Redpathoceras depressum, Kröger, 2013

Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, European Journal of Taxonomy 41, pp. 1-110 : 91-92

Redpathoceras depressum sp. nov.

urn:lsid:zoobank.org:act:C6767BCC-4FD2-4A7E-BE5C-F4738889A43E

Figs 10E , 18G , 42 , 43 D-F

Diagnosis

Redpathoceras with curved mature body chamber; inflated in lateral view with maximum height of ca. 55 mm at mid-length of body chamber; mature body chamber margin at concave side of conch curvature concave throughout total length; conch cross section depressed; premature conch expands with angle of expansion less than 10°; 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

Refers to the distinctively depressed conch cross section of this species.

Type material

Holotype

PMU 26927 .

Paratypes

Seven paratypes ( PMU 26928–26934), Kallholn, Dalarna, Sweden, Boda Limestone, late Katian.

Type locality and horizon

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

Description

The holotype is a nearly complete mature conch, 120 mm long. The conch is depressed with a height of 41 mm and width of 48 mm at the septum of truncation (width/height ratio 1.2). At the aperture, these measurements are 50 mm and ca. 65 mm, respectively (width/height ratio 1.3; Figs 10E , 43D, F ). The mature conch is moderately curved. The convex side of the conch curvature is more strongly curved than the concave side, resulting in a maximum conch height at approximately the mid-length of the mature body chamber of 55 mm. Immediately adoral to the septum of truncation the conch appears to be a slighty constricted. The length of the phragmocone and the numbers of chambers of the phragmocone are not known, as the conch wall obscures details of the septa. The outermost layer of the shell is poorly preserved, with no traces of the ornamentation remaining ( Fig. 18G ).

Four specimens (PMU 26930–26933) represent truncated portions of the phragmocone. All four specimens possess at their apical end a deeply curved septum of truncation. The conch height at the septum of truncation varies between 23 and 28 mm and the adoral-most diameters lie between 36 and 38 mm, giving angles of expansion ranging from 6 to 8° ( Fig. 42 ). The conch cross section in these specimens is depressed (width/heigh ratio 1.03–1.16) and they are more curved than the mature fragment (holotype). In specimen NRM Mo 152301 the entire length comprises seven chambers. The suture is nearly directly transverse, but forms a shallow, wide lobe on the convex side of the conch curvature. All four specimens are distinctively ornamented with fine longitudinal striae and fine, irregularly spaced growth lines, forming a wide sinus on the convex side of the conch curvature.

Comparison

This species of Redpathoceras is similar to the type of the genus in having a depressed conch cross section, but differs in having a larger adult size. The adult size is similar to that seen in R. bullatum sp. nov., which in turn differs in having a circular-compressed conch cross section in premature growth stages.

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. 18. Shell ornamentation of selected Cephalopoda of the Boda Formation. A. Order, gen. et sp. indet., PMU 26950, Kallholn, lateral view. B. Palaeodawsonocerina? nicolletoides sp. nov., PMU 26727, holotype, Kallholn. C. Palaeodawsonocerina senckenbergi (Teichert, 1930), PMU 26718, Kallholn. D. Geisonoceras wegelini (Angelin in Angelin & Lindström, 1880) comb. nov., PMU 26745, Unskarsheden. E. Pleurorthoceras osmundsbergense sp. nov., NRM-PZ Mo 150126, holotype, Osmundsberget. F. Warburgoceras longitudinale (Angelin in Angelin & Lindström, 1880) comb. nov., NRM-PZ Mo 154065, Unskarsheden. G. Redpathoceras depressum sp. nov., PMU 26931, Kallholn. Scale bar = 5 mm for all figures.

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).

Fig. 43. Redpathoceras Flower, 1963, Kallholn, Boda Limestone. A-C. Redpathoceras magnum sp. nov. A. PMU 26935, holotype; mature truncated body chamber, lateral view. B. Same specimen, view from antispihuncular side. C. PMU 26946, premature truncated phragmocone, lateral view. D-F. Redpathoceras depressum sp. nov. D. PMU 26927, holotype; mature truncated body chamber, lateral view. E. Same specimen, view from antispihuncular side. F. PMU 26931, premature truncated phragmocone, lateral view. Scale bar = 50 mm for all figures.