Redpathoceras saxbyense, Kröger, 2025

Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, European Journal of Taxonomy 978, pp. 1-169 : 98-100

Redpathoceras saxbyense sp. nov.

urn:lsid:zoobank.org:act:CABFDC93-1BC6-4CF4-A4EA-EF32E10648D4

Figs 36B–C, E , 37E

Diagnosis

Redpathoceras with weakly annulated mature body chamber, which is ornamented with irregularly spaced, transverse lirae or frills; exogastrically curved mature body chamber with nearly circular conch cross section at base and depressed at aperture, ca 45 mm high and 70 mm long.

Etymology

Refers to the type locality.

Type material

Holotype

ESTONIA • Vormsi Island, Saxby shore (N); Kõrgessaare FormationVormsi Regional Stage ; GIT 426- 346 .

Paratypes

ESTONIA • 2 specs; same data as for holotype; GIT 878-84 , GIT 878-156 • 1 spec.; Moe stratotype outcrop ; Moe Formation , Pirgu Regional Stage; TUG 76-97 • 1 spec.; Salu ; Pirgu Regional Stage; TUG 1745-316 • 1 spec.; Vohilaid Island, Vohilaid shore (E); Adila Formation , Pirgu Regional Stage; GIT 878-236 .

Description

GIT 426-346 ( Fig. 36B–C ) is a fragment of a mature body chamber and two chambers of the phragmocone. The outer shell is poorly preserved and apparently smooth or with fine irregular rounded lirae. The conch cross section at the base of the body chamber is nearly circular (conch height = 45 mm, conch width = 43 mm). The body chamber is 68 mm long and exogastrically curved. In lateral view, the antisiphuncular margin of the body chamber has a convex, and the prosiphuncular side a concave outline with an increasingly narrow conch cross section toward the aperture. The outline undulates slightly, resulting from a weak irregular annulation. Approximately two annulations occur on the body chamber. They are oblique, slightly shifted orad at the antisiphuncular side. At the aperture, the conch cross section is depressed with a height of 35 mm and a width of ca 25 mm, respectively. The sutures are directly transverse and 6 mm apart where the conch height is 45 mm (RCL = 0.13). There, the septal foramen has a diameter of 4.5 mm and is 5 mm distant from the conch margin.

GIT 878-156 is a weakly exogastrically curved fragment of a phragmocone and part of a body chamber showing the details of the siphuncle and septal necks ( Fig. 37E ). The phragmocone height increases from 34 mm to 41 mm at a length of 27 mm (angle of expansion = 15°). The conch cross section is slightly compressed (CHI = 1.07). The septa form directly transverse sutures, 7 mm apart where the conch height is 37 mm (RCL = 0.19). The septal foramen is ca 4.5 mm in diameter and ca 5 mm distant from the conch margin (RSH = 0.12, RSP = 0.16). The siphuncular segments are nearly tubular and the septal necks are loxochoanitic dorsally and suborthochoanitic ventrally.

In TUG 76-97 ( Fig. 36E ), and TUG 1745-316 the conch surface of the mature body chamber is well-preserved. In the three specimens, the shell is slightly irregularly annulated, similar to GIT 426-346. Additionally, the conch surface is ornamented with irregularly spaced rounded lirae (ca one to two per millimeter) which are slightly shifted orad on the dorsum.

Comparison

This species of Redpathoceras differs from other species of the genus in having a weakly annulated and transversally frilled mature body chamber. A specimen, assigned by Evans (1993) to Charactoceras ? cinerum ( Blake, 1882), probably represents another similarly ornamented species of Redpathoceras , which has, however, a larger adult size (mature body chamber 60 mm wide and 200 mm long).

The possibility exists that the specimens described herein are related to Piersaloceras gageli Teichert, 1930 , which is known only from a single immature fragment, or to another, yet to be discovered species of Piersaloceras . This is suggested based on the similar ornamentation and similar position of the siphuncle. If this is the case, Piersaloceras could be interpreted as an uranoceratid or probillingsitid. The strongly curved, isolated, body chamber described herein under Piersaloceras (?) sp. ( Fig. 30C ), would support such a hypothesis. Because of the fragmentary character of the known specimens, however, this relation must remain speculative, for now.

Figures

Fig. 36. Ascoceratidae Barrande, 1867 and Uranoceratidae Hyatt, 1900 of the Vormsi–Pirgu regional stages, Estonia. A. Deckeroceras balticum sp. nov., holotype GIT 878-227, from Vohilaid shore (E), Vohilaid Island, Pirgu Regional Stage, lateral view. B–C. Redpathoceras saxbyense sp. nov., holotype GIT 426-346, Saxby shore (N),Vormsi Island, Vormsi Regional Stage.B. View of the prosiphuncular side. C. Lateral view. D. Schuchertoceras deformis (Eichwald, 1860), specimen GIT 878-191, from Vohilaid shore (E), Vohilaid Island, Pirgu Regional Stage, oblique lateral view. E. Redpathoceras saxbyense sp. nov., paratype GIT 76-97, from Moe stratotype outcrop, Pirgu Regional Stage.F–G. Schuchertoceras deformis (Eichwald, 1860), specimen TUG 2-734, Uuemõisa, Läänemaa, Pirgu Regional Stage. F. View of the antisiphuncular side. G. Lateral view. Scale bar = 20 mm, same scale in all figures.

Fig. 37 (next page). Median sections of phragmocones of Multiceratoidea Mutvei, 2013 of the Vormsi– Pirgu regional stages, Estonia. A. Kiaeroceras sp. E, specimen GIT 878-21 from Saxby shore (N), Vormsi Island, Vormsi Regional Stage. B. Cyrtogomphoceras troedssoni Teichert, 1930, specimen TUG 939-60, from Kõrgessare, Hiiumaa Island, Vormsi Regional Stage (section is approximate median only). C. Hosholmoceras ovalis gen. et sp. nov., holotype GIT 840-252, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage (section is approximate median only). D. Kiaeroceras (?) ormsoense sp. nov., holotype GIT 878-63, from Saxby shore (N), Vormsi Island, Vormsi Regional Stage. E. Redpathoceras saxbyense sp. nov., specimen GIT 878-156, from Saxby shore (N), Vormsi Island, Vormsi Regional Stage. F. Kiaeroceras kaebliki sp. nov., paratype GIT 426-1123, from Saxby shore, Vormsi Island, Vormsi Regional Stage. G. Lyckholmoceras norvegiae Strand, 1934, specimen GIT 878-187, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. H. Kiaeroceras kaebliki sp. nov., holotype GIT 878-31, Saxby shore (N), Vormsi Island, Vormsi Regional Stage. Scale bars = 5 mm in all figures.

Fig. 30. Graciloceratidae Flower, 1950 and Oncoceratidae Hyatt, 1884 of the Vormsi–Pirgu regional stages, Estonia. A. Beloitoceras siljanense Frye, 1987, specimen TUG 939-56 from Haapsalu holm, Pirgu Regional Stage, lateral view. B. Rizosceras teres sp. nov., paratype GIT 426-550, from Kõrgessaare quarry, Vormsi Regional Stage, lateral view. C. Piersaloceras (?) sp., specimen TUG 1827-163, from Sutlema old quarry, Vormsi Regional Stage, lateral view. Scale bar = 20 mm, same scale in all figures.