Redpathoceras bullatum, Kröger, 2013

Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, European Journal of Taxonomy 41, pp. 1-110 : 88-91

Redpathoceras bullatum sp. nov.

urn:lsid:zoobank.org:act:B2601C0D-00FD-4084-B303-E0A0CB27E4A3

Figs 10G , 39 A-B, 40, 41, 42

Diagnosis

Redpathoceras with curved mature body chamber, inflated in lateral view with maximum height of ca. 60 mm at mid-length of body chamber; in longitudinal section mature body chamber conch margin at concave side of growth axis concave throughout total length; conch cross section compressed to circular in earlier growth stages; premature conch expands at 15°; diameter of terminal septum of truncation ca.

45 mm; ornamented with fine longitudinal striae and irregularly spaced transverse growth lines, which form a wide hyponomic sinus.

Etymology

From Latin bullatus, sausage, referring to the form of the mature conch of this species.

Type material

Holotype

PMU 26923 .

Paratypes

Three paratypes ( PMU 26924–26926), Kallholn, Dalarna, Sweden, Boda Limestone, Boda Core Member, late Katian.

Type locality and horizon

Kallholn, Dalarna, Sweden, Boda Limestone, Boda Core Member, late Katian, Ordovician.

Description

The holotype is an incomplete internal mould of a mature body chamber with partly recrystallised shell fragments attached ( Figs 10G , 39 A-B). The septum of truncation and parts of the phragmocone are not preserved in the holotype. The base of the body chamber is 51 mm high and 49 mm wide (height/width ratio 1.04). The dimensions of the aperture are not preserved, but its total length is estimated at ca. 105 mm. The body chamber reaches its greatest height of 60 mm at mid-length. The conch margin at the concave side of the conch curvature is curved throughout the total length of the body chamber.

The shell surface is nearly smooth with irregularly spaced growth lines, which form a broad shallow sinus on the convex side of the conch curvature. Traces of longitudinal striae are visible in parts of the surface.

The siphuncular perforation measures 5 mm (ca. 0.1 of conch height) and is positioned ca. 7 mm from the conch margin on the convex side of the conch curvature. The shell is ca. 1 mm thick at mid-length of the body chamber.

Specimen PMU 26926 is a complete, truncated portion of the phragmocone with a length at growth axis of ca. 40 mm and a conch height increasing from 33 to 44 mm (angle of expansion 15.4°) ( Figs 40 , 41 ). The shell surface is well preserved and exhibits a fine longitudinal striation. The distance of the longitudinal striae varies between 0.5 and 1 mm. Another specimen, representing the truncated part of a phragmocone (NRM Mo 152774), is 60 mm long and increases from 31 to 45 mm in height, and consists of eight chambers.

PMU 26926 ( Fig. 40 ) comprises seven chambers with successively decreasing depth and convexity in the direction of growth. The depth of the apical-most chamber is 8 mm, and its septa are deeply convex. By contrast, the adoral-most chamber is only 4 mm deep, with only a very shallow, convex septa. The septal perforation is positioned ca. 7 mm from the conch margin at the adoral-most septum. The septal necks are very unusual in being distally thickened, with the connecting rings forming an adnate attachment in the three crowded adoral-most septa. The septal necks associated with the remaining septa are suborthochoanitic. The connecting ring is thin and expanded between the chambers. The expansion of the siphuncular segments is highest in the adoral-most chambers.

Comparison

This species of Redpathoceras differs from R. magnum sp. nov. in having a smaller mature conch of maximum height of 60 mm ( Fig. 42 ), and in being entirely curved in lateral view on both the convex and concave side of the conch curvature. R. bullatum sp. nov. is larger than the type of the genus and has a less compressed conch cross section.

Stratigraphic and geographic range

Boda Limestone, late Katian, Dalarna, Sweden.

Figures

Fig. 10. Camera lucida drawings of cross sections of selected Boda Limestone cephalopods. A. Cyrtorizoceras thorslundi sp. nov., PMU 26657, Osmundsberget, mature body chamber. B. Tyrioceras cf. kjaerulfi Strand, 1934, PMU 26897, Kallholn. C. Nathorstoceras adnatum sp. nov., PMU 26733, holotype, Kallholn. D. Nathorstoceras kallholnense sp. nov., PMU 26729, holotype. E. Redpathoceras depressum sp. nov., PMU 26927, holotype, Kallholn, cross section of base of mature truncated conch. F. Schuchertoceras fryi sp. nov., PMU 24744, holotype, Kalllholn, cross section of mature aperture (dark grey) and body chamber (medium grey). G. Redpathoceras bullatum sp. nov., PMU 26923, holotype, Kallholn, cross section of base of mature truncated conch. Prosiphuncular side directed downward in all figures. Siphuncles shown as white circles. Scale bar = 10 mm for all figures.

Fig. 39. Ascocerida and Uranoceratidae of the Boda Limestone. A-B. Redpathoceras bullatum sp. nov. A. PMU 26923, holotype, Kallholn; mature truncated body chamber, lateral view. B. Same specimen, view from antispihuncular side. C. Warburgoceras longitudinale (Angelin in Angelin & Lindström, 1880) comb. nov., NRM-PZ Mo 154065, Unskarsheden; mature body chamber and part of phragmocone in lateral view. D-E. Probillingsites scandinavicum sp. nov., PMU 26922, holotype, Kallholn. D. Mature truncated body chamber, lateral view. E. Same specimen, view from prosiphuncular side. F. Schuchertoceras fryi sp. nov., PMU 24744, holotype, Kalllholn, lateral view. Scale bars: A-E =10 mm; F = 10 mm.

Fig. 40. Polished median section of Redpathoceras bullatum sp. nov., PMU 26926, Kallholn, Boda Limestone. A. Complete truncated phragmocone fragment. B. Adoral part with crowded septa and expanded siphuncular segments. C. Adapical part with wide septald distance and elongated siphuncular segments. Scale bars: A = 10 mm; B-C = 5 mm.

Fig. 41. Redpathoceras bullatum sp. nov., PMU 26926, Kallholn, Boda Limestone. A. Polished median section of detail of the septal neck and connecting ring. B. Reconstruction of A. C. Reconstruction of the total truncated fragment. Scale bar: A-B = 1 mm.

Fig. 42. Variation in angle of expansion in Redpathoceras Flower, 1963, Boda Limestone. R. magnum sp. nov. (grey dots); R. bullatum sp. nov. (black dots); R. depressum sp. nov. (black circles).