Gothograptus aff. domeyki KOZŁOWSKA , BATES, ZALASIEWICZ et RADZEVIČIUS, 2019

Štorch, Petr & Manda, Štěpán, 2019, Little Known Homerian (Lower Silurian) Graptolites From Kosov Quarry Near Beroun, The Czech Republic, Fossil Imprint 75 (1), pp. 44-58 : 48

Gothograptus aff. domeyki KOZŁOWSKA, BATES, ZALASIEWICZ et RADZEVIČIUS, 2019

Text-fig. 4 a–c

1952 Gothograptus nassa ( HOLM, 1890); Bouček and Münch, pp. 11–15, fig. 2a–i, (non 3a–d), pl. 1, figs 9–11.

aff. 2019 Gothograptus domeyki n. sp.; Kozłowska et al., figs 7g, 10b.

M a t e r i a l. More than one hundred flattened, more or less complete rhabdosomes from the upper lundgreni Biozone of the Kosov 2 section (samples K2/23–K2/11; see Manda et al. 2019: fig. 2).

D e s c r i p t i o n. Mature, up to 11.8 mm long rhabdosome has 10–12 pairs of thecae and well-developed appendix. The rhabdosome is 1.05–1.22 mm wide (M = 1.1 mm, n = 14) in its parallel-sided proximal and mesial part, then slowly tapers to 0.35–0.43 mm just below the appendix. 2TRD increases from 1.54–1.6 mm at th2 (M = 1.56 mm, n = 12) to 1.7–1.75 mm (M = 1.73, n = 14) in th5–6. Small but distinct genicular hoods of nassa - type are developed on the first and, in some specimens also second ( Text-fig. 4a ) pair of thecae. The next pair of thecae possesses small, laterally situated spines. Subsequent thecal orifices lack any genicular processes. The orifices are rather narrow, broadly sub- rectangular or somewhat pyramidal, with markedly thickened apertural lips ( Text-fig. 4b ). Mature specimens have a dense reticulum of similar thickness to the clathrial framework.

R e m a r k s. The present gothograptid form differs from Gothograptus domeyki KOZŁOWSKA et al., 2019 in having markedly longer finite rhabdosome, with up to 12 pairs of thecae, more widely spaced thecae and small genicular hoods developed on first, and rarely, second pair of thecae. Other characters, such as the absence of any apertural/genicular processes on most thecae and thickened apertural lips are shared with G. domeyki , which is known to date solely from the upper lundgreni Biozone of Lithuania ( Kozłowska et al. 2019). Also specimens described by Bouček and Münch (1952) from the lundgreni Biozone of Bykoš and Borek localities and assigned to Gothograptus nassa ( HOLM, 1890) belong to this form. All figured specimens represent mature rhabdosomes, up to 13 mm long, 1.0– 1.2 mm wide, with up to 12 pairs of thecae. Thecal orifices are narrow, broadly pyramidal, with thickened lips, small lateral spines in some proximal thecae but generally lacking nassa - type hoods. Well-developed appendix and dense reticulum are consistent with full maturity of the colonies.

Abundant occurrence of two early gothograptids of Baltic provenance in the upper lundgreni graptolite Biozone of the Prague Synform is in full compliance with close links between Homerian graptolite faunas of peri-Gondwanan Europe (namely of Perunica microplate) and Baltica.

Figures

Text-fig. 4. Retiolitid graptolites from the upper lundgreni Biozone of the Kosov section. a–c – Gothograptus aff. domeyki KOZŁOWSKA et al., 2019: a – PŠ 3869, finite rhabdosome in profile with small nassa-type genicular hoods on 1st and 2nd pair of thecae, sample K2/18; b – PŠ 3905, specimen in latero-ventral view showing narrow orifices, thickened thecal lips and very small genicular hood on th 1, sample K2/22; c – PŠ 3877b, specimen in obverse view with small genicular hoods on th11 and th12, and small lateral spines in the next two thecae, sample K2/15. d–f – Gothograptus kozlowskii KOZŁOWSKA-DAWIDZIUK, 1990: d – PŠ 3878, specimen showing broadened bases of the apertural spines, sample K2/11; e – PŠ 3870, finite rhabdosome in obverse profile view, sample K2/13; f – PŠ 3868, latero-ventral (subscalariform) view, sample K2/21. g – Semigothograptus meganassa (RICKARDS et PALMER, 2002): PŠ 3863, sample K2/6. All specimens × 10, scale bar 1 mm.