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Dapcodinium morganii
Dapcodinium morganii sp. nov., Mantle et al. 2020, p. 36-37
Holotype: Mantle et al. 2020, Plate VII, 19
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (Norian–Rhaetian)
Original description: Mantle et al. 2020:
Description:
Small, proximate, acavate, or cavate, spheroidal to ovoidal dinoflagellate cysts with rounded poles and approximately equant epicysts and hypocysts.
Wall: surface ornament varies from scabrate to granulate, with the grana commonly coalescing to form minute, longitudinal rugulae which impart a finely wrinkled appearance. The alignment of the grana, or very low ridges, indicate an incomplete tabulation
Tabulation: ?4′, 4+a, 7′′, nc, 6+′′′, n′′′′, ns.
The broad (3–6 μm) cingulum is largely undivided, with only rare hints of internal tabulation and typically is not indented.
Archaeopyle: compound, commonly only includes dorsal plates 3′, 4′, 3a, and 4a.
Remarks:
Although very similar to Dapcodinium ovale, the specimens recorded during this study exhibit minor but consistent differences to that taxon, and are notably older. Dapcodinium ovale occurs in the Lower and Middle Jurassic of the Northern Hemisphere. Below (1987) described Dapcodinium ovale from the Pliensbachian to Bajocian of Germany, Poland, and Spitsbergen. Further reports include those of questionable specimens by Prauss (1989) from the Toarcian to Aalenian of northwest Germany, and Smelror (1993) from the Toarcian to Bajocian of the Barents Sea region. Thus, the Norian–Rhaetian Australian specimens described herein are considered to represent a closely comparable, but biostratigraphically distinct, new species.
Dimensions:
Overall length (excluding the apical plates) 26 μm (31 μm) 35 μm; maximum width 24 μm (28 μm) 32 μm
20 measured specimens
Affinities/Comparison:
The incomplete tabulation of ?4′, 4+a, 7′′, nc, 6+′′′, n′′′′, ns observed for Dapcodinium morganii sp. nov. appears to be broadly consistent with that described by Below (1987) for Dapcodinium ovale, which was PR, 5′, 6a, 7′′, 8c, 7′′′, 3′′′′, as, y, z, ps. The combination, apical and anterior intercalary, archaeopyle is formed by the compound loss of plates. In Dapcodinium morganii sp. nov., this typically includes only the dorsal plates, i.e. 3′, 4′, 3a, and 4a (Fig. 5c), but this is not as unequivocally demonstrated as for the type material of Dapcodinium ovale (Below, 1987, pl. 24, figs. 1–15). Below (1987) also noted that a small number of specimens lost their PR, 2′, 1a, and 2a plates during excystment; the loss of these plates for Dapcodinium morganii sp. nov. has not been confirmed. Despite these similarities, there are consistent, albeit relatively minor, differences between Dapcodinium morganii and D. ovale. These include the marginally smaller size and greater variability in shape (i.e., spherical to ovoidal, rather than strictly ovoidal) of the former. The somewhat “hooded” appearance suggested by the frequent loss of only the mediodorsal 3′, 4′, 3a, and 4a plates is shared by both taxa, as is the longitudinal alignment of fine grana that commonly gives the cyst surface a very finely wrinkled appearance. Unfortunately, it is difficult to compare some morphological features between this new Australian species, that was studied with a transmitted light microscope, with the SEM images of the type material of Dapcodinium ovale (Below, 1987). Thus, it is not clear if the much thinner epicystal plates, a very characteristic trait of the Australian assemblages, is a feature shared by Dapcodinium ovale in the younger European and Arctic palynofloras. Furthermore, this new Australian species frequently exhibits some antapical cavation, and rarely circumcavation, that is not recorded for Dapcodinium ovale.
Holotype: Mantle et al. 2020, Plate VII, 19
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (Norian–Rhaetian)
Original description: Mantle et al. 2020:
Description:
Small, proximate, acavate, or cavate, spheroidal to ovoidal dinoflagellate cysts with rounded poles and approximately equant epicysts and hypocysts.
Wall: surface ornament varies from scabrate to granulate, with the grana commonly coalescing to form minute, longitudinal rugulae which impart a finely wrinkled appearance. The alignment of the grana, or very low ridges, indicate an incomplete tabulation
Tabulation: ?4′, 4+a, 7′′, nc, 6+′′′, n′′′′, ns.
The broad (3–6 μm) cingulum is largely undivided, with only rare hints of internal tabulation and typically is not indented.
Archaeopyle: compound, commonly only includes dorsal plates 3′, 4′, 3a, and 4a.
Remarks:
Although very similar to Dapcodinium ovale, the specimens recorded during this study exhibit minor but consistent differences to that taxon, and are notably older. Dapcodinium ovale occurs in the Lower and Middle Jurassic of the Northern Hemisphere. Below (1987) described Dapcodinium ovale from the Pliensbachian to Bajocian of Germany, Poland, and Spitsbergen. Further reports include those of questionable specimens by Prauss (1989) from the Toarcian to Aalenian of northwest Germany, and Smelror (1993) from the Toarcian to Bajocian of the Barents Sea region. Thus, the Norian–Rhaetian Australian specimens described herein are considered to represent a closely comparable, but biostratigraphically distinct, new species.
Dimensions:
Overall length (excluding the apical plates) 26 μm (31 μm) 35 μm; maximum width 24 μm (28 μm) 32 μm
20 measured specimens
Affinities/Comparison:
The incomplete tabulation of ?4′, 4+a, 7′′, nc, 6+′′′, n′′′′, ns observed for Dapcodinium morganii sp. nov. appears to be broadly consistent with that described by Below (1987) for Dapcodinium ovale, which was PR, 5′, 6a, 7′′, 8c, 7′′′, 3′′′′, as, y, z, ps. The combination, apical and anterior intercalary, archaeopyle is formed by the compound loss of plates. In Dapcodinium morganii sp. nov., this typically includes only the dorsal plates, i.e. 3′, 4′, 3a, and 4a (Fig. 5c), but this is not as unequivocally demonstrated as for the type material of Dapcodinium ovale (Below, 1987, pl. 24, figs. 1–15). Below (1987) also noted that a small number of specimens lost their PR, 2′, 1a, and 2a plates during excystment; the loss of these plates for Dapcodinium morganii sp. nov. has not been confirmed. Despite these similarities, there are consistent, albeit relatively minor, differences between Dapcodinium morganii and D. ovale. These include the marginally smaller size and greater variability in shape (i.e., spherical to ovoidal, rather than strictly ovoidal) of the former. The somewhat “hooded” appearance suggested by the frequent loss of only the mediodorsal 3′, 4′, 3a, and 4a plates is shared by both taxa, as is the longitudinal alignment of fine grana that commonly gives the cyst surface a very finely wrinkled appearance. Unfortunately, it is difficult to compare some morphological features between this new Australian species, that was studied with a transmitted light microscope, with the SEM images of the type material of Dapcodinium ovale (Below, 1987). Thus, it is not clear if the much thinner epicystal plates, a very characteristic trait of the Australian assemblages, is a feature shared by Dapcodinium ovale in the younger European and Arctic palynofloras. Furthermore, this new Australian species frequently exhibits some antapical cavation, and rarely circumcavation, that is not recorded for Dapcodinium ovale.