Hinlopoceras tempestatis, 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 : 24-26

Hinlopoceras tempestatis gen. et sp. nov.

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Figs 17D–F, I , 18 , 19B

Diagnosis

Hinlopoceras gen. nov. with cross section changing from circular in juvenile growth stage to ca 0.9 in adult specimen; angle of expansion decreases during growth from ca 14° to 10°; ornamented with distinct directly transverse, irregularly spaced lirae, 1.5–3 lirae occur per millimeter, and with weak, directly transverse annulations in latest growth stages. Siphuncle narrow with diameter 0.15 of corresponding conch height, strictly marginally positioned.

Etymology

From the Latin ‘ tempestas ’, ‘storm’; referring to its wave-like distinct transversely lirate ornamentation.

Type material

Holotype Specimen FMNH-P30360 .

Paratypes Fifteen specimens ( FMNH-P30450 , P30357 to P30359 , P30260 to P30269 , P30479 ) all are from type locality and type horizon.

Type locality and horizon

From Profilstranda section, adjacent to Hinlopenstretet, Spistbergen, from bed PO 07, 4.0 m above base of Olenidsletta Member, V 1a trilobite zone, Blackhillsian, Floian.

Description

The conch is curved and has a cross section that changes from circular during early growth stages, with diameters less than 10 mm, to slightly compressed (rCW ca 0.9) in later growth stages ( Fig. 18 ). The conch expands in conch height with an angle of 9°–14° and in conch width from 9° to 13°. The conch curvature also decreases adorally, with specimens> 10 mm in conch height having a nearly orthoconic conch with an angle of expansion of ca 10° ( Fig. 18 ).

The conch ornament consists of distinct, directly transverse lirae which are relatively widely spaced and form a shallow hyponomic sinus on the concave side of the conch curvature ( Figs 17D , 19B ). In specimen FMNH-P30268 the distance between lirae is 0.3 mm to 1 mm where the conch height is 7 mm, and sometimes several subordinate finer lirae occur between two more pronounced lirae.

Two specimens have the siphuncle preserved; in the holotype the siphuncle is marginally positioned at the concave side of the conch curvature, and 0.4 mm wide where the conch cross section is 2.9 mm. In specimen FMNH-P30365 the siphuncle has a diameter of 1.2 mm where the conch cross section is 7.2 mm. The chamber length is known from two specimens only; in the holotype the chamber length is 0.7 mm at a corresponding conch height of 3 mm, and in FMNH-P30269 the septa have a distance of 1 mm where the conch is 3.7 mm in diameter. The largest fragments (specimens FMNH-P30358, FMNH-P30362) have maximum conch heights of 16.4 mm and 17 mm, respectively, and are ornamented additionally with a weak transverse annulation, which is more pronounced adorally. The distance between the rounded annuli is ca 3 mm and ca seven lirae occur per cycle of annulation.

Comparison

See comparison of Hinlopoceras venti gen. et sp. nov.

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.