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Evolution of the embryonic development in lingulid brachiopods

100%

Balinski A.

Acta Palaeontologica Polonica

1997

tom 42

nr 1

45-56

The style of embryonic development in the lingulids has changed through time; that of Recent lingulids is not primitive for the group. The shell of Devonian lingulids consists of two valves already at the embryonic stage, whereas in Recent lingulids the protegulum originates as a single plate, subsequently folded in two. The protegulum of the Devonian lingulids is a cup-shaped, subcircular plate, usually with a characteristic radial sculpture suggesting the presence of marginal setae, similar to those occurrilg in early juvenile stages of Recent discinids. Devonian protegula are 81 to 100 µm in width and thus are three times smaller than protegula of the Recent Lingula utd Glottidia, and twice as small as those of the Late Cretaceous Lingula sp. The embryonic development of lingulids underwent important modification during last 370 Ma.

Emergence and succession of Carboniferous conodont and ammonoid communities in the Polish part of the Variscan sea

80%

Dzik J.

Acta Palaeontologica Polonica

1997

tom 42

nr 1

57-170

The end of the carbonate sedimentation of the Famennian Wocklumeria limestone in the Holy cross Mts and Sudetes coincides with the disappemance of a high-diversity warm-water assemblage of ammonoids and conodonts with elaborated platform elements. In replacement, a low diversity ammonoid community of Acutimitoceras prorsum and a thin-crown conodont Protognathodus fauna migrated to the afea. When carbonate sedimentation was re-established in the Tournaisian, the new high-diversity ammonoid and conodont faunas represented again almost the whole range of morphologies known from the Famennian. Migrations into the area from unknown sources dominated, with little contribution from the local phyletic evolution. This characteristic ammonoid-conodont community disappeared with the sea-level rise in the Siphonodella crenulata Zone, to emerge at the same time in the North American Midcontinent. The reverse direction of migrations marks the latest Tournaisian Scaliognathus anchoralis event. In yet another cycle of the late Viséan, the new high-diversity faunas were not able to develop as elaborate conch or platform element morphologies as before. In a review of the literature it is shown how the Variscan orogenic activity, progressing towards the Northeast, and glaciations in Gondwana influenced the distribution of late Carboniferous ammonoids in Poland. Conodont taxa Weyerognathus gen. n., Neopolygnathus sudeticus sp. n., and Siphonodella belkai sp. n. are proposed.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Balinski A.

1 Dzik J.

2 1997

Wyniki wyszukiwania

Evolution of the embryonic development in lingulid brachiopods

Emergence and succession of Carboniferous conodont and ammonoid communities in the Polish part of the Variscan sea