates; the ends of the cingulum not perceptibly offset, but meeting the sulcus directly opposite one another; sulcus broadly aligned with the polar axis rather than oblique.
Remarks:
Graptodinium gen. nov. is represented by two species which appear to almost integrate in some samples. Some workers use the presence of intermediates to ‘lump’ taxa into a single species. However, the existence of intermediates, known or unknown, is normal. Except where lineages become extinct, morphological discontinuities are sampling artefacts; the presence or otherwise of known intermediates has no intrinsic phylogenetic meaning. Specifically, it is inappropriate to combine taxa simply because intermediates were observed, as opposed to being present in a sediment yet to be examined; synonymy requires stronger support than that. In general, the divisions between fossil morphotaxa are necessarily arbitrary, and the imprecision of gradational boundaries between taxa is unavoidable
Affinities:
Graptodinium gen. nov. has a single, large, six-sided antapical (1’’’’) plate. The posterior sulcal plate extends further to the anterior than the posterior intercalary plate (the partiform condition of Evitt 1985, p. 112; see Plate 2, figure 11 in the present paper), indicating that this form is a cladopyxiinean. The two genera which Graptodinium gen. nov. has previously been attributed to are Histiocysta and Microdinium, both of which exhibit a partiform hypocyst, and are also included in the Family Cladopyxiaceae (Fensome et al. 1993). Further morphological comparison with Histiocysta is difficult because the detailed morphology, particularly the tabulation pattern, of Histiocysta is rather poorly known. However, the Late Jurassic to Cretaceous range of Histiocysta, compared to the Eocene to Oligocene range of Graptodinium gen. nov., is pragmatically sufficient to avoid confusion. Stover and Evitt (1978, p. 65, 66) noted the occasional presence of anterior intercalary plates in Microdinium. Anterior intercalary plates have not been identified in Graptodinium gen. nov. If they are subsequently demonstrated to be present, Graptodinium gen. nov. may be a junior synonym of Microdinium. Other broadly similar proximate genera with an apical archaeopyle include Elytrocysta, Glyphanodinium and Meiourogonyaulax. Elytrocysta differs in lacking tabulation other than an occasional faint alignment of the ornament near the cingulum, and possibly by the possession of an ectophragm. Glyphanodinium has a five-sided, angular rather than rounded outline, lacks the intratabular ornament characteristic of Graptodinium gen. nov., is strongly dorsoventrally flattened and is quinqueform. Meiourogonyaulax is distinguished by the more strongly laevorotatory cingulum, a deep sulcal notch and a different stratigraphical range.
[Graptodinium, Clowes, 2013, p. 316–318.
Type species: Graptodinium inconditum, Clowes, 2013 (pl.1, figs.1–3)]
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Clowes, 2013]:
Description:
Cysts small, proximate, subspherical to distinctly prolate, lacking horns; the epicyst slightly to considerably smaller than the hypocyst.
Cyst walls apparently single-layered, ornamented by numerous short, sutural crests and characteristic intratabular accessory crests.
Archaeopyle apical, type (tA); operculum free or attached; margin gently angular; sulcal notch shallow and often inconspicuous.
Processes lacking; ornament comprising low sutural and intratabular septa. Sutural septa clearly delineate a cladopyxiacean tabulation; formula ?4’, ?0a, 6’’, 6c, 6’’’, 1p, 1’’’’; the first postcingular plate is large and positioned outside the sulcus; torsion sinistral; hyposome partiform. Accessory septa forming an intratabular ornament, varying from discontinuous ridges and isolated granules, to a fully-developed reticulum.
Cingulum and sulcus usually clearly delineated by the sutural septa, although individual plates are difficult to separate consistently; cingulum variably subdivided into transversely elongate plates; the ends of the cingulum not perceptibly offset, but meeting the sulcus directly opposite one another; sulcus broadly aligned with the polar axis rather than oblique.
Remarks:
Graptodinium gen. nov. is represented by two species which appear to almost integrate in some samples. Some workers use the presence of intermediates to ‘lump’ taxa into a single species. However, the existence of intermediates, known or unknown, is normal. Except where lineages become extinct, morphological discontinuities are sampling artefacts; the presence or otherwise of known intermediates has no intrinsic phylogenetic meaning. Specifically, it is inappropriate to combine taxa simply because intermediates were observed, as opposed to being present in a sediment yet to be examined; synonymy requires stronger support than that. In general, the divisions between fossil morphotaxa are necessarily arbitrary, and the imprecision of gradational boundaries between taxa is unavoidable
Affinities:
Graptodinium gen. nov. has a single, large, six-sided antapical (1’’’’) plate. The posterior sulcal plate extends further to the anterior than the posterior intercalary plate (the partiform condition of Evitt 1985, p. 112; see Plate 2, figure 11 in the present paper), indicating that this form is a cladopyxiinean. The two genera which Graptodinium gen. nov. has previously been attributed to are Histiocysta and Microdinium, both of which exhibit a partiform hypocyst, and are also included in the Family Cladopyxiaceae (Fensome et al. 1993). Further morphological comparison with Histiocysta is difficult because the detailed morphology, particularly the tabulation pattern, of Histiocysta is rather poorly known. However, the Late Jurassic to Cretaceous range of Histiocysta, compared to the Eocene to Oligocene range of Graptodinium gen. nov., is pragmatically sufficient to avoid confusion. Stover and Evitt (1978, p. 65, 66) noted the occasional presence of anterior intercalary plates in Microdinium. Anterior intercalary plates have not been identified in Graptodinium gen. nov. If they are subsequently demonstrated to be present, Graptodinium gen. nov. may be a junior synonym of Microdinium. Other broadly similar proximate genera with an apical archaeopyle include Elytrocysta, Glyphanodinium and Meiourogonyaulax. Elytrocysta differs in lacking tabulation other than an occasional faint alignment of the ornament near the cingulum, and possibly by the possession of an ectophragm. Glyphanodinium has a five-sided, angular rather than rounded outline, lacks the intratabular ornament characteristic of Graptodinium gen. nov., is strongly dorsoventrally flattened and is quinqueform. Meiourogonyaulax is distinguished by the more strongly laevorotatory cingulum, a deep sulcal notch and a different stratigraphical range.