Microdictyon sp.
publication ID |
https://doi.org/ 10.4202/app.2012.0004 |
persistent identifier |
https://treatment.plazi.org/id/03C3891D-1510-C24C-FCC9-FBDACEE3F9E2 |
treatment provided by |
Felipe |
scientific name |
Microdictyon sp. |
status |
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Fig. 56 View Fig .
Material.—Single fragments from samples 3/60 and 6/66.2; two, SMNH X 4782 and 4783, from sample 7/34.7 and six fragments from sample 7/39.5; Emyaksin Formation, Malaya Kuonamka and Bol’shaya Kuonamka rivers; correlated with the upper Delgadella anabara Zone (samples 7/34.7 and 7/39.5) and Judomia Zone, Atdabanian Stage.
Description.—Fragments of Microdictyon sclerites with partly preserved margin (margin in the lower part of the Fig. 56A View Fig 2 View Fig , A 3 View Fig , B 4 View Fig ). The fragments have distinct rounded, almost circular holes surrounded by 5–8 cap-like nodes.Additionally, smaller nodes are present along the margin of sclerite ( Fig. 56A View Fig 2 View Fig , A 3 View Fig ). The diameter of the holes increases from ca. 15 μm at the very margin of the sclerite to at least 70 μm centrally. The nodes have an initial diameter of ca. 10 μm at the margin of the sclerite, increasing up to at least 50 μm proximally. These nodes start at the margin as tubercles and progress into larger cones,>30 μm tall, with flared bases and tips shifted towards the centre of the sclerite. The holes are not closed from below.
Remarks.— Microdictyon sp. described herein is similar to Microdictyon rhomboidale , described above, but determination of its affinity is hampered by incomplete preservation. Chemostratigraphy ( Fig. 2 View Fig and Kouchinsky et al. 2001, 2012) indicates that Microdictyon sp. , from the upper Delgadella anabara Zone, Atdabanian Stage , is the earliest lobopodian
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fossil known from Siberia. This occurrence is correlated chemostratigraphically (Dilliard et al. 2007) with the regional first appearance of Microdictyon sp. and Microdictyon cf. M. rhomboidale in the lower Nevadella Zone of Laurentia (see above, Bengtson et al. 1986; Voronova et al. 1987) and, probably, with the first occurrence of M. sphaeroides Hinz, 1987 in the Camenella baltica Zone of Avalonia ( Hinz, 1987) and Microdictyon depressum Bengtson in Bengtson et al., 1990 in the Abadiella huoi Zone of Australia ( Topper et al. 2011; Kouchinsky et al. 2012).
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