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Apteodinium trifollicum
2016 Apteodinium ‘trifolliculum’; Browne et al. 2016
Description: A cyst of intermediate size, proximate, not dorso-ventrally compressed, pentagonal, with 1 apical and 1 antapical horn; episome slightly longer than hyposome. Apical horn variably developed up to c. 5 μm, apex rounded to subconical, episome more or less straight-sided; antapical horn weakly developed, round to acuminate. Cyst wall three-layered, comprising endophragm and periphragm, plus a variably developed ectophragm; cornucavate to bicavate, lateral pericoels absent. Endophragm thick (c. 2 μm); periphragm and ectophragm very thin. Archeopyle precingular, type P (3’’); large, operculum free. Processes lacking; surface ornament present, sutural, comprising poorly developed ridges/rugulae. Tabulation weakly expressed; formula indeterminate. Cingulum variably expressed, but usually distinct; indicated by sutural septa and depression of the cyst wall, commonly visible in the cyst outline.
Dimensions: Length = 50 (78) 107.5 μm (71 measurements); width = 46 (62) 81.2 μm (69 measurements).
Holotype: Figures A1. A–B, slide L27456/1, England Finder coordinates B32/1-2, specimen measures 84 × 69 μm.
Paratype: Figure A1.C, slide L27456/1, England Finder coordinates S27/4, specimen measures 84 × 62 μm.
Repository: National Paleontological Collection, GNS Science, Lower Hutt, New Zealand.
Type locality and strata: Waipawa Formation, Triangle Farm section in northern Wairarapa, New Zealand; New Zealand Map Grid coordinates 2767004 6029059 (Bland et al. 2014). Sample is registered as T26/f0533 in the New Zealand Fossil Record File (Clowes et al. 2021).
Stratigraphic occurrence: late early Paleocene (early Teurian) to early late Paleocene (late Teurian). While there are sparse poorly dated occurrences that may be possibly be older, the confirmed range of Apteodinium trifolliculum sp. nov. is from Zone NZDP5 to Zone NZDP7.
Etymology: Latin, folliculus: bag or shell, with reference to the three wall layers.
Comparison: This form appears to be an undescribed species of Apteodinium; the appearance of an ectophragm creating a third wall layer is a highly distinctive feature. The present taxon differs from other known species of Apteodinium in possessing an ectophragm (albeit incomplete) in addition to an endophragm and periphragm.
Apteodinium cornutum Cookson & Eisenack 1974 also occurs in the Paleocene but further differs in possessing a distinctive long, attenuated apical horn. Apteodinium fallax (Morgenroth 1968) Stover & Evitt 1978 is another Paleocene species which looks somewhat similar, but it has a much more strongly ornamented surface. Additionally, both Apteodinium cornutum and Apteodinium fallax have gently rounded outlines, whereas that of Apteodinum trifolliculum is slightly angular, especially at the cingulum.
Description: A cyst of intermediate size, proximate, not dorso-ventrally compressed, pentagonal, with 1 apical and 1 antapical horn; episome slightly longer than hyposome. Apical horn variably developed up to c. 5 μm, apex rounded to subconical, episome more or less straight-sided; antapical horn weakly developed, round to acuminate. Cyst wall three-layered, comprising endophragm and periphragm, plus a variably developed ectophragm; cornucavate to bicavate, lateral pericoels absent. Endophragm thick (c. 2 μm); periphragm and ectophragm very thin. Archeopyle precingular, type P (3’’); large, operculum free. Processes lacking; surface ornament present, sutural, comprising poorly developed ridges/rugulae. Tabulation weakly expressed; formula indeterminate. Cingulum variably expressed, but usually distinct; indicated by sutural septa and depression of the cyst wall, commonly visible in the cyst outline.
Dimensions: Length = 50 (78) 107.5 μm (71 measurements); width = 46 (62) 81.2 μm (69 measurements).
Holotype: Figures A1. A–B, slide L27456/1, England Finder coordinates B32/1-2, specimen measures 84 × 69 μm.
Paratype: Figure A1.C, slide L27456/1, England Finder coordinates S27/4, specimen measures 84 × 62 μm.
Repository: National Paleontological Collection, GNS Science, Lower Hutt, New Zealand.
Type locality and strata: Waipawa Formation, Triangle Farm section in northern Wairarapa, New Zealand; New Zealand Map Grid coordinates 2767004 6029059 (Bland et al. 2014). Sample is registered as T26/f0533 in the New Zealand Fossil Record File (Clowes et al. 2021).
Stratigraphic occurrence: late early Paleocene (early Teurian) to early late Paleocene (late Teurian). While there are sparse poorly dated occurrences that may be possibly be older, the confirmed range of Apteodinium trifolliculum sp. nov. is from Zone NZDP5 to Zone NZDP7.
Etymology: Latin, folliculus: bag or shell, with reference to the three wall layers.
Comparison: This form appears to be an undescribed species of Apteodinium; the appearance of an ectophragm creating a third wall layer is a highly distinctive feature. The present taxon differs from other known species of Apteodinium in possessing an ectophragm (albeit incomplete) in addition to an endophragm and periphragm.
Apteodinium cornutum Cookson & Eisenack 1974 also occurs in the Paleocene but further differs in possessing a distinctive long, attenuated apical horn. Apteodinium fallax (Morgenroth 1968) Stover & Evitt 1978 is another Paleocene species which looks somewhat similar, but it has a much more strongly ornamented surface. Additionally, both Apteodinium cornutum and Apteodinium fallax have gently rounded outlines, whereas that of Apteodinum trifolliculum is slightly angular, especially at the cingulum.