Pomerantsoceras tibia, Kröger, 2007
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publication ID |
https://doi.org/ 10.5281/zenodo.13741383 |
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persistent identifier |
https://treatment.plazi.org/id/039187AC-7F39-6002-FCB0-FF61E21EF89E |
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treatment provided by |
Felipe |
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scientific name |
Pomerantsoceras tibia |
| status |
sp. nov. |
Pomerantsoceras tibia sp. nov.
Figs. 4D, E View Fig , 6A, C View Fig , 7G View Fig .
Derivation of the name: From Latin tibia , flute, referring to the longiconic shell.
Holotype: TUG 1227/14.
Type locality: Porkuni, north Estonia.
Type horizon: Siuge Member, Porkuni Regional Stage, Late Ordovician.
Material.— Eighteen specimens displaying embryonic, juvenile, adolescent and mature growth stages in collection of TUG .
Diagnosis.—Same as for genus, by monotypy.
Description.— Holotype TUG 1227/14 ( Fig. 7G View Fig ) is fragment of juvenile growth stages with nearly complete body chamber and total length of 16 mm. Maximum dorso−ventral diameter is 4.7 mm, maximum lateral diameter 3.8 mm, minimum dorso−ventral diameter 2.9 mm, minimum lateral diameter 2.6 mm. Shell surface is smooth. Conch is slightly cyrtocone. Body chamber length is 7.8 mm. Last septum is at dorso−ventral diameter 3.8 mm, lateral diameter 3.2 mm. Distance between last septum and preceding septum is 0.8 mm. Siphuncle is marginal at convex side of growth axis with septal perforation of approximately 0.3 mm at last septum. Sutures form saddle at ventral side and lobe at flanks. Curvature of last chamber is 0.4 mm deep.
Specimen TUG 1227/17 is largest specimen of this species in collection. Maximum diameter of fragment is 15 mm in dorso−ventral diameter, 11 mm in lateral diameter, last chamber is at 13 mm dorso−ventral diameter.
Six fragments of apices are preserved. Apex is smooth, cap shaped and with faint cicatrix ( Fig. 6C View Fig ). Size of apex shows considerable variation. At second septum, dorso−ventral diameters of specimens are 0.96–1.24 mm.
Specimen TUG 1227/20 ( Fig. 4E View Fig ) is apex with four most apical chambers. Distances of apical septa beginning with initial septa are: 0.36, 0.2, 0.14. Dorso−ventral diameter at first septum is 1.04 mm, at second septum 1.2 mm, at fourth septum 1.24 mm. Siphuncle is tubular, marginal at convex side of growth axis curvature. Diameter of siphuncle at second septum is 0.1 mm with achoanitic septal neck. Connecting ring is thin.
Remarks.—The species is one of the most common cephalopods of the Siuge Member of Porkuni. It differs from Porkunioceras tuba sp. nov. in having a lower expansion rate, smooth surface and a small rounded apex.
Stratigraphic and geographic range.—Chert and dolomitised limestone of the Siuge Member, Porkuni Regional Stage, Late Ordovician from Porkuni, north Estonia.
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