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Crinoid ancestry without blastozoans

100%

Guensburg T. E., Blake D. B., Sprinkle J., Mooi R.

Acta Palaeontologica Polonica

2016

tom 61

nr 2

At present, a debate in the paleontologic literature focuses on whether or not the immediate ancestry of the Crinoidea lies in an unidentified member of the Blastozoa, which includes eocrinoids and an assemblage known variously as the “cystoids”. Those proposing to derive crinoids from within the blastozoans have recently argued for homologies in the construction of the oral region of certain derived taxa from both groups. An opposing viewpoint, outlined here, finds evidence that aside from plesiomorphies, proposed similarities are superficial and homoplastic. We suggest these superficialities represent convergent adaptive strategies. Earliest crinoids express ambulacral traits unlike any blastozoan but that are expressed in the only other pentaradial echinoderms with a known record early enough to be considered in the context of crinoid origins, edrioasteroids and edrioasteroid-like stem echinoderms.

A new pleurocystitid blastozoan from the Middle Devonian of the Eifel (Germany) and its phylogenetic importance

80%

Nardin E., Bohaty J.

Acta Palaeontologica Polonica

2013

tom 58

nr 3

Rich echinoderm fauna from the Middle Devonian of the Eifel (Rhenish Massif, Germany) has yielded specimens of the rare recumbent pleurocystitid rhombiferans. Regulaecystis testudineus sp. nov. extends the stratigraphic range of the pleurocystitids to the Eifelian (Middle Devonian). Specimens show a strongly inflated and ornamented theca, which is unusual for the European pleurocystitids. Phylogenetic analysis of all described pleurocystitid genera suggests a close relationship of Regulaecystis with the other Devonian genera. Results indicate that the degree of inflation and of ornamentation of the theca can be interpreted as convergences within the pleurocystitids due to environmental conditions (such as surface consistency, hydrodynamism). R. testudineus sp. nov. was living as a strict epibenthic vagile organism; lying on muddy soft to firm substrates in quiet to agitated shallow warm water environments.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Blake D. B.

1 Bohaty J.

1 Guensburg T. E.

1 Mooi R.

1 Nardin E.

1 Sprinkle J.

1 2016

1 2013

Wyniki wyszukiwania

Crinoid ancestry without blastozoans

A new pleurocystitid blastozoan from the Middle Devonian of the Eifel (Germany) and its phylogenetic importance