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Phthanoperidinium paleocenicum
Phthanoperidium paleocenicum Lucas-Clark, 2006, p.196,198, pl.2, figs.10–17; pl.3, figs.1–3; text-figs.5A–B.
Holotype: Lucas-Clark, pl.2, figs.10–12.
Age: Paleocene.
Original description (Lucas-Clark, 2006)
Holotype. Plate 2, figs. 10–12. South Carolina, Savannah River Site, core C-10,211.3–210.0m, sample 9202.224, slide cg no. 2 of 2, CGS Zeiss Sh., coordinates 100.1 × 16.1, England Finder reference Q37/3. Carnegie Museum of Natural History CM 19151.
Derivation of name. After the Paleocene; no species of Phthanoperidinium have hitherto been described from the Paleocene.
Diagnosis. Highly variable, small to medium, pale peridinioid with tabulation variously expressed by low ridges, lineations, or lines of beads along sutures. Circular to ovoidal to rectangular/peridinioid in shape. Sometimes with scattered granules. Archeopyle 2a, always with accessory sutures on either side of 4″. Distinguished by variable expression of tabulation and archeopyle with accessory sutures.
Description. Small to medium, proximate, peridiniacean, cornucavate cysts, slightly dorsoventrally compressed, with a short apical horn and two unequally developed, short antapical horns. Right antapical horn shorter and less well developed than the left. Endophragm smooth, thicker than periphragm, appressed to periphragm except beneath horns and some sutural ridges. Endocyst circular to ovoidal to slightly peridinioid in outline, often with flat antapical margin; Pericyst peridinioid in shape with slightly angular outline due to sutural ridges or rounded peridinioid, or nearly circular. Lateral margins angular to smoothly convex; antapical margin curved concave to nearly flat. Periphragm thin, ornamented with low sutural ridges, or alternatively with sutures outlined by granules, ‘beads’ that may be small and faint or larger (verrucate), or by some combination of ridges and ‘beads’. Periphragm otherwise smooth or ornamented with a few or many pustules or granules which may be partly penitabular or random. Nearly complete tabulation expressed by ridges or beads along sutures; some sulcal sutures suppressed. Tabulation formula 4′, 3a, 7″, 5c, 5′″, 1as, 1ps, 2″″. First apical plate (1′) broadly spatulate and indented on the posterior edge where it is in contact with a camerate or arched anterior sulcal plate (as). Ornament on the first apical plate sometimes suggests a plate division at the camerate peak of the anterior sulcal plate. Archeopyle intercalary, type I/I (2a) or occasionally I+P by the loss of both 2a and 4″; accessory archeopyle sutures usually present on 3″/4″ and 4″/5″ sutures. Plate 2a operculum free, iso- to eurydeltaform. One archeopyle appears to penetrate both wall layers. Cingulum indicated by transverse parallel ridges that are sometimes surmounted with beads, and by local concavity; subdivided in some specimens into at least 5 plates by sutural ridges. Sulcus expressed by a depression in the ventral hypocyst and outlined by ridges so that the partial tabulation (anterior sulcal and posterior sulcal) can be interpreted, although individual sutures within the sulcal region are suppressed.
Dimensions. Length, 55–65 μm; width, 35–45 μm (10 specimens measured).
Remarks. In this species, the anterior sulcal plate is apparently camerate as if in contact with two, rather than one apical plate (1′). In some cases a suggestion of a partial suture dividing the first apical plate is present. However, such a departure from the usual peridinioid tabulation pattern is so unusual and seemingly unlikely that it is interpreted as an unusual shape for both the anterior sulcal and the first apical plates. The high degree of morphological variability, especially in terms of the expression of the tabulation (outline by ridges, large beads, small beads or combination) provides possibilities of attempting to subdivide this species, possibly into two or more subspecies. However, the end members often occur in the same sample, and no stratigraphic or biogeo-graphic evidence supports the designation of another species, or of subspecies. The holotype and paratype represent the most common morphological variants of this species. Other specimens illustrated represent less common, but persistent forms.
Comparison. Phthanoperidinium paleocenicum sp.nov. differs from most other species of this genus in having a more clear lyperidinioid shape with definite antapical horns. Of species reportedly with 2 antapical horns, it lacks the gonal spines of Phthanoperidinium alectrolophum, the sutural spines of Phthanoperidinium echinatum, the high sutural crests of Phthanoperidinium levimurum, and the hairs and branched appendages of Phthanoperidinium comatum. Phthanoperidinium paleocenicum sp. nov. resembles Phthanoperidinium brooksii, but apparently lacks the cancellous filling between walls, has more prominent antapical horns, is less ovoidal in shape, and does not vary in archeopyle type to encompass 3 intercalaries and/or 3 precingulars. Phthanoperidinium paleocenicum sp. nov. bears a strong general resemblance to Phthanoperidinium? eocenicum and its possible junior synonym Phthanoperidinium resisente, but clearly has two antapical horns rather than one or none, and has accessory archeopyle sutures around plate 4″.
Previously Reported Occurrence. Paleocene, Lower Bridge Member of the Williamsburg Formation (NP3, 4, or 5), Black Mingo Group of Berkeley County, South Carolina; Paleocene (Danian), Brightseat Formation of southern Maryland; Paleocene (Teurian), Waipawa Section, New Zealand.
Occurrence in Present Study. Lower Paleocene, lower Ellenton Formation of Savannah River Site and surrounding area, South Carolina.
Holotype: Lucas-Clark, pl.2, figs.10–12.
Age: Paleocene.
Original description (Lucas-Clark, 2006)
Holotype. Plate 2, figs. 10–12. South Carolina, Savannah River Site, core C-10,211.3–210.0m, sample 9202.224, slide cg no. 2 of 2, CGS Zeiss Sh., coordinates 100.1 × 16.1, England Finder reference Q37/3. Carnegie Museum of Natural History CM 19151.
Derivation of name. After the Paleocene; no species of Phthanoperidinium have hitherto been described from the Paleocene.
Diagnosis. Highly variable, small to medium, pale peridinioid with tabulation variously expressed by low ridges, lineations, or lines of beads along sutures. Circular to ovoidal to rectangular/peridinioid in shape. Sometimes with scattered granules. Archeopyle 2a, always with accessory sutures on either side of 4″. Distinguished by variable expression of tabulation and archeopyle with accessory sutures.
Description. Small to medium, proximate, peridiniacean, cornucavate cysts, slightly dorsoventrally compressed, with a short apical horn and two unequally developed, short antapical horns. Right antapical horn shorter and less well developed than the left. Endophragm smooth, thicker than periphragm, appressed to periphragm except beneath horns and some sutural ridges. Endocyst circular to ovoidal to slightly peridinioid in outline, often with flat antapical margin; Pericyst peridinioid in shape with slightly angular outline due to sutural ridges or rounded peridinioid, or nearly circular. Lateral margins angular to smoothly convex; antapical margin curved concave to nearly flat. Periphragm thin, ornamented with low sutural ridges, or alternatively with sutures outlined by granules, ‘beads’ that may be small and faint or larger (verrucate), or by some combination of ridges and ‘beads’. Periphragm otherwise smooth or ornamented with a few or many pustules or granules which may be partly penitabular or random. Nearly complete tabulation expressed by ridges or beads along sutures; some sulcal sutures suppressed. Tabulation formula 4′, 3a, 7″, 5c, 5′″, 1as, 1ps, 2″″. First apical plate (1′) broadly spatulate and indented on the posterior edge where it is in contact with a camerate or arched anterior sulcal plate (as). Ornament on the first apical plate sometimes suggests a plate division at the camerate peak of the anterior sulcal plate. Archeopyle intercalary, type I/I (2a) or occasionally I+P by the loss of both 2a and 4″; accessory archeopyle sutures usually present on 3″/4″ and 4″/5″ sutures. Plate 2a operculum free, iso- to eurydeltaform. One archeopyle appears to penetrate both wall layers. Cingulum indicated by transverse parallel ridges that are sometimes surmounted with beads, and by local concavity; subdivided in some specimens into at least 5 plates by sutural ridges. Sulcus expressed by a depression in the ventral hypocyst and outlined by ridges so that the partial tabulation (anterior sulcal and posterior sulcal) can be interpreted, although individual sutures within the sulcal region are suppressed.
Dimensions. Length, 55–65 μm; width, 35–45 μm (10 specimens measured).
Remarks. In this species, the anterior sulcal plate is apparently camerate as if in contact with two, rather than one apical plate (1′). In some cases a suggestion of a partial suture dividing the first apical plate is present. However, such a departure from the usual peridinioid tabulation pattern is so unusual and seemingly unlikely that it is interpreted as an unusual shape for both the anterior sulcal and the first apical plates. The high degree of morphological variability, especially in terms of the expression of the tabulation (outline by ridges, large beads, small beads or combination) provides possibilities of attempting to subdivide this species, possibly into two or more subspecies. However, the end members often occur in the same sample, and no stratigraphic or biogeo-graphic evidence supports the designation of another species, or of subspecies. The holotype and paratype represent the most common morphological variants of this species. Other specimens illustrated represent less common, but persistent forms.
Comparison. Phthanoperidinium paleocenicum sp.nov. differs from most other species of this genus in having a more clear lyperidinioid shape with definite antapical horns. Of species reportedly with 2 antapical horns, it lacks the gonal spines of Phthanoperidinium alectrolophum, the sutural spines of Phthanoperidinium echinatum, the high sutural crests of Phthanoperidinium levimurum, and the hairs and branched appendages of Phthanoperidinium comatum. Phthanoperidinium paleocenicum sp. nov. resembles Phthanoperidinium brooksii, but apparently lacks the cancellous filling between walls, has more prominent antapical horns, is less ovoidal in shape, and does not vary in archeopyle type to encompass 3 intercalaries and/or 3 precingulars. Phthanoperidinium paleocenicum sp. nov. bears a strong general resemblance to Phthanoperidinium? eocenicum and its possible junior synonym Phthanoperidinium resisente, but clearly has two antapical horns rather than one or none, and has accessory archeopyle sutures around plate 4″.
Previously Reported Occurrence. Paleocene, Lower Bridge Member of the Williamsburg Formation (NP3, 4, or 5), Black Mingo Group of Berkeley County, South Carolina; Paleocene (Danian), Brightseat Formation of southern Maryland; Paleocene (Teurian), Waipawa Section, New Zealand.
Occurrence in Present Study. Lower Paleocene, lower Ellenton Formation of Savannah River Site and surrounding area, South Carolina.