Coeloterorhynchus dillanus ( Schmidt, 1941 )

Baliński, Andrzej, 2006, Brachiopods and their response to the Early-Middle Frasnian biogeochemical perturbations on the South Polish carbonate shelf, Acta Palaeontologica Polonica 51 (4), pp. 647-678 : 663-666

Coeloterorhynchus dillanus ( Schmidt, 1941)

Figs. 13 , 14D–F .

1941 Pugnax acuminatus dillanus n. subsp.; Schmidt 1941: 284–285, pl. 1: 2–4.

1971 Coeloterorhynchus dillanus (Herta Schmidt, 1941) ; Brice 1971: 79, pl. 3: 7–9; fig. 3.

1988 “ Parapugnax ” sp.; Makowski 1988: pl. 12: 3, 4, 6, 13, 14.

1990 Coeloterorhynchus dillanus ( Schmidt, 1941) ; Budziszewska 1990: 32–33, pl. 5: 1, 2.

1990 Coeloterorhynchus magnificum Cooper and Dutro, 1982 ; Budziszewska 1990: 33–35, pl. 6: 1–4.

1993 “ Parapugnax ” sp.; Makowski in Racki et al. 1993: pl. 8: 5.

Material.—55 more−or−less complete shells that are usually strongly exfoliated and 65 fragments. Most of the collection comes from bed 14 of set C in Wietrznia Id−W section and beds 44 and 45 of the same set in Wietrznia Ie section (see Figs. 2 and 3 for details).

Description.—Shell medium to large sized, wider than long, transversely elliptical in outline, strongly dorsibiconvex; cardinal margin broadly arched to slightly angular, lateral margins rounded, anterior margin truncate to slightly emarginate, anterior commissure strongly uniplicate.

Ventral valve with weakly convex flanks and deeply excavated wide sulcus originating about 7–8 mm from the umbo; tongue high, rounded and serrate, with concave to flat, costate bottom, in large shells slightly bent dorsally.

Dorsal valve strongly domed in anterior view; in lateral view it is posteriorly convex but flattened in anterior region; fold very high but laterally smoothly grades into flanks, which are strongly expanded ventrally.

Shell surface smooth except for marginal parts of valves which are costate; flanks with up to five usually weak costae, fold with 2–6 costae (usually 3 or 4), sulcus with 1–5 costae (usually 2 or 3), costae on fold shorter but stronger than those in sulcus. Microornamentation rarely observed, in the form of extremely weak radial capillae and concentric growth lines seen on preserved patches of the primary shell layer. However, the traces of the capillae can be also recognised on specimens with exfoliated primary layer but with well preserved external surface of the fibrous secondary shell layer.

Interior of the ventral valve with short subparallel to slightly divergent dental plates. Dorsal valve without median septum but with short median thickening or ridge ( Fig. 13 ); hinge plates discrete.

Remarks.—The specimens from Wietrznia show great variability in general shell dimensions and shape, degree of its costation, and in width and depth of the ventral sulcus. They have a close affinity to Coeloterorhynchus dillanus ( Schmidt, 1941) which was described from the Frasnian Iberger Kalk of Germany. Unfortunately, the species was inadequately figured by that author thus making the assessing range of its variability difficult. It seems, however, that both forms have the same shell shape, outline, costation and similarly developed ventral sulcus and tongue. Some specimens from Wietrznia have stronger median costae but this difference might be immaterial from the reason mentioned above. The specimens described here demonstrate considerable variability in width of the ventral sulcus which may be wider or narrower than that in the German specimens.

The specimens of Coeloterorhynchus dillanus described from the Frasnian of Morocco by Brice (1971) are generally very similar to type specimens from Germany and to the specimens here described but differ mainly by apparently more compressed shell laterally .

Polish specimens are also similar in many respects to Coeloterorhynchus magnificum Cooper and Dutro, 1982 described from the Sly Gap Formation of New Mexico (see also Budziszewska 1990). Minor differences are seen only in greater shell dimensions and occasionally in slightly wider shell attained by some of the studied specimens. It seems that both forms are very close.

Occurrence.—This is fairly common species in set C of Wietrznia Id−W and Ie sections. These occurrences represent Palmatolepis transitans conodont Zone. It was originally described from the Iberger Limestone of Langenaubach and Winterberg, Germany ( Schmidt 1941). The species was apparently also recovered by the present author in the Frasnian brachiopod limestone of Elbingerode, Germany.

Figures

Fig. 13. Serial sections of two shells of Coeloterorhynchus dillanus (Schmidt, 1941), ZPAL Bp 60/32 (A) and ZPAL Bp 60/33 (B), middle Wietrznia Beds of Wietrznia Ie. Numbers refer to distance in mm from ventral umbo.

Fig. 14. Rhynchonellid brachiopods from the middle Wietrznia Beds of Wietrznia Ie (A) and Id−W (B–F). A–C. Coeloterorhynchus schucherti (Stainbrook, 1945), ZPAL Bp 60/7 (A), GIUS 4−273 Wt/IM−12 (B), and GIUS 4−273 Wt/IM−13 (C), three complete shells in dorsal (A1, B1, C1), ventral (A2, B2, C2), lateral (A3, B3, C3), posterior (A4, B4, C4), and anterior (A5, B5, C5) views. D–F. Coeloterorhynchus dillanus (Schmidt, 1941), GIUS 4−273 Wt/EB−1 (D), GIUS 4−273 Wt/EB−2 (E), and GIUS 4−273 Wt/EB−6 (F), three complete shells in dorsal (D1, E1, F1), ventral (D2, E2, F2), lateral (D3, E3, F3), posterior (D4, E4, F4), and anterior (D5, E5, F5) views.