Proterocameroceras valhallfonnense Kröger & Pohle 2021, sp. nov.

Proterocameroceras valhallfonnense sp. nov.

urn:lsid:zoobank.org:act: A94148C2-2CBC-438E-B4C9-36EAE5161A76

Figs 9H–I, 10B–D, 11C

Diagnosis

Slender orthocones with smooth shell and with weakly depressed conch cross section with a relative conch width (rW) of ca 1.1–1.2; chambers are relatively widely spaced, ca four–six chambers occur per distance similar to the corresponding conch height; the siphuncle is ca ⅓ of the diameter of the corresponding conch height.

Etymology

From Valhallfonna Glacier, referring to the type region of this species.

Type material

Holotype Specimen FMNH-P30427.

Paratypes Specimens FMNH-P30277 and P30429 from type locality and horizon.

Type locality and horizon

Profilstranda section, adjacent to Hinlopenstretet, Spitsbergen, bed PO 131, 128 m above base of Olenidsletta Member, V 2b trilobite zone, Blackhillsian, Floian.

Description

The holotype is the most complete fragment of this species; it is a 21 mm long fragment of a phragmocone which grows from 10–12 mm in conch height with an angle of expansion of 5.5° (Fig. 9H–I). It has a slightly depressed conch cross section and a well-preserved smooth conch surface. The chambers have a distance of ca 2.5 mm at a corresponding conch height of 10 mm (rCL = 0.25). The diameter of the siphuncle is 4 mm (rSD = 0.4) with slightly concave siphuncular segments. The connecting ring is poorly preserved but where visible of moderate thickness. The septal necks are loxochoanitic to orthochoanitic with a length of ca 0.28 of the corresponding chamber length. The siphuncle is filled with asymmetric endocones which are more pronounced and reach ca 30 mm toward the aperture at the ventral side and only ca 15 mm at the dorsal side (Fig.10C).

The shell of the other two specimens is slender, orthoconic with a smooth surface and a slightly elliptically depressed cross section. In specimen FMNH-P30277 a conch height of 13.5 mm relates to a width of ca 14.5 mm, and in the specimen FMNH-P30429 the conch height is 17 mm, where the conch width is 20 mm (rW = 1.07, 1.18 respectively).

The siphuncle is circular in cross section and positioned close to the conch margin, with a diameter of 5 mm in specimen FMNH-P30277 and 6 mm in specimen FMNH-P30429 (rSD = 0.37 and 0.35, respectively). The exact angle of expansion cannot be measured in either specimen because of the fragmentary preservation.

In specimen FMNH-P30277 the preserved septum is obliquely transverse, shifted toward the aperture at the antisiphuncular side of the conch. The suture forms a broad saddle at the lateral flanks, a broad shallow lobe at the dorsum and a pronounced broad u-shaped lobe at the venter. More details of septa and siphuncle are preserved in the specimen FMNH-P30429, which has a chamber distance of 3 mm (ca six chambers occur per distance similar to the corresponding conch height) and loxochoanitic to orthochoanitic septal necks which are ca 0.7 mm long, where measurable (Figs 10D, 11C). The shape of the siphuncular segments and the thickness of the connecting ring cannot be determined with certainty in specimen FMNH-P30277 because of poor preservation.

Comparison

The placement of this new species in Proterocameroceras is somewhat provisional, because the endosiphuncular deposits are poorly known and preserved. Characters of the endocones, such as the presence of endosiphoblades (Teichert 1964: K166) and of an endosiphotube (Ulrich et al. 1944) are explicitly mentioned in the genus diagnosis (see above), but they are not preserved in the material described herein. Furthermore, P. valhallfonnense sp. nov. differs from the type species and from other Early Ordovician species of Proterocameroceras in having relatively widely spaced septa. In P. brainerdi, e.g., ca 10–12 chambers occur at a distance similar to the corresponding diameter.

Two species assigned to Proterocameroceras from the Middle Ordovician of the Baltica paleocontinent, from Mishina Gora, western Russia, have a septal spacing which is comparable to that of P. valhallfonnense. Of these, P. gdovense Balashov, 1968 differs in having nearly tubular siphuncular segments and a thin connecting ring, and P. mishinagorense Balashov 1968 has a lower angle of expansion. In both species from western Russia the siphuncle is narrower, measuring only ca ⅓ of the conch diameter (Balashov 1968).