Flabellulirostrum rackii, Baliński, 2006

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 : 660-662

Flabellulirostrum rackii sp. nov.

Figs. 8E–G , 11 , 12 .

Holotype: Complete shell ZPAL Bp 60/12 ( Fig. 8G ).

Type horizon: Complex C, bed 44, Palmatolepis transitans conodont Zone.

Type locality: Wietrznia Ie quarry, SE part of city of Kielce; GPS coordinates: N 50°51’21.0’’, E 20°38’30.6’’.

Derivation of the name: In honour of Professor Grzegorz Racki, in recognition of his contribution to the knowledge of geology and Devonian brachiopods of the Holy Cross Mountains.

Diagnosis.—Shell up to 17.1 mm in length, widely elliptical in outline, widest at about midlength, with long cardinal margin, flat to more often concave ventral flanks in anterior view, with 5–9 costae; sulcus wide, with slightly convex bottom, widening rapidly anteriorly; fold with flat to slightly convex top and 5–9 (mean 6) costae. Differs from other species of the genus by having wider shell. From close F. kielcensis sp. nov. it differs by having flat to concave flanks and sharp−edged lateral commissure.

Material.—Thirty nine complete shells and 42 fragments of shells and single valves from Wietrznia Id−W (beds 4, 14, and 18) and Ie sections (beds 43–45 and 48). The species is most numerous in bed 18 of Wietrznia Id−W and beds 44–45 of the Wietrznia Ie sections (Figs. 2, 3).

Description.—Shell medium sized for genus, dorsibiconvex, widely elliptical in outline with the greatest width at about midlength. The cardinal margin broadly obtuse, lateral margins rounded, lateral commissure sharp−edged, anterior margin truncated, anterior commissure strongly uniplicate.

Ventral valve gently convex in lateral profile, beak erect to slightly incurved; flanks sloping gently from the umbonal region, flat to more often concave in anterior view; sulcus wide, originating about 6–7 mm anterior to beak, with slightly convex bottom, widening rapidly and forming long, wide, distally slightly rounded tongue; sulcus bounded clearly from flanks, anteriorly the bounding area projects often forming spur−like extensions.

Dorsal valve moderately convex in lateral profile, sometimes with flattened anterior; regularly domed in anterior view; fold originating about the midvalve, with slightly convex to almost flat top.

Shell without costae in posterior half but covered by fine, flat, radiating capillae (about 4–8 per mm); anterior surface without capillae but costate, costae strong, separated by narrow interspaces, generally with rounded top, sometimes median costae become higher and acute at the commissure; costae simple, divisions or intercalations not observed, flanks marked by 5–9 costae, fold with 5–9 (mean 6; Fig. 12 ), and sulcus with 4–8 costae; parietal costae usually absent, exceptionally up to two obscure costae may be traced with difficulties. On several shells median costae are wider and stronger than lateral ones.

Interior of ventral valve ( Fig. 11 ) without dental plates, with thickened umbonal region. Dorsal valve interior ( Fig. 11 ) with high, strong median septum supporting short, horizontal hinge plates; cardinal process large, wide, with distinct longitudinal crenulation; crura closely set, short, with ventrally curved tips.

Remarks.—This species occurs in the same beds together with a larger phenotype of Flabellulirostrum kielcensis sp. nov. For the first glance both forms seem to be conspecific but detailed study revealed that there are important differences between them. The most important and consistent difference is in the shape of ventral flanks which in F. rackii are flat to more often concave, whereas in F. kielcensis sp. nov. they are convex. They differ also in the shape of lateral commissure which is sharp−edged in the former but blunt, more round−edged in the latter. The bottom of the tongue is flat to convex in F. rackii but flat to concave in F. kielcensis .)

mm

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Thickness

Length (mm) Width (mm)

The former species differs also in its slightly wider outline and in having very distinct, spur−like lateral borders of the ventral sulcus, which in the latter is rounded and less conspicuous. Occurrence.—The species occurs in the Wietrznia Id−W and

Wietrznia Ie sections; these represent Palmatolepis transitans conodont Zone.

Figures

Fig. 8. Rhynchonellid brachiopods from the Frasnian of Wietrznia and Dębnik. A. Flabellulirostrum guerichi (Baliński, 1979), ZPAL Bp 60/15, complete shell from the Nodular Limestone (Palmatolepis hassi Zone) of Dębnik in dorsal (A1), ventral (A2), lateral (A3), posterior (A4), and anterior (A5) views. B–D. Flabellulirostrum kielcensis sp. nov., ZPAL Bp 60/1 (B), ZPAL Bp 60/2 (C), and GIUS 4−273 Wt/IM−1 (D), three shells (C—holotype) from the middle Wietrznia Beds of Wietrznia Ie (B, C) and Id−W (D), in dorsal (B1, C1, D1), ventral (B2, C2, D2), lateral (B3, C3, D3), posterior (B4, C4, D4), and anterior (B5, C5, D5) views. E–G. Flabellulirostrum rackii sp. nov., ZPAL Bp 60/11 (E), GIUS 4−273 Wt/IM−9 (F), and ZPAL Bp 60/12 (G), three shells (G—holotype) from the middle Wietrznia Beds of Wietrznia Ie (E, G) and Id−W (F) in dorsal (E1, F1, G1) ventral (E2, F2, G2), lateral (E3, F3, G3), posterior (E4, F4, G4), and anterior (E5, F5, G5) views.

Fig. 11. Serial sections of two shells of Flabellulirostrum rackii sp. nov., ZPAL Bp 60/30 (A) and ZPAL Bp 60/31 (B), middle Wietrznia Beds of Wietrznia Ie. Numbers refer to distance in mm from ventral umbo.

Fig. 12. Scatter diagrams of shell width to shell length (A), shell thickness to shell length (B), sulcus width to shell width (C), and number of costae on fold to shell width (D) ratios in Flabellulirostrum rackii sp. nov. from Wietrznia.