Back
Impagidinium elongatum
Impagidinium elongatum Schreck et al., 2012, p.89–90, pl.2, figs.6–20; text-figs.6–7.
Holotype: Schreck et al., 2012, pl.2, figs.6–10.
Age: Langhian–early Tortonian.
Original description (Schreck et al., 2012):
Impagidinium elongatum sp. nov. (Plate II, 6–20; Figs. 6, 7)
Synonyms:
1989 Impagidinium sp. 3; Manum et al., pl. 12, figs 2–4.
? 1989 Impagidinium sp. 1; Manum et al., pl. 17, figs 7, 8.
? 1992 Impagidinium sp. 1; Anstey, text-fig. 8, pl. 5, fig. 1–3; pl. 18, fig. 1.
? 1992 Impagidinium sp. 2; Anstey, text-fig. 9, pl. 5, fig. 4–6; pl. 18, fig. 2.
2002 Impagidinium sp. 1; Louwye, fig. 5 (9, 10).
Holotype: Sample 907A-13H-6, 20–22 cm; slide 2; England Finder reference P52/2; Plate II, 6–10.
Repository: Invertebrate Section of the Department of Palaeobiology, Royal Ontario Museum, Toronto, Ontario; catalog number ROM 61826.
Type locality: ODP Site 907, eastern Iceland Plateau (69°14.989′ N, 12°41.894′ W).
Stratigraphic horizon: ODP Hole 907A, 119.50 mbsf; lower Tortonian (lower Upper Miocene), Subchron C5n.2n, calibrated age 10.4 Ma. Etymology: Late Latin elongare, elongate, with reference to the characteristic shape of the central body of this species.
Diagnosis: A mid-sized to large species of Impagidinium of variable morphology with strongly elongated central body bearing low crests, some elevated at intersections. The surface is granulate, to granulopunctate, to nearly smooth. Plate 6″ is strongly triangular, owing to a steeply descending plate 6c, and narrowly contacts plate 1′+ 4′. Sulcal plates are usually weakly and incompletely expressed. Individual cingular plates are usually clearly demarcated, and the cingulum narrows towards boundaries between adjacent cingular plates. The development of sutural crests can be strongly reduced, especially in the equatorial and ventral areas.
Description: Proximate to proximochorate cysts with ovoidal to ovoidal–ellipsoidal central body having a length vs. equatorial diameter usually between 1.5 and 2.3 (a single exception registering 1.2). The central body wall is moderately thick (c. 0.6–1.3 μm) and the outer wall varies from distinctly granulate, to granulo-punctate, to nearly smooth, with thicker-walled specimens usually having more pronounced ornament. A low (up to 2.0 μm) apical protuberance may be present (Plate II, 13). Wall stratification is indistinguishable over most of the central body under LM. Low sutural crests demarcate with variable completeness a gonyaulacacean tabulation with neutral torsion, as for the genus. Crests are developed from the outer layer of the central body wall, and usually arise steeply from the central body surface, the two layers being closely appressed distally and for most or all of the height of the crests. However, slight cavation is occasionally developed at the base of crests, particularly where they intersect. Surface of crests varies from distinctly granulate, to granulo-punctate, to nearly smooth, as for the central body; and crests occasionally have small (up to 2–3 μm) perforations, or may even be fenestrate (Plate II, 18). Distal margins of crests may be straight, smoothly undulating, to irregular and occasionally serrated, with several types of margin often present on the same cyst. Crests may be mostly of even height, but all specimens have some crests raised at intersections, particularly between adjacent precingular and postcingular plates. Crests may be lower in mid-ventral and mid-dorsal areas. Crests usually demarcate the tabulation quite fully except within the sulcus, where plates are weakly and incompletely expressed by narrow lineations. In the apical area, the boundary between 1′ and 4′ is usually not expressed (Fig. 6), but rarely indicated by a faint and discontinuous line. The precingular and postcingular plates are mostly elongate. Plates 3″ and *4‴ are both mid-dorsally centered (Fig. 6) indicating neutral torsion. Plate 6″ is strongly triangular, owing to a steeply descending plate 6c, and narrowly contacts plate 1′+ 4′. Plate *1‴ is very narrow and located inside the sulcus, and is seldom expressed (Plate II, 16, 17). The sulcus is only slightly sigmoidal and is bordered by a non-overhanging cingulum, although the strongly triangular 6″ conforms to an S-type ventral organization (Fig. 6). The anterior margin of the posterior sulcal plate (ps) is usually expressed by a faint line, and the right sulcal plate may be also. The cingulum is laevorotatory and descends steeply where it approaches the sulcus from the right (plate 6c), resulting in an offset of about two widths. Both upper and lower margins of the cingulum are usually expressed on the ventral surface. Individual cingular plates are usually well demarcated, and the cingulum characteristically narrows towards boundaries between adjacent cingular plates, this being particularly evident on the dorsal surface. The archeopyle is reduced and elongated, and formed by loss of the third precingular plate.
Discussion: While the elongate central body, the tabulation, and low crests that in places slightly rise gonally are stable features, the morphology in general is very variable, and is probably a response to environmental change. In particular, specimens at the top of its range in Hole 907A, in Sample 13H-2, 142–144 cm, have extremely reduced crests in the equatorial region so that almost no tabulation can be discerned in this region (Plate II, 19–20). Samples 21H-6, 2–4 cm, 22H-2, 147–149 cm, and 22H-6, 51–53 cm, at the bottom of this species' range, also contain specimens with reduced crests. We interpret this feature as a response to unfavorable conditions, probably reduced salinity judging from other septate species (e.g. the cysts of Gonyaulax baltica; Ellegaard et al., 2002). A specimen illustrated by Manum et al. (1989, pl. 12, figs 2–4, as Impagidinium sp. 3) is intermediate between morphotypes with extremely reduced equatorial tabulation and those with normally expressed tabulation. A change in the dominant morphotype occurs at around 132 mbsf (11.24 Ma), with specimens in sample 15H-1, 74–76 cm and above being on average larger, with thicker central body walls, and with more strongly ornamented surfaces (e.g. Plate II, 6–10). This morphotype ranges down to sample 16H-1, 17–19 cm. Specimens in sample 15H-2, 38–40 cm (e.g. Plate II, 11–16) and below tend to be smaller, with thinner central body walls and faintly granulate to almost smooth surfaces (see Dimensions, and Fig. 7). However, there is intergradation as well as stratigraphic overlap between these morphologies, and we therefore treat them as a single species.
Dimensions: Holotype: central body length, 56 μm, central body width, 33 μm, maximum crest height, 4.5 μm, wall thickness, c. 1.0 μm. Range for specimens from samples 21H-6, 2–4 cm to 15H-2, 38–40 cm: central body length 39(47.7)59 μm, central body width 26(29.5)34 μm, central body length/width ratio 1.2(1.62)2.2, maximum crest height 1.5(4.1)7.0 μm, wall thickness c. 0.6(0.8)1.2 μm; 18 specimens measured. Range for specimens from samples 15H-1, 74–76 cm to 13H-2, 142–144 cm: central body length 52(56.0) 62 μm, central body width 23(30.9)37 μm, central body length/ width ratio 1.5(1.83)2.3, maximum crest height 3.8(4.7)5.5 μm, wall thickness c. 0.8(1.0)1.3 μm; 14 specimens measured. Overall range: central body length 39(51.3)62 μm, central body width 23(30.1) 37 μm, central body length/width ratio 1.2(1.71)2.3, maximum crest height 1.5(4.3)7 μm, wall thickness c. 0.6(0.9)1.3 μm; 32 specimens measured (see also Fig. 7).
Stratigraphic occurrence: In Hole 907A, Impagidinium elongatum ranges from the Langhian (14.1 Ma) through lower Tortonian (10.2 Ma); with occurrences below 12.6 Ma being sporadic, and an isolated specimen at 9.2 Ma considered reworked. Elsewhere recorded as Impagidinium sp. 3 in Manum et al. (1989) from the Lower through Upper Miocene of Norwegian Sea ODP Hole 643A (Manum et al., 1989; Bleil, 1989) and Middle Miocene of Norwegian Sea ODP Hole 642C (Manum et al., 1989; Bleil, 1989). Also recorded from the lower Tortonian Deurne Sands of Belgium (as Impagidinium sp. 1 in Louwye, 2002). Impagidinium sp. 1 of Manum et al. (1989) from the Upper Oligocene through upper Middle Miocene of Norwegian Sea ODP Hole 643A (Manum et al., 1989; Goll in Williams and Manum, 1999) and Lower Miocene of Norwegian Sea ODP Hole 642D (Manum et al., 1989; Bleil, 1989), is questionably synonymized with Impagidinium elongatum. Impagidinium sp. 1 and 2 of Anstey (1992) from the late Middle? to early Late Miocene of Baffin Bay ODP Hole 645E are probably conspecific with I. elongatum.
Holotype: Schreck et al., 2012, pl.2, figs.6–10.
Age: Langhian–early Tortonian.
Original description (Schreck et al., 2012):
Impagidinium elongatum sp. nov. (Plate II, 6–20; Figs. 6, 7)
Synonyms:
1989 Impagidinium sp. 3; Manum et al., pl. 12, figs 2–4.
? 1989 Impagidinium sp. 1; Manum et al., pl. 17, figs 7, 8.
? 1992 Impagidinium sp. 1; Anstey, text-fig. 8, pl. 5, fig. 1–3; pl. 18, fig. 1.
? 1992 Impagidinium sp. 2; Anstey, text-fig. 9, pl. 5, fig. 4–6; pl. 18, fig. 2.
2002 Impagidinium sp. 1; Louwye, fig. 5 (9, 10).
Holotype: Sample 907A-13H-6, 20–22 cm; slide 2; England Finder reference P52/2; Plate II, 6–10.
Repository: Invertebrate Section of the Department of Palaeobiology, Royal Ontario Museum, Toronto, Ontario; catalog number ROM 61826.
Type locality: ODP Site 907, eastern Iceland Plateau (69°14.989′ N, 12°41.894′ W).
Stratigraphic horizon: ODP Hole 907A, 119.50 mbsf; lower Tortonian (lower Upper Miocene), Subchron C5n.2n, calibrated age 10.4 Ma. Etymology: Late Latin elongare, elongate, with reference to the characteristic shape of the central body of this species.
Diagnosis: A mid-sized to large species of Impagidinium of variable morphology with strongly elongated central body bearing low crests, some elevated at intersections. The surface is granulate, to granulopunctate, to nearly smooth. Plate 6″ is strongly triangular, owing to a steeply descending plate 6c, and narrowly contacts plate 1′+ 4′. Sulcal plates are usually weakly and incompletely expressed. Individual cingular plates are usually clearly demarcated, and the cingulum narrows towards boundaries between adjacent cingular plates. The development of sutural crests can be strongly reduced, especially in the equatorial and ventral areas.
Description: Proximate to proximochorate cysts with ovoidal to ovoidal–ellipsoidal central body having a length vs. equatorial diameter usually between 1.5 and 2.3 (a single exception registering 1.2). The central body wall is moderately thick (c. 0.6–1.3 μm) and the outer wall varies from distinctly granulate, to granulo-punctate, to nearly smooth, with thicker-walled specimens usually having more pronounced ornament. A low (up to 2.0 μm) apical protuberance may be present (Plate II, 13). Wall stratification is indistinguishable over most of the central body under LM. Low sutural crests demarcate with variable completeness a gonyaulacacean tabulation with neutral torsion, as for the genus. Crests are developed from the outer layer of the central body wall, and usually arise steeply from the central body surface, the two layers being closely appressed distally and for most or all of the height of the crests. However, slight cavation is occasionally developed at the base of crests, particularly where they intersect. Surface of crests varies from distinctly granulate, to granulo-punctate, to nearly smooth, as for the central body; and crests occasionally have small (up to 2–3 μm) perforations, or may even be fenestrate (Plate II, 18). Distal margins of crests may be straight, smoothly undulating, to irregular and occasionally serrated, with several types of margin often present on the same cyst. Crests may be mostly of even height, but all specimens have some crests raised at intersections, particularly between adjacent precingular and postcingular plates. Crests may be lower in mid-ventral and mid-dorsal areas. Crests usually demarcate the tabulation quite fully except within the sulcus, where plates are weakly and incompletely expressed by narrow lineations. In the apical area, the boundary between 1′ and 4′ is usually not expressed (Fig. 6), but rarely indicated by a faint and discontinuous line. The precingular and postcingular plates are mostly elongate. Plates 3″ and *4‴ are both mid-dorsally centered (Fig. 6) indicating neutral torsion. Plate 6″ is strongly triangular, owing to a steeply descending plate 6c, and narrowly contacts plate 1′+ 4′. Plate *1‴ is very narrow and located inside the sulcus, and is seldom expressed (Plate II, 16, 17). The sulcus is only slightly sigmoidal and is bordered by a non-overhanging cingulum, although the strongly triangular 6″ conforms to an S-type ventral organization (Fig. 6). The anterior margin of the posterior sulcal plate (ps) is usually expressed by a faint line, and the right sulcal plate may be also. The cingulum is laevorotatory and descends steeply where it approaches the sulcus from the right (plate 6c), resulting in an offset of about two widths. Both upper and lower margins of the cingulum are usually expressed on the ventral surface. Individual cingular plates are usually well demarcated, and the cingulum characteristically narrows towards boundaries between adjacent cingular plates, this being particularly evident on the dorsal surface. The archeopyle is reduced and elongated, and formed by loss of the third precingular plate.
Discussion: While the elongate central body, the tabulation, and low crests that in places slightly rise gonally are stable features, the morphology in general is very variable, and is probably a response to environmental change. In particular, specimens at the top of its range in Hole 907A, in Sample 13H-2, 142–144 cm, have extremely reduced crests in the equatorial region so that almost no tabulation can be discerned in this region (Plate II, 19–20). Samples 21H-6, 2–4 cm, 22H-2, 147–149 cm, and 22H-6, 51–53 cm, at the bottom of this species' range, also contain specimens with reduced crests. We interpret this feature as a response to unfavorable conditions, probably reduced salinity judging from other septate species (e.g. the cysts of Gonyaulax baltica; Ellegaard et al., 2002). A specimen illustrated by Manum et al. (1989, pl. 12, figs 2–4, as Impagidinium sp. 3) is intermediate between morphotypes with extremely reduced equatorial tabulation and those with normally expressed tabulation. A change in the dominant morphotype occurs at around 132 mbsf (11.24 Ma), with specimens in sample 15H-1, 74–76 cm and above being on average larger, with thicker central body walls, and with more strongly ornamented surfaces (e.g. Plate II, 6–10). This morphotype ranges down to sample 16H-1, 17–19 cm. Specimens in sample 15H-2, 38–40 cm (e.g. Plate II, 11–16) and below tend to be smaller, with thinner central body walls and faintly granulate to almost smooth surfaces (see Dimensions, and Fig. 7). However, there is intergradation as well as stratigraphic overlap between these morphologies, and we therefore treat them as a single species.
Dimensions: Holotype: central body length, 56 μm, central body width, 33 μm, maximum crest height, 4.5 μm, wall thickness, c. 1.0 μm. Range for specimens from samples 21H-6, 2–4 cm to 15H-2, 38–40 cm: central body length 39(47.7)59 μm, central body width 26(29.5)34 μm, central body length/width ratio 1.2(1.62)2.2, maximum crest height 1.5(4.1)7.0 μm, wall thickness c. 0.6(0.8)1.2 μm; 18 specimens measured. Range for specimens from samples 15H-1, 74–76 cm to 13H-2, 142–144 cm: central body length 52(56.0) 62 μm, central body width 23(30.9)37 μm, central body length/ width ratio 1.5(1.83)2.3, maximum crest height 3.8(4.7)5.5 μm, wall thickness c. 0.8(1.0)1.3 μm; 14 specimens measured. Overall range: central body length 39(51.3)62 μm, central body width 23(30.1) 37 μm, central body length/width ratio 1.2(1.71)2.3, maximum crest height 1.5(4.3)7 μm, wall thickness c. 0.6(0.9)1.3 μm; 32 specimens measured (see also Fig. 7).
Stratigraphic occurrence: In Hole 907A, Impagidinium elongatum ranges from the Langhian (14.1 Ma) through lower Tortonian (10.2 Ma); with occurrences below 12.6 Ma being sporadic, and an isolated specimen at 9.2 Ma considered reworked. Elsewhere recorded as Impagidinium sp. 3 in Manum et al. (1989) from the Lower through Upper Miocene of Norwegian Sea ODP Hole 643A (Manum et al., 1989; Bleil, 1989) and Middle Miocene of Norwegian Sea ODP Hole 642C (Manum et al., 1989; Bleil, 1989). Also recorded from the lower Tortonian Deurne Sands of Belgium (as Impagidinium sp. 1 in Louwye, 2002). Impagidinium sp. 1 of Manum et al. (1989) from the Upper Oligocene through upper Middle Miocene of Norwegian Sea ODP Hole 643A (Manum et al., 1989; Goll in Williams and Manum, 1999) and Lower Miocene of Norwegian Sea ODP Hole 642D (Manum et al., 1989; Bleil, 1989), is questionably synonymized with Impagidinium elongatum. Impagidinium sp. 1 and 2 of Anstey (1992) from the late Middle? to early Late Miocene of Baffin Bay ODP Hole 645E are probably conspecific with I. elongatum.