Redpathoceras Flower, 1963

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

Genus Redpathoceras Flower, 1963

Type species

Redpathoceras clarki Flower, 1963 , northeast of Joliette, Quebec, Canada; Leray Limestone, early-mid Katian, Ordovician; by original designation.

Diagnosis

Gyrocones with circular to depressed mature conch cross section; mature body chamber inflated with greatest diameter at approximate mid-length; broad shallow hyponomic sinus; septum of truncation deeply rounded; suture of septa in mature specimen slightly oblique, sloping in adoral direction on concave side of conch curvature; siphuncle eccentric, close to conch margin at convex side of conch curvature. (Adopted from Flower 1963.)

Remarks

Redpathoceras was assigned to the Probillingsitidae by Flower (1963) because of its deeply rounded septum of truncation and its inflated mature body chamber. The type species, Redpathoceras clarki , is characterized by a mature shell with only two chambers adoral of the terminal truncation; this is similar to Probillingsites . Some specimens of Redpathoceras from the Boda Limestone have mature truncated shells with five chambers ( Redpathoceras magnus sp. nov.); this is very similar to Montyoceras Flower, 1941 , and supports Flower’s (1963) hypothesis of an ancestry of Billingsites and other ascocerids from a Montyoceras -like form. (The truncated parts of premature Redpathoceras phragmocones consist of ca. seven to eight chambers.)

On the other hand, the strongly curved conch portions of Redpathoceras are very similar to some uranoceratids, such as Deckeroceras Foerste, 1935 , Siljanoceras gen. nov. and Warburgoceras gen. nov., from which it mainly differs in having a deeply convex septum of truncation. This suggests a relationship of Uranoceratidae with ascocerids (see discussion below).

The shape of the septal necks and connecting ring of the species of Redpathoceras known from the Boda Limestone are similar to those of Probillingsites (compare with Furnish & Glenister 1964a: fig. 189.4; Fig. 40 A-C). The connecting ring is slightly expanded in juvenile chambers and nummoidal and strongly expanded in the latest chambers. The septal necks are suborthochoanitic in juvenile stages and distally thickened and achoanitic in the latest stages.

Stratigraphic and geographic range

Leray Limestone, early-mid Katian, Quebec, Canada; Boda Limestone, late Katian, Dalarna, Sweden.

Figures

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.