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Angiosperm-like Pollen and Afropollis From the Middle Triassic (Anisian) of the Germanic Basin (Northern Switzerland)

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Angiosperm-like Pollen and Afropollis From the Middle Triassic (Anisian) of the Germanic Basin (Northern Switzerland)

Peter A Hochuli et al. Front Plant Sci.

Abstract

Here we report on angiosperm-like pollen and Afropollis from the Anisian (Middle Triassic, 247.2-242.0 Ma) of a mid-latitudinal site in Northern Switzerland. Small monosulcate pollen grains with typical reticulate (semitectate) sculpture, columellate structure of the sexine and thin nexine show close similarities to early angiosperm pollen known from the Early Cretaceous. However, they differ in their extremely thin inner layer (nexine). Six different pollen types (I-VI) are differentiated based on size, reticulation pattern, and exine structure. The described pollen grains show all the essential features of angiosperm pollen. However, considering the lack of a continuous record throughout the lower part of the Mesozoic and the comparison with the oldest Cretaceous finds we suggest an affinity to an angiosperm stem group. Together with the previously published records from the Middle Triassic of the Barents Sea area the angiosperm-like pollen grains reflect a considerable diversity of the parent plants during the Middle Triassic. Sedimentological evidence and associated palynofloras also suggest a remarkable ecological range for these plants. Associated with these grains we found pollen comparable to the genus Afropollis. Representatives of this genus are commonly recorded in Lower Cretaceous sediments of low latitudes, but until now had no record from the lower part of the Mesozoic.

Keywords: Afropollis; Middle Triassic; angiosperm stem group; angiosperm-like pollen; confocal laser scanning microscopy.

Figures

Figure 1
Figure 1
Location of the Weiach and Leuggern core holes.
Figure 2
Figure 2
Lithostratigraphic column of the Middle Triassic section of the Weiach core hole. 1, position of Afropollis; 2, range of angiosperm-like pollen grains.
Plate I
Plate I
Scale bars: 10 μm. (1), Pollen Type I, specimen A, LM image (high focus); (2), Pollen Type I, specimen A, CLSM image, total stack image/projection, anaglyph; (3), Pollen Type I, specimen A, CLSM partial stack image, proximal side; (4), Pollen Type I, specimen B, LM image (median focus); (5), Pollen Type I, specimen A, CLSM partial stack image, distal side; (6), Pollen Type I, specimen A, CLSM single image, optical section; (7), Pollen Type I, specimen B, CLSM total stack image/projection, anaglyph; (8), Pollen Type I, specimen B, CLSM partial stack image, lateral view (high focus); (9), Pollen Type I, specimen B, CLSM partial stack image, lateral view (low focus); (10), Pollen Type II, specimen A, LM image, high focus; (11), Pollen Type II, specimen A, LM image, low focus; (12), Pollen Type II, specimen A, CLSM total stack image/projection, anaglyph; (13), Pollen Type II, specimen A, CLSM partial stack image, lateral view on distal side (high focus); (14), Pollen Type II, specimen A, CLSM partial stack image, lateral view on proximal side (low focus); (15), Pollen Type II, specimen B, LM image, high focus; (16), Pollen Type II, specimen B, CLSM total stack image/projection.
Plate II
Plate II
Scale bars: 10 μm. (1), Pollen Type III, specimen A, LM image, median focus; (2), Pollen Type III, specimen A, LM image, (high focus); (3), Pollen Type III, specimen A, CLSM total stack image/projection, anaglyph; (4), Pollen Type III, specimen A, CLSM partial stack image, distal side (low focus); (5), Pollen Type III, specimen A, CLSM partial stack image, proximal side (high focus); (6), Pollen Type III, specimen B, LM image (high focus); (7), Pollen Type III, specimen B, LM image (low focus); (8), Pollen Type IV, specimen A, LM image (high focus); (9), Pollen Type III, specimen B, CLSM partial stack image, distal side (low focus); (10) Pollen Type III, specimen B, CLSM total stack image/projection, anaglyph; (11), Pollen Type IV, specimen A, CLSM total stack image/projection; (12), Pollen Type IV, specimen A, CLSM total stack image/projection, anaglyph; (13), Pollen Type IV, specimen B, LM image (median focus); (14) Pollen Type IV, specimen B, CLSM total stack image/projection, anaglyph; (15) Pollen Type IV, specimen B, CLSM total stack image/projection; (16) Pollen Type IV, specimen B, CLSM partial stack image, distal side (median focus).
Plate III
Plate III
Scale bars: 10 μm. (1), Pollen Type V, specimen A, LM image (median focus); (2), Pollen Type V, specimen A, LM image (high focus); (3) Pollen Type V, specimen A, CLSM total stack image/projection, anaglyph; (4) Pollen Type V, specimen A, CLSM partial stack image, distal side (high focus); (5) Pollen Type V, specimen A, CLSM partial stack image, proximal side (low focus); (6) Pollen Type V, specimen B, LM image (high focus); (7) Pollen Type V, specimen B, CLSM total stack image/projection; (8) Pollen Type V, specimen B, CLSM partial stack image, lateral view on distal side (low focus); (9) Pollen Type V, specimen B, CLSM total stack image/projection, anaglyph; (10) Pollen Type V, specimen C, CLSM total stack image/projection, anaglyph, lateral view; (11), Pollen Type V, specimen B, CLSM single image, optical section; (12), Pollen Type V, specimen C, CLSM total stack image/projection, lateral view; (13), Pollen Type V, specimen C, LM image, lateral view (high focus).
Plate IV
Plate IV
Scale bars: 10 μm, except (8) and (15) (20 μm); (1) Pollen Type VI, LM image (high focus); (2) Pollen Type VI, CLSM total stack image/projection, anaglyph; (3), Pollen Type VI, CLSM total stack image/projection; (4), Pollen Type VI, CLSM single image, optical section; (5), Afropollis sp. I, LM image (median focus); (6) Afropollis sp. I, CLSM total stack image/projection, anaglyph; (7) Eucommiidites sp. 1, CLSM total stack image/projection, anaglyph; (8), Eucommiidites sp. 1, LM image (median focus); (9) Afropollis sp. II, LM image, high focus; (10), Afropollis sp. II, CLSM total stack image/projection, anaglyph; (11), Eucommiidites sp. 1, CLSM single image, optical section; (12), Eucommiidites sp. 2, CLSM total stack image/projection, anaglyph; (13), Afropollis sp. II, CLSM total stack image/projection; (14), Eucommiidites sp. 2, CLSM single image, optical section; (15), Eucommiidites sp. 2, LM image (median focus).

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