Ancistroceras undulatum ( Boll, 1857 )

Aubrechtová, Martina & Korn, Dieter, 2022, Taxonomy and ontogeny of the Lituitida (Cephalopoda) from Orthoceratite Limestone erratics (Middle Ordovician), European Journal of Taxonomy 799 (1), pp. 1-108 : 29-31

Ancistroceras undulatum ( Boll, 1857)

Figs 17–18 , Tables 5–6

Lituites undulatus Boll, 1857: 87 .

Ancistroceras undulatum – Boll 1857: pl. 8 fig. 25a. — Dewitz 1880: 387, pl. 17 fig. 5. — Holm 1885: 21, pl. 3 fig. 2, pl. 4 figs 1, 3–20. — Patrunky 1926: 120. — Foerste 1930: 272, pl. 41 figs 1a–b, 3a–b, 4a–c, pl. 42 figs 3–4. — Balashov 1953: 236, pl. 14 figs 5a–b, 8. — Sweet 1958: 129, pl. 13 figs 2–3, 5, pl. 18 fig. 1. — Zhuravleva 1961: pl. 12 figs 2–3. — Aubrechtová & Meidla, 2020: 272, text-figs 5–6.

Strombolituites undulatus – Remelé 1881: 191, text-fig. 1; 1882: 11, pl. 5 fig. 1.

Ancistroceras cf. undulatum – Schindewolf 1942: 348, text–fig. 4c.

non Ancistroceras undulatum – Noetling 1884: pl. 18 fig. 6–6a. — Rüdiger 1889: 44. — Balashov 1953: pl. 14 figs 6–7. — Neben & Krueger 1971: pl. 17 fig. 1. — Qi 1980: 254, pl. 2 fig. 6, text-fig. 5.

non Ancistroceras cf. undulatum – Chen 1987: 178, pl. 6 fig. 18, text-fig. 38.

Diagnosis

Species of the genus Ancistroceras with a moderately curved end of the coiled part of the conch; uncoiled part conical with an expansion angle of 25–27°. Whorl profile circular throughout ontogeny. Relative chamber length ca 0.35. Ornament with wide and low annuli (spaced at 2 mm distance after uncoiling and 4 mm distance in later growth stages) and lirae (0.5 mm in distance after uncoiling and 0.5–1 mm in distance in later growth stages); crests of annuli commonly with raised pairs of lirae. Course of the lirae with ventral sinus and lateral sinus; dorsal projection roof-shaped and flanked by shallow dorsolateral sinuses. Position of the siphuncle slightly more dorsad in the juvenile part of the conch and gradually relocated to central or almost central position. Connecting rings thin, slightly expanded, siphuncular segments thus slightly constricted at the septal necks (after Aubrechtová & Meidla 2020, emended).

Type material

Holotype not available for study; Boll (1857: pl. 8 fig. 25) figured one specimen from Usadel near Neubrandenburg (Mecklenburg-Vorpommern, Germany), found in erratics from Pleistocene gravel (Uhaku Regional Stage, late Darriwilian, Middle Ordovician).

Material examined

GERMANY • 1 spec.; Brandenburg, Niederfinow; Ordovician, Upper Grey Orthoceratite Limestone; Neben 1936 Coll.; MB.C.11696 • 2 specs; Brandenburg, Oderberg; Ordovician, Upper Grey Orthoceratite Limestone; Neben and Krueger Coll.; MB.C.30520 , MB.C.30521 .

POLAND • 1 spec.; West Pomerania, Juszkowo (former Gischkau); Ordovician, Upper Grey Orthoceratite Limestone; Neben and Krueger Coll.; MB.C.30522 • 1 spec.; West Pomerania, Skowarcz (former Schönwarling), Gdańsk County; Ordovician; Hoyers 1912 Coll.; MB.C.11697 .

Description

The five specimens are fragments of the uncoiled parts of conchs (only the very end of the coiled parts are preserved). The conchs expand with angles of 25–27° ( Fig. 19A ). The largest specimen is MB.C.30520, which attains 57 mm whorl height; at this size, the whorl profile is circular with centrally located siphuncle and an SDR of 0.13 ( Fig. 19B ). The shell ornament is preserved in all specimens. It consists of annuli (up to 3.5 mm apart), which bear raised pairs of lirae (up to 1 mm apart) on their crests. The ornament elements form a ventral sinus, lateral sinuses and a dorsal projection that is roof-shaped and flanked by low dorsolateral sinuses ( Figs 17–18 ).

Remarks

Ancistroceras undulatum is very similar to A. barrandei (described below), from which it differs chiefly in the weaker curvature at the end of the coiled part of the conch ( Aubrechtová & Meidla 2020). However, the present material reveals further differences in the shell ornament: the dorsal projection is roof-shaped, flanked by low dorsolateral sinuses in A. undulatum . By contrast, the dorsal projection in A. barrandei is continuously rounded and lacks dorsolateral sinuses.

Specimen MB.C.11687 is the largest Ancistroceras in the collection with the length of 226 mm and maximum whorl height of 49 mm. The conch is, however, incompletely preserved and the specimen is thus assigned to A. cf. undulatum .

A regular network of radial lines and impressions is preserved in the posterior surface of cameral deposits in the specimen MB.C.11696. These were interpreted as remains of a vascular system by Aubrechtová & Meidla (2020: fig. 5f–g). The same structures are found also in the specimen MB.C.11697a ( Fig. 17 ).

Geographic and stratigraphic occurrence

Norway, Sweden, Estonia (in situ) and northern Germany, northern Poland and the Kaliningrad Region ( Russia) (in erratics within Pleistocene gravels); Lasnamägi, Uhaku and early Kukruse regional stages (Darriwilian to early Sandbian, Middle to early Late Ordovician).

Ancistroceras undulatum is a stratigraphically significant species in Baltoscandia indicating the Uhakuan age (e.g., Jaanusson 1960; Evans et al. 2014).

Figures

Fig. 17. Ancistroceras undulatum (Boll, 1857) from the Upper Grey Orthoceratite Limestone; specimen MB.C.11697a (Hoyers 1912 Coll.) from Skowarcz (former Schönwarling); previously figured by Foerste (1930: pl. 41 fig. 1); dorsal, lateral and ventral views. Note imprints of the vascular system near the apex visible in the photograph on the left. Scale bar units = 1 mm.

Fig. 18. Ancistroceras undulatum (Boll, 1857), lirae course in selected specimens. A. Specimen MB.C.30522 (Neben & Krueger Coll.) from Juszkowo (former Gischkau), Gdańsk County (Pomerania, Poland), at wh = 10 mm. B. The same specimen, at wh = 27 mm. C. Specimen MB.C.30521 (Neben & Krueger Coll.) from Oderberg (Brandenburg), at wh = 18 mm. Scale bar units = 1 mm.

Fig. 19. Conch expansion rates (A) and siphuncle diameter rates (B) in species of Ancistroceras Boll, 1857.