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Dracodinium robertknoxii
from Iakovleva and Heilmann-Clausen, 2021
Dracodinium robertknoxii sp. nov. Plate 6, figures 1–4
Synonymy. Dracodinium sp. 1 in Heilmann-Clausen and Costa, 1989, pl. 1, figs 1, 2; Dracodinium sp. 1 in Iakovleva and Heilmann-Clausen, 2010, pl. 5, fig. 1.
Holotype. Slide 2826-F2, England Finder coordinates C25; MGUH 32065.
Paratype. Slide 2809-E1, England Finder coordinates S44/1; MGUH 32066.
Type stratum and locality. Sample 9.45 m, Alashen Formation, Aktulagay outcrop section, Kazakhstan.
Diagnosis. A circumcavate to cornucavate peridinioid cystwith a pericyst which is broadly square-shaped, reduced apical pericoel and poorly developed lateral and antapical horns.
Description. A circumcavate to cornucavate wetzelielloidean cyst with a rounded square-shaped to subcircular ambitus of the pericyst. The apical horn is rounded and weakly developed or entirely absent. Occasionally the pericoel in the apical zone may be completely invisible. The lateral
horns are short and greatly reduced. The lengths of the epipericyst and hypopericyst are almost equal. In the antapical region the pericyst usually forms a slightly toothed swelling with a weak initiation of only the left antapical horn. The endocyst is circular in ambitus. The endophragm is relatively smooth and the periphragm is slightly chagrinate. The paratabulation is indeterminate. The pericingulum may be expressed only at the extremities of the lateral horns. The archeopyle is intercalary and corresponds to paraplate 2a.
Dimensions. Holotype: pericyst length 102 µm; pericyst width 110 µm; endocyst length 78 µm; endocyst width 80 µm. Paratype: pericyst length 89 µm; pericyst width 93 µm; endocyst length 69 µm; endocyst width 78 µm. Dimensions of measured specimens: pericyst length 81–114 µm (mean 95 µm); pericyst width 84–114 µm (mean 97 µm); endocyst length 65–87 µm (mean 76 µm); endocyst width 66–84 µm (mean 75 µm); 16 specimens measured.
Comparison. Dracodinium robertknoxii sp. nov. differs from the type species (Dr. condylos) by the absence of the intratabular ornamentation and by the extremely short and blunt lateral horns. It also differs from two closely related species, Dracodinium laszczynskii Gedl 1995 and Dracodinium waipawaense (Wilson 1967) Costa and Downie 1979, by a less developed or almost absent apical pericoel and horn, and less developed (or even absent) lateral horns, by a more cornucavate than circumcavate pericyst, and by the slightly chagrinate periphragm.
Discussion. The new wetzelielloidean systematics proposed by Williams et al. (2015) is based primarily on the archeopyle type and only secondarily on the wall morphology and ornamentation. One of us (Iakovleva 2017a) has already applied this new systematics in the description of 14 new earliest Eocene species. In the morphologic study of Dracodinium robertknoxii sp. nov. we also tried to clearly recognize the archeopyle type of this new taxon according to the systematic concepts of Williams et al. (2015). However, we ran into a problem with correctly identifying the archeopyle of Dracodinium robertknoxii sp. nov. The holotype of this species (Plate 6, figure 4) seems to have an equiepeliform archeopyle; and its paratype (Plate 6, figure 3) has either an equiepeliform or hyperepeliform archeopyle. The specimen illustrated in Plate 6, figure 1, however, seems to demonstrate the latiepeliform archeopyle, while the archeopyle of the specimen in Plate 6, figure 2 is not clearly recognizable. Additionally, the specimen of Dracodinium robertknoxii sp. nov. from Western Siberia, published as Dracodinium sp. 1 (pl. 5, fig. 1 in Iakovleva and Heilmann-Clausen 2010) also seems to have a latiepeliform archeopyle. The first specimen, also published as Dracodinium sp. 1 from the NW Germany (pl. 1, fig. 1 in Heilmann-Clausen and Costa 1989), seems to have an equiepeliform archeopyle, while the second one (pl. 1, fig. 2 in Heilmann-Clausen and Costa 1989) more likely has a latiepeliform archeopyle. This variability in archeopyle geometry requires without doubt additional investigations both for Dracodinium robertknoxii sp. nov. and for the wetzelielloidean taxa in general, and will be considered in future publications.
Stratigraphic range. Mid-upper Ypresian.
Derivation of name. In honor of the late British geologist Robert W.O’B. Knox.
Dracodinium robertknoxii sp. nov. Plate 6, figures 1–4
Synonymy. Dracodinium sp. 1 in Heilmann-Clausen and Costa, 1989, pl. 1, figs 1, 2; Dracodinium sp. 1 in Iakovleva and Heilmann-Clausen, 2010, pl. 5, fig. 1.
Holotype. Slide 2826-F2, England Finder coordinates C25; MGUH 32065.
Paratype. Slide 2809-E1, England Finder coordinates S44/1; MGUH 32066.
Type stratum and locality. Sample 9.45 m, Alashen Formation, Aktulagay outcrop section, Kazakhstan.
Diagnosis. A circumcavate to cornucavate peridinioid cystwith a pericyst which is broadly square-shaped, reduced apical pericoel and poorly developed lateral and antapical horns.
Description. A circumcavate to cornucavate wetzelielloidean cyst with a rounded square-shaped to subcircular ambitus of the pericyst. The apical horn is rounded and weakly developed or entirely absent. Occasionally the pericoel in the apical zone may be completely invisible. The lateral
horns are short and greatly reduced. The lengths of the epipericyst and hypopericyst are almost equal. In the antapical region the pericyst usually forms a slightly toothed swelling with a weak initiation of only the left antapical horn. The endocyst is circular in ambitus. The endophragm is relatively smooth and the periphragm is slightly chagrinate. The paratabulation is indeterminate. The pericingulum may be expressed only at the extremities of the lateral horns. The archeopyle is intercalary and corresponds to paraplate 2a.
Dimensions. Holotype: pericyst length 102 µm; pericyst width 110 µm; endocyst length 78 µm; endocyst width 80 µm. Paratype: pericyst length 89 µm; pericyst width 93 µm; endocyst length 69 µm; endocyst width 78 µm. Dimensions of measured specimens: pericyst length 81–114 µm (mean 95 µm); pericyst width 84–114 µm (mean 97 µm); endocyst length 65–87 µm (mean 76 µm); endocyst width 66–84 µm (mean 75 µm); 16 specimens measured.
Comparison. Dracodinium robertknoxii sp. nov. differs from the type species (Dr. condylos) by the absence of the intratabular ornamentation and by the extremely short and blunt lateral horns. It also differs from two closely related species, Dracodinium laszczynskii Gedl 1995 and Dracodinium waipawaense (Wilson 1967) Costa and Downie 1979, by a less developed or almost absent apical pericoel and horn, and less developed (or even absent) lateral horns, by a more cornucavate than circumcavate pericyst, and by the slightly chagrinate periphragm.
Discussion. The new wetzelielloidean systematics proposed by Williams et al. (2015) is based primarily on the archeopyle type and only secondarily on the wall morphology and ornamentation. One of us (Iakovleva 2017a) has already applied this new systematics in the description of 14 new earliest Eocene species. In the morphologic study of Dracodinium robertknoxii sp. nov. we also tried to clearly recognize the archeopyle type of this new taxon according to the systematic concepts of Williams et al. (2015). However, we ran into a problem with correctly identifying the archeopyle of Dracodinium robertknoxii sp. nov. The holotype of this species (Plate 6, figure 4) seems to have an equiepeliform archeopyle; and its paratype (Plate 6, figure 3) has either an equiepeliform or hyperepeliform archeopyle. The specimen illustrated in Plate 6, figure 1, however, seems to demonstrate the latiepeliform archeopyle, while the archeopyle of the specimen in Plate 6, figure 2 is not clearly recognizable. Additionally, the specimen of Dracodinium robertknoxii sp. nov. from Western Siberia, published as Dracodinium sp. 1 (pl. 5, fig. 1 in Iakovleva and Heilmann-Clausen 2010) also seems to have a latiepeliform archeopyle. The first specimen, also published as Dracodinium sp. 1 from the NW Germany (pl. 1, fig. 1 in Heilmann-Clausen and Costa 1989), seems to have an equiepeliform archeopyle, while the second one (pl. 1, fig. 2 in Heilmann-Clausen and Costa 1989) more likely has a latiepeliform archeopyle. This variability in archeopyle geometry requires without doubt additional investigations both for Dracodinium robertknoxii sp. nov. and for the wetzelielloidean taxa in general, and will be considered in future publications.
Stratigraphic range. Mid-upper Ypresian.
Derivation of name. In honor of the late British geologist Robert W.O’B. Knox.