Hinlopoceras venti, Kröger & Pohle, 2021

Kröger, Björn & Pohle, Alexander, 2021, Early-Middle Ordovician cephalopods from Ny Friesland, Spitsbergen - a pelagic fauna with Laurentian affinities, European Journal of Taxonomy 783 (1), pp. 1-102 : 26-29

Hinlopoceras venti gen. et sp. nov.

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Figs 17G–H, J , 18 , 19A

Diagnosis

Hinlopoceras gen. nov. with cross section changing from circular in juvenile growth stage to slightly compressed (rW ≈ 0.8) in adult specimen; angle of expansion decreases during growth from ca 14° to 11°; ornamented with distinct irregularly spaced directly transverse lirae which are more pronounced during later growth stages. Siphuncle narrow with rSD = 0.12, strictly marginally positioned and with loxochoanitic septal necks.

Etymology

From Latin ‘ ventus ’, ‘wind’; referring to its wave-like faint transversely lirate ornamentation.

Type material

Holotype Specimen FMNH-P30266 .

Paratypes Two additional specimens from the type locality: FMNH-P30267 from bed PO 7.5 and FMNH-P30262 from bed PO 07 , 4.5 m and 4.0 m above the base of Olenidsletta Member, V1 a trilobite zone, Blackhillsian , Floian .

Type locality and horizon

From Profilstranda section, adjacent Hinlopenstretet, Spitsbergen, from bed PO 7.5, 4.5 m above base of Olenidsletta Member, V 1a trilobite zone, Blackhillsian, Floian.

Description

The conch is curved in growth stages less then ca 10 mm, and almost orthoconic in later growth stages; its conch height increases at an angle of 14° in early growth stages and 11°–13° in later growth stages ( Fig. 18 ). The degree of compression increases during growth, with specimens> 10 mm in conch height with rW ≈ 0.9 or less ( Fig. 18 ).

The ornament consists of transverse lirae which are less pronounced and faint during early growth stages; conch almost smooth in growth stages with conch height <7 mm; at conch height>ca 9 mm the lirae are well expressed, with a distance of ca 0.3–0.6 mm (specimens FMNH-P30266, P30267). In specimen FMNH-P30262 the distance between two major lirae is 0.7 mm with one subordinate lira in between at a conch height of ca 14 mm ( Fig. 19A ).

The siphuncle is preserved in the adapical part of specimen FMNH-P30266, where the conch diameter is 3.4 mm and the siphuncular diameter is 0.4 mm.

Comparison

Hinlopoceras venti gen. et sp. nov. differs from H. tempestatis gen. et sp. nov. mainly in its less pronounced ornamentation, which is faint during early growth stages and consists of irregularly spaced transverse lirae of different strength in growth stages with conch height larger than ca 8–9 mm. Hinlopoceras tempestatis gen. et sp. nov. has pronounced lirae throughout its entire growth (except the very adapical ca 10 mm, Fig. 17I ) and a clear differentiation between primary and secondary lirae exists throughout its growth. Little is known about the internal characters of H. venti gen. et sp. nov. because all specimens of the sample have a strongly recrystallized phragmocone. The general similarity of this species with H. tempestatis gen. et sp. nov., however, suggests a similar chamber spacing, siphuncular position and shape.

Figures

Fig. 17 (previous page). Rioceratid and orthocerid cephalopods from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. A-C. Eosomichelinoceras borealis sp. nov., from bed PO 123.3. A. Specimen FMNH-P30278, lateral view with ventral, prosiphuncular side toward left.B. Specimen FMNH-P30279, lateral view with ventral, prosiphuncular side toward left. C. Specimen FMNH-20288, holotype, ventral view. D–F, I. Hinlopoceras tempestatis gen. et sp. nov., from bed PO 07. D. Specimen FMNH-P30359, lateral view with ventral, prosiphuncular side toward right.E. Specimen FMNH-30479, adult(?) body chamber, ventral view, prosiphuncular side.F. Specimen FMNH-P30362, strongly annulated fragment of body chamber. G–H, J. Hinlopoceras venti gen. et sp. nov. G. Specimen FMNH-P30262, from bed PO 07, lateral view with ventral, prosiphuncular side toward left. H. Specimen FMNH-P30266, from bed PO 7.5, lateral view with ventral, prosiphuncular side toward right. I. Specimen FMNH-P30360; note the nearly smooth adapical part of the fragment. J. Specimen FMNH-P30267, from bed PO 7.5, lateral view with ventral, prosiphuncular side toward left. Scale bar = 10 mm for all figures.

Fig. 18. Diagrams of relative conch width and angles of expansion of species of Hinlopoceras gen. nov. from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. See Supp. file 1 for details of measurements.

Fig. 19. Details of the conch surface of rioceratid cephalopods from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. A. Hinlopoceras venti gen. et sp. nov., FMNH- P30262, from bed PO 07, lateral view with ventral, prosiphuncular side toward left. B. Hinlopoceras tempestatis gen. et sp. nov., FMNH-P30359, from bed PO 07, lateral view with ventral, prosiphuncular side toward right. C. Svalbardoceras skua gen. et sp. nov., FMNH-P30408, from bed PO 123.3. D. Svalbardoceras sterna gen. et sp. nov., FMNH-P30373, from bed PO 7.5. Scale bar = 5 mm for all figures.