Chimaerothyris dombrowiensis (Gurich) Z dolnego eiflu Gór Świętokrzyskich

Abstract

Przedstawiono wyniki rewizji paleontologicznej ramienionoga "Spirifer" dombrowiensis Gürich z obszaru Gór Świętokrzyskich. Wyznaczono neotyp badanego gatunku i stwierdzono jego przynależność do rodzaju Chimaerothyris. W zasięgu występowania tego taksonu uzasadniono wydzielenie w dolnym eiflu Gór Świętokrzyskich nie powiązanej samoistnej jednostki biostratygraficznej -poziomu Chimaerothyris dombrowiensis.CHIMAEROTHYRIS DOMBROWIENSIS (GÜRICH) FROM THE LOWER EIFELIAN IN THE GÓRY ŚWIĘTOKRZYSKIE MTS The paper presents the results of analysis of Devonian brachiopod know in the literature as “Spirifer” dombrowiensis Gürich, 1896. In Poland, it is known from the Góry Świętokrzyskic Mts only but it has been shown to be important for local stratigraphic correlations (G. Gürich, 1896; D. Sobolev, 1909; J. Czarnocki. 1951; M. Pajchlowa, 1957). However, uncertian generic status and imprecise definition of the type locality made necessary paleontological revision of this taxon. My studies on material from well-known outcrops of the Eifelian (Dąbrowa, Grzegorzowice, Brzeziny, Łabędziów and Zbrza) and borehole columns Kolejówka IG 1. Kostomłoty IG 1, Strawczynek IG 1, Porzecze IG 5a and Stara Góra IG 1 (Fig. 1) showed that morphological features and internal structure make possible assignation of this species to the genus Chimaerothyris Paulus, Struve et Wolfart, 1963. The specimens described by G. Gürich (1896) have been lost 50 neotype is designated here (Table 1. Fig. 1a -c). Paleontological description Spiriferida Waagen, 1883 Family Spinocyrtiidae Ivanova, 1959 Genus Chimaerothyris Pauius, Struve et Wolfart, 1963 Chimaerothyris dombrowiensis (Gürich). 1896 N e o t y p e (Table 1, Fig. 1a-c); specimen no. OS-162/1 ; Zbrza locality, the Góry Świętokrzyskie Mts. D i m e n s i o n s  of n e o t y p e  (in mm): Shell: maximum width - 45, height - 30, length of ventral valve – 35, length of dorsal valve – 25, maximum width of sulcus - 13, angle of inclination of area in ventral valve - 135°, angle of opening of sulcus - 26°. number of costae - 26. D i a g n o s I s. Shell biconvex, pentagonal to rhomboidal in outline, the widest in hinge line throughout the development. Hinge extremities more or less elongate: posterior margin folded. of the uniplicate type; surface of valves covered with coarse costae; sulcus and fold smooth. M a t e r i a!. About 15O specimens, housed in the Museum of the Świętokrzyski Branch of the Geological Institute. Kielce (colI. no. OS-162(1-24). D e s c r i p t i o n. Ventral valve strongly convex, umbo bent, area straight to weakly concave, covered with distinct growth lines; delthyrium large, triangular, deltidial plates missing. Posterior margin once folded. elongate, linguiform in the middle; sulcus wide, V-shaped in cross-section. Dorsal valve less convex, equal a half to two-thirds of the ventral at the average, with strongly bent umbo. Area low, hinge straight. fold triangular in outline, somewhat rounded. Ornamentation consisting of high coarse costae with rounded to somewhat flattened crests, spreading from the beak; costae varying in width but the thickest close to valve margin, 8 - 10 in number in juvenile forms and 12 - 14 at each side of sulcUli or fold in mature ones. Surface of sulcus and fold smooth, except for concentric growth lines. present throughout the valve and most closely spaced near its margins. Microornamentation comprising concentric elements - rugellae (B. Paulus, W. Struve, R. Wolfart, 1963), best visible on upper surface of costae (about 10 per 1 mm) and radial ones - radioli (op. cit.), weakly visible in this species. Delthyrium completely open in apical cavity of ventral valve; both deltidial and delthyrial plates lacking. Delthyrial space may be narrowed by secondary thickenings at sides of dental plates, forming so-called false delthyrial plate (E.A. Ivanova, 1971). Dental plates well developed. crural base; well marked; brachidium complex, in the form of two conical spires. O c c u r r e n c c e: Poland, the Góry Świętokrzyskie Mts - Lower Eifelian. The stratigraphic position of this species was tentatively precised on the basis of records of conodonts of the group Icriodus corniger Wittekindt. A unconnected biostratigraphic unit - the Chimaerothyris dombrowiensis zone - is proposed for the range of occurrence of this taxon in the Lower Eifelian of the Góry Świętokrzyskie Mts.