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Messelodinium thielepfeifferae
Messelodinium thielepfeifferae Lenz et al., 2007, p.124,126, pl.1, figs.1–16; pl.2, figs.1–3; pl.3, figs.1–3; pl.4, figs.1–6.
Holotype: Lenz et al., 2007, pl.1, figs.1–2.
Age: middle Eocene.
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Original description (Lenz et al., 2007)
Messelodinium thielepfeifferae sp. nov. Plate 1, figs. 1-16; Plate 2, figs. 1-3; Plate 3, figs. 1-3; Plate 4, figs. 1-6
Holotype. Plate 1, figs. 1,2. Slide 58-1, England Finder coordinate E44/0. Dimensions: length 37 µm; width 31 µm. Type locality: Messel pit, exploration well 'Messel 2001 ', depth 167.24 m. Type horizon: Lower Messel Formation, Middle Eocene. Repository: Paleobotany Section, Forschungsinstitut Senckenberg und Naturhistorisches Museum (Research Institute Senckenberg and Natural History Museum) Frankfurt am Main, Germany; collection number SM.B Me 6193/1-1.
Paratype. Plate 1, fig. 12. Slide 172-1, England Finder coordinate R43/0. Dimensions: length 37 µm; width 30 µm. Type locality: Messel pit, exploration well 'Messel 2001 ', depth 140.08 m. Type horizon: Lower Messel Formation, Middle Eocene. Repository: Paleobotany Section, Forschungsinstitut Senckenberg und Naturhistorisches Museum (Research Institute Senckenberg and Natural History Museum) Frankfurt am Main, Germany; collection number SM.B Me 6173/1-II.
Derivation of name. After Heidemarie Thiele-Pfeiffer, who carried out the first detailed palynological study of the Messel oil shale and identified and illustrated these dinoflagellate cysts as 'freshwater phytoplankton' (Thiele-Pfeiffer, 1988, pl. 16, figs. 45-47).
Diagnosis. As for genus. The wall in transmitted light is finely wrinkled or granular to nearly smooth; under SEM it is rugulate to granulate.
Description. Proximate, acavate peridinioid dinoflagellate cysts, with a subspherical to elongate ellipsoidal outline, but commonly folded into various shapes due to the thinness of the wall. Apex and antapex rounded, apex occasionally with a blunt apical peak (Plate 1, fig. 7), distinct apical and antapical horns lacking. The cyst wall is extremely thin (< 1 µm), single-layered, consisting of autophragm only (Plate 2, fig. 3 ; Plate 3, fig. 3). In transmitted light, the wall appears colorless and psilate (Plate 1, figs. 1,2) and faintly sculptured (Plate 1, fig. 12). Scanning electron micrographs show that the wall surface is never entirely smooth (Plate 4), but finely rugulate to loosely granulate. A regular paratabulation is not developed, but paratabulation can be inferred from the position of the archeopyle, paracingulum, and parasulcus. The archeopyle is of intercalary type I(2a) (Plate 2, fig. 1); the operculum appears to be mostly attached (Plate 3, fig. 1). The paracingulum and parasulcus are recognizable as shallow depressions only (Plate 1, figs. 13,16; Plate 2).
Dimensions. Length: maximum 42.0 µm, mean 36.1 µm, minimum 30.0 µm; width: maximum 38.4 µm, mean 30.4 µm, minimum 22.8 µm. Sixty-four specimens without significant folding were measured.
Remarks. Messelodinium thielepfeifferae gen. et sp. nov. is identical with the 'freshwater phytoplankton' figured by Thiele-Pfeiffer (1988, pi. 16, figs. 45-47). The cysts recognized as 'dinoflagellates' in translucent chips offish coprolites and background sediment from the Messel oil shale by Richter and Clausing (2004) and Richter and Wedmann (2005) are probably also conspecific. Messelodinium thielepfeifferae gen. et sp. nov. was previously designated as Geiselodinium sp. in Lenz et al. (2007) because of a superficial similarity to Geiselodinium Krutzsch 1962. However, the original diagnosis of Geiselodinium clearly states that this genus is cávate (Krutzsch, 1962). This is also indicated by line drawings of species of Geiselodinium, although the accompanying photomicrographs are not entirely conclusive (Krutzsch, 1962; Krutzsch and Pacltová, 1990). Subsequent restudies have consistently revealed that the dinoflagellate cysts from Messel are acavate, having a thin autophragm only. This is clearly confirmed by SEM micrographs of specimens with open archeopyles, showing a single wall layer only (Plate 2, figs. 1-3). Here, the thickness of the autophragm is shown to be less than 1 µm. Scanning electron micrographs also show that, in the majority of specimens, the surface is finely rugulate giving the wall a wrinkled appearance (Plate 3, figs. 1,2). Some specimens, however, only bear loosely spaced grana (< 0.5 µm) of low relief (e.g. Plate 3, fig. 3). Both types of ornamentation are closely associated with acmes of these dinoflagellate cysts (Plate 4, figs. 1,3). That this difference in wall ornamentation is due to intraspecific variation is confirmed by specimens with transitional sculpture (Plate 2, fig. 2), and by rare specimens having both granulate and rugulate ornamentation (Plate 4, figs. 2, 4). Obviously, specimens with a rugulate surface appear slightly ornamented even in transmitted light (e.g. Plate 1, figs. 7- 12), while those with a more granulate surface appear to be scabrate (e.g. Plate 1, figs. 1-6). The archeopyle cannot be identified with certainty in transmitted light due to the thinness of the cyst wall, and the lack of contrast. In SEM micrographs, however, several specimens showed an open archeopyle with a hexagonal outline (Plate 2, fig. 1 ). The intercalary position can usually be inferred from the trace of the paracingulum indicated by a slight depression, and minute changes in surface ornamentation. Examples of possible reconstructions of the archeopyle, paracingulum, and parasulcus are shown in Plates 2 and 3. A cyst in dorsal view presumably with the operculum still attached is shown in Plate 3, fig. 1. The archeopyle, paracingulum, and parasulcus are also assumed to characterize areas of failure of the cyst wall during compaction.
Comparison. Superficially, Messelodinium thielepfeifferae gen. et sp. nov. closely resembles the three species of Geiselodinium described by Krutzsch ( 1962) from the Middle Eocene lignite of the Geiseltal Valley, near Halle, Germany. Besides being cávate, the three species oí Geiselodinium are larger than Messelodinium thielepfeifferae gen. et sp. nov., and may be variants of a single species. Details of the surface ornamentation may offer additional characteristics to distinguish Messelodinium thielepfeifferae gen. et sp. nov. from other similar cysts of freshwater dinoflagellates. Pseudokomewuia aff. granulata He Chengquan 1980 of Batten et al. (1999) resembles the granular variety of Messelodinium thielepfeifferae gen. et sp. nov., but is cornucavate. Furthermore, the surface ornamentation in Pseudokomewuia aff. granulata He Chengquan 1980 of Batten et al. (1999) appears to be more prominent.
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Holotype: Lenz et al., 2007, pl.1, figs.1–2.
Age: middle Eocene.
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Original description (Lenz et al., 2007)
Messelodinium thielepfeifferae sp. nov. Plate 1, figs. 1-16; Plate 2, figs. 1-3; Plate 3, figs. 1-3; Plate 4, figs. 1-6
Holotype. Plate 1, figs. 1,2. Slide 58-1, England Finder coordinate E44/0. Dimensions: length 37 µm; width 31 µm. Type locality: Messel pit, exploration well 'Messel 2001 ', depth 167.24 m. Type horizon: Lower Messel Formation, Middle Eocene. Repository: Paleobotany Section, Forschungsinstitut Senckenberg und Naturhistorisches Museum (Research Institute Senckenberg and Natural History Museum) Frankfurt am Main, Germany; collection number SM.B Me 6193/1-1.
Paratype. Plate 1, fig. 12. Slide 172-1, England Finder coordinate R43/0. Dimensions: length 37 µm; width 30 µm. Type locality: Messel pit, exploration well 'Messel 2001 ', depth 140.08 m. Type horizon: Lower Messel Formation, Middle Eocene. Repository: Paleobotany Section, Forschungsinstitut Senckenberg und Naturhistorisches Museum (Research Institute Senckenberg and Natural History Museum) Frankfurt am Main, Germany; collection number SM.B Me 6173/1-II.
Derivation of name. After Heidemarie Thiele-Pfeiffer, who carried out the first detailed palynological study of the Messel oil shale and identified and illustrated these dinoflagellate cysts as 'freshwater phytoplankton' (Thiele-Pfeiffer, 1988, pl. 16, figs. 45-47).
Diagnosis. As for genus. The wall in transmitted light is finely wrinkled or granular to nearly smooth; under SEM it is rugulate to granulate.
Description. Proximate, acavate peridinioid dinoflagellate cysts, with a subspherical to elongate ellipsoidal outline, but commonly folded into various shapes due to the thinness of the wall. Apex and antapex rounded, apex occasionally with a blunt apical peak (Plate 1, fig. 7), distinct apical and antapical horns lacking. The cyst wall is extremely thin (< 1 µm), single-layered, consisting of autophragm only (Plate 2, fig. 3 ; Plate 3, fig. 3). In transmitted light, the wall appears colorless and psilate (Plate 1, figs. 1,2) and faintly sculptured (Plate 1, fig. 12). Scanning electron micrographs show that the wall surface is never entirely smooth (Plate 4), but finely rugulate to loosely granulate. A regular paratabulation is not developed, but paratabulation can be inferred from the position of the archeopyle, paracingulum, and parasulcus. The archeopyle is of intercalary type I(2a) (Plate 2, fig. 1); the operculum appears to be mostly attached (Plate 3, fig. 1). The paracingulum and parasulcus are recognizable as shallow depressions only (Plate 1, figs. 13,16; Plate 2).
Dimensions. Length: maximum 42.0 µm, mean 36.1 µm, minimum 30.0 µm; width: maximum 38.4 µm, mean 30.4 µm, minimum 22.8 µm. Sixty-four specimens without significant folding were measured.
Remarks. Messelodinium thielepfeifferae gen. et sp. nov. is identical with the 'freshwater phytoplankton' figured by Thiele-Pfeiffer (1988, pi. 16, figs. 45-47). The cysts recognized as 'dinoflagellates' in translucent chips offish coprolites and background sediment from the Messel oil shale by Richter and Clausing (2004) and Richter and Wedmann (2005) are probably also conspecific. Messelodinium thielepfeifferae gen. et sp. nov. was previously designated as Geiselodinium sp. in Lenz et al. (2007) because of a superficial similarity to Geiselodinium Krutzsch 1962. However, the original diagnosis of Geiselodinium clearly states that this genus is cávate (Krutzsch, 1962). This is also indicated by line drawings of species of Geiselodinium, although the accompanying photomicrographs are not entirely conclusive (Krutzsch, 1962; Krutzsch and Pacltová, 1990). Subsequent restudies have consistently revealed that the dinoflagellate cysts from Messel are acavate, having a thin autophragm only. This is clearly confirmed by SEM micrographs of specimens with open archeopyles, showing a single wall layer only (Plate 2, figs. 1-3). Here, the thickness of the autophragm is shown to be less than 1 µm. Scanning electron micrographs also show that, in the majority of specimens, the surface is finely rugulate giving the wall a wrinkled appearance (Plate 3, figs. 1,2). Some specimens, however, only bear loosely spaced grana (< 0.5 µm) of low relief (e.g. Plate 3, fig. 3). Both types of ornamentation are closely associated with acmes of these dinoflagellate cysts (Plate 4, figs. 1,3). That this difference in wall ornamentation is due to intraspecific variation is confirmed by specimens with transitional sculpture (Plate 2, fig. 2), and by rare specimens having both granulate and rugulate ornamentation (Plate 4, figs. 2, 4). Obviously, specimens with a rugulate surface appear slightly ornamented even in transmitted light (e.g. Plate 1, figs. 7- 12), while those with a more granulate surface appear to be scabrate (e.g. Plate 1, figs. 1-6). The archeopyle cannot be identified with certainty in transmitted light due to the thinness of the cyst wall, and the lack of contrast. In SEM micrographs, however, several specimens showed an open archeopyle with a hexagonal outline (Plate 2, fig. 1 ). The intercalary position can usually be inferred from the trace of the paracingulum indicated by a slight depression, and minute changes in surface ornamentation. Examples of possible reconstructions of the archeopyle, paracingulum, and parasulcus are shown in Plates 2 and 3. A cyst in dorsal view presumably with the operculum still attached is shown in Plate 3, fig. 1. The archeopyle, paracingulum, and parasulcus are also assumed to characterize areas of failure of the cyst wall during compaction.
Comparison. Superficially, Messelodinium thielepfeifferae gen. et sp. nov. closely resembles the three species of Geiselodinium described by Krutzsch ( 1962) from the Middle Eocene lignite of the Geiseltal Valley, near Halle, Germany. Besides being cávate, the three species oí Geiselodinium are larger than Messelodinium thielepfeifferae gen. et sp. nov., and may be variants of a single species. Details of the surface ornamentation may offer additional characteristics to distinguish Messelodinium thielepfeifferae gen. et sp. nov. from other similar cysts of freshwater dinoflagellates. Pseudokomewuia aff. granulata He Chengquan 1980 of Batten et al. (1999) resembles the granular variety of Messelodinium thielepfeifferae gen. et sp. nov., but is cornucavate. Furthermore, the surface ornamentation in Pseudokomewuia aff. granulata He Chengquan 1980 of Batten et al. (1999) appears to be more prominent.
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