Sphenospira julii ( Dehée, 1929 )

Halamski, Adam T. & Baliński, Andrzej, 2009, Latest Famennian brachiopods from Kowala, Holy Cross Mountains, Poland, Acta Palaeontologica Polonica 54 (2), pp. 289-306 : 300-302

Sphenospira julii ( Dehée, 1929)

Figs. 8 , 9H–K.

1929 Spirifer Julii nom. nov.; Dehée 1929: 19–21, pl. 2: 1–8.

1969 Sphenospira julii (Dehée) ; Kaliś 1969: 812, pl. 2: 3.

1976 Sphenospira julii (Dehée) ; Matyja 1976: 504, 509, pl. 14: 1, 2, 4, 5.

non 1987 Sphenospira julii ( Dehée, 1929) ; Jendryka−Fuglewicz and Fuglewicz 1987: 87–88, pls 1, 2.

?1995 Sphenospira ? sp.; Baliński 1995: 75–77, pl. 15: 3–5, fig. 22.

Material.—15 shells, most often preserved only fragmentarily, ZPAL Bp 57/9, 11–16, 19, 23, 91–96, 114.

Description.—Shell large (up to 56 mm wide), transverse, strongly ventribiconvex. Ventral valve subconical. Maximal width at cardinal margin. Dorsal fold distinct, semi−ovate in transverse section, relatively narrow (up to one fourth of the shell width). Ventral sulcus distinct, U−shaped in transverse section, moderately deep. Anterior commissure uniplicate to paraplicate. Ventral interarea apsacline to procline (in older shells), very high (height to width ratio 0.43–0.52), sometimes concave, longitudinally striate. Deltidium occupying one fifth to one fourth of the interarea; delthyrial plate, with median longitudinal, rounded ridge, visible in one specimen ( Fig. 8J 3). Dorsal interarea catacline, linear.

Ornamentation of strong radial costae, separated by narrower furrows, in the largest two specimens 13 in the fold, 15 in the sulcus, and 19?–24 on lateral flanks.

Interior unknown.

Remarks.—The material reported under this name by the present authors consists mostly of smaller specimens than the major part of the type collection of the species from Étroeungt ( Dehée 1929): the largest specimen from Kowala (ZPAL Bp 57/91, Fig. 9K) is 56 mm wide, whereas in the French ones a width of ca. 60–80 mm is rather a rule than an exception. Moreover, the discussed material is quite diversified in the density of costation: in the median region of the dorsal valve (near the fold) from 3 costae per 5 mm (ZPAL Bp 57/14) to 4 per 5 mm (ZPAL Bp 57/96); in the median region of the ventral valve (near the sinus) from 3.5 per 5 mm (ZPAL Bp 57/96) to 4.5 per 5 mm (ZPAL Bp 57/9; 11 per 5 mm in the lateral region). A similar phenomenon occurs in the type collection from Étroeungt: for example, the holotype MGL 1582 has about 3 costae per 5 mm in the median region of the dorsal valve, and 5 costae per 5 mm in the lateral regions thereof, whereas the corresponding values for the ventral valve are, respectively, 4 and 9, whereas the dorsal valves MGL 1581 and MGL 1579 ( Dehée 1929: pl. 8: 4 and 2, respectively) show the following pairs of values: 1.5 and 4, 3.5 and 10 ( Dehée 1929; Nicollin 2004). In both collections therefore, the variation is strong, but ventral valves are usually more finely costate than dorsal ones. Poor stratigraphic resolution of the type collection and lack of better material in the type locality ( Nicollin 2008) hampers recognition of the above−mentioned morphotypes from the type area as representing intraspecific variability or being consecutive stages of a chronophyletic evolution. The first possibility was preferred and a wide understanding of the discussed taxon is admitted.

In Poland, this species was reported from Pomerania by Matyja (1976) and from the Lublin Basin by Kaliś (1969). A similar form (poorly preserved, described as Sphenospira sp. ) was found by Baliński (1995) in approximately coeval strata of the Dębnik Anticline.

The spiriferid described as Sphenospira julii ( Dehée, 1929) by Jendryka−Fuglewicz and Fuglewicz (1987) from exotic material of Kruhel Wielki (Carpathians, southern Poland) differs from S. julii in having curved hinge margin (straight in the latter), very faint costation (strong in S. julii ), and less distinct sinus and fold. In consequence, the form from Kruhel Wielki represents most probably another species. The age determination of the brachiopod−bearing level by Jendryka−Fuglewicz and Fuglewicz (1987), based primarily on stratigraphic occurrence of S. julii may therefore be considered as unwarranted.

Stratigraphic and geographic distribution.—Dinant Synclinorium ( Belgium), Avesnois ( France), Velbert Anticline ( Germany), Holy Cross Mts., Pomerania, Lublin Basin ( Poland), Dniepr−Donets Trough, Kuznetsk Basin, Ural ( Russia), Transcaucasia, Mongolia ( Nicollin and Brice 2004: 440; present study). Famennian, in all cases where satisfactory stratigraphic precision is available the age of beds with S. julii is latest Famennian (Strunian).

Figures

Fig. 8. Biometrical characteristics of Novaplatirostrum sauerlandense Sartenaer, 1997 from the type section (after Sartenaer 1997) and from Kowala. A. Comparison of the shell outline of representatives of the two collections on a width to length scatter diagram. B. Comparison of costation of the two collections.