Buttsoceras buldrebreenense Kröger & Pohle 2021, sp. nov

Buttsoceras buldrebreenense sp. nov

urn:lsid:zoobank.org:act: D6C02A7F-2CAF-44FC-A243-52AB01FCEB2C

Figs 9A–B, D–E, 11B, 34–35

Diagnosis

Smooth orthocones with elliptically compressed conch cross sections, widely spaced chambers (relative chamber length up to ca 0.6); with large siphuncles (rSD = 0.25) which are slightly expanded into the chambers and are eccentrically positioned (rSP = 0.21); septal necks are short orthochoanitic; continuous endosiphuncular lining and episeptal deposits are present.

Etymology

From Buldrebreen, a glacier near Olenidsletta, Ny Friesland, Svalbard close to the type locality of the specimen.

Type material

Holotype Specimen FMNH-P30421.

Paratypes Four specimens (FMNH-P30422, P30423, P30428, P30430) from type locality and horizon.

Type locality and horizon

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

Description

The holotype, FMNH-P30421, is a 44 mm long, nearly straight fragment of a phragmocone with a smooth conch surface and a compressed conch with a height of 16.7–17.3 mm and a width of 14.8– 16 mm (rW ≈ 0.9, angle of expansion of conch height 2°) (Fig. 9E). The angle of expansion is 5° in specimen FMNH-P30430, which has a conch height of 21–23 mm.

The conch surface is almost smooth with faint, irregularly spaced growth lines which may form striae with a distance between 1 and 2 mm in the holotype. The growth bands or growth lines are obliquely transverse, shifted adorally at the antisiphuncular side of the conch (visible in specimen FMNH-P30423 and in holotype, Fig. 9D–E).

The diameter of the septal perforation of the holotype is ca 0.25 of the corresponding conch height and positioned between the center and conch margin with an rSP of 0.21. This is identical to the mean of the rSP of all five measurements from the available specimens (mean se = 0.21; minimum measured rSP = 0.21, maximum measured rSP = 0.21; n = 5). The mean relative siphuncular diameter of all measured specimens is 0.25 (range of rSD: 0.23–0.28; n = 6) (Fig. 34).

The sutures are directly transverse. The relative chamber length varies between 0.26 and 0.58 in four measured specimens (FMNH-P30421, P30422, P30423, P30430) and decreases with conch height (Fig. 34).

The septal necks are short, orthochoanitic, and in the holotype 0.6 mm long where the corresponding chamber length is ca 5 mm.The connecting ring is thin, and its segments expand slightly into the chambers (Figs 11B, 35A). The siphuncle is completely filled with endosiphuncular deposits in the holotype at a conch height of 14 mm and 16 mm, leaving only a questionable 0.6 mm central canal. At a conch height of 17 mm the ventral half of the siphuncle is completely filled with a massive endosiphuncular deposit. In the holotype, episeptal deposits are developed at the pro-siphuncular (ventral) side of the conch.

Comparison

This species is unique among species of Buttsoceras with regard to its elliptically compressed conch cross section. The type species of Buttsoceras, B. adamsi, differs in having a nearly circular to slightly depressed conch cross section and a transversally striated conch surface. The center of the siphuncle of this species is at a position with a distance of ca 0.35 of the conch height from the conch margin; this is more eccentric than in the specimens of Buttsoceras sp. of the Croisaphuill Formation (late Floian Stage), Scotland, UK (compare Evans 2011).