Vol 56, No 1-2 (2022)

Authors: Michal Mergl

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 Abstract: The earliest known Cyrtina in the Prague Basin has been discovered in the Kotýs Limestone of the Lochkov Formation (Lochkovian) among a rich brachiopod-coral fauna at Branžovy ridge near Bubovice (Beroun District, Czechia). Rare and imperfectly preserved silicified shells are assigned to Cyrtina praecedens Kozłovski, 1929, a species originally described from Podolia, Ukraine. The species is known also in north-eastern Russia (Tajmyr and Sette-Daban Mts) and likely also in New South Wales, Australia. Its distribution provides evidence of the rapid spread of Cyrtina across the shallow shelves of Laurussia, Siberia and Gondwana in the Early Devonian. The Devonian and Carboniferous distribution of Cyrtina is restricted to the agitated, shallow-water carbonate environment in tropical and temperate climatic belts.

Authors: Jiří Bek & Kishore Goswami

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 Abstract: The extant plant genus Isoetes (Isoetaceae; lycophyte, quillwort) is important from an evolutionary point of view. Species of this heterosporous genus are small herbs (up to 50 cm) and exhibit some morphological, anatomical and embryological features of their Paleozoic arborescent lycopsid ancestors. The species Isoetes pantii produces three kinds of microspores (monolete, alete and trilete) and two types of trilete megaspores in one and the same heterosporangium. We attempt to associate these unusual functional megaspores with various Paleozoic spores described mainly from Devonian barinophytaleans such as Omniastrobus dawsonii, Barinophyton richardsonii, B. citrulliforme and Protobarinophyton pennsylvanicum. These have two kinds of spores in a sporangium and provide the first palynological evidence of heterospory at 405 Ma. The germination of microspores and megaspores and production of gametophytes within the heterosporangia of I. pantii corresponds with that of some of its Paleozoic ancestors. Retention of megaspores within heterosporangia and their germination in situ offers evidence that I. Pantii exhibits the probable route of evolution of the seed habit. These observations support the hypothesis that a typical heterosporangium was the cradle for the evolution of heterospory.

Authors: Michal Mergl & Nikola Šmídtová

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 Abstract: Diminutive crinoid holdfasts and cemented tests of the foraminifers Psammosphaera and Tolypammina were observed on coarse bioclasts in weathered limestones of the Daleje-Třebotov Formation. Specimens were obtained in 1984 by washing so called “white beds” at a temporary locality in Praha-Barrandov. A few millimeter sized bioclasts with epibionts were freed from hard limestone beds of the Třebotov Limestone near the Lower/Middle Devonian boundary by long-term weathering. Many of the crinoid holdfasts attached to pluricolumnals provoked a stereomic response of the host crinoid. Also the growth orientation of the crinoid epibiont is not random and indicates some crinoid-epibiont to crinoidhost interaction. Reaction of host stereome and non-random stem orientation offer direct evidence of epibiont larval settlement and subsequent growth on the stem of a living crinoid host. The extensive growth of the host stereome ended by partial to total engulfing of the epibiont holdfast. This indicates advancing and finally successful defence of the host crinoid against the epibiont. The holdfast gives evidence that the small host crinoids offered a somewhat higher tier for even smaller epibiont crinoids. However, other observed holdfasts indicate fixation of larva and growth over loose bioclasts lying on a sea bed. Location of foraminifer test on bioclasts confims that foraminifers cemented and grew on loose echinodermal and brachiopod remains and preferred crevices and similar protected sites with concave profiles. This is clear evidence that diverse bioclasts (brachiopod shells, pelmatozoan ossicles) provided the hard substrate suitable for epibiont life on a sea bed.

Authors: Erwin L. Zodrow & Josef Pšenička

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 Abstract: Reported are descriptions of twelve samples representing a variety of sideritic structures, including nodules mostly from roof shale of the Middle Pennsylvanian Sydney Coalfield, Canada. The co-occurrence of fossiliferous nodules and compression fossils in the shaley roof rocks at Point Aconi enhance greatly palaeontological information. Newly discovered in a coal seam, and part of the sample, is a 40 mm thick continuous sheet-like layer of siderite with abundant permineralized-like-compressed small to micron-sized structures in a rather evenly-sized sideritic matrix, probably indicating a genetic origin different from that of the nodules. Methods include some thin-section, and two X-Ray analysis. However, large systematic sampling is a prerequisite to explore that situation, which additionally could provide faunal information for Euromerican correlation.

Authors: František Hartl, Václav Vokáč, Miroslav Pavlovič, Tomáš Mrázek & Martin Šafka

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 Abstract: The deep-water Aulacopleura koninckii Assemblage in the lower Homerian (T. testis Sub-Biozone) “Aulacopleura shales“ strata at the classical ‘Barrande's pits’ locality on the Černidla hillside at Loděnice in the Prague Basin is supplemented by the addition of two new trilobite taxa, viz. Exallaspis? perunicana sp. n. and Kosovoproetus? aff. praecursor (Přibyl & Vaněk 1987). The palaeogeographic distribution of Exallapis Ramsköld & Chatterton, 1991 is extended by the occurrence of Exallaspis? perunicana sp. n. and the younger Exallaspis sp. in the upper Homerian (the P. parvus – G. nassa Biozone) of the Prague Basin, reflecting the faunal migration between the southern shelf of the Baltica palaeocontinent and the Perunica microcontinent accross the Rheic Ocean. The small dimensions of the K.? aff. praecursor exoskeletons compared to those of K.? praecursor in the bordering shallow-water Liolalax–Sphaerexochus–Cheirurus Assemblage represent another example of adaptive nanism in trilobites of the Aulacopleura-Raphiophorus Biofacies.