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The oldest isorophid edrioasteroid [Echinodermata] and the evolution of attachment strategies in Cambrian edrioasteroids

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Zamora S., Smith A. B.

Acta Palaeontologica Polonica

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2010

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tom 55

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nr 3

487-494

Two new middle Cambrian edrioasteroid (Echinodermata), Protorophus hispanicus gen. et sp. nov., and Isorophida gen. et sp. indet., are described from the early middle Cambrian (Cambrian Series 3, Stage 5) of Spain. These are the oldest and probably the most primitive isorophids, a clade previously known from the upper Cambrian onwards. Specimens are attached to trilobite fragments indicating that edrioasteroids had by this time separated into two lineages each with different strategies for attachment, sediment attachers and hard substrate attachers. The single U−shaped ambulacral flooring plates of Protorophus are unique while Isorophida gen. et sp. indet. shares the presence of spines in common with some pyrgocystitid isorophids. The shift from facultative soft−bottom attachment to obligate hard−ground attachment in edrioasteroids involved the retention of a juvenile trait into adulthood and was already underway by the middle Cambrian.

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Crinoid ancestry without blastozoans

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

Acta Palaeontologica Polonica

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2016

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tom 61

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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.

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Morphology and ontogeny of the Cambrian edrioasteroid echinoderm Cambraster cannati from western Gondwana

80%

Zamora S., Sumrall C. D., Vizcaino D.

Acta Palaeontologica Polonica

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2013

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tom 58

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nr 3

A review of the Cambrian edrioasteroid echinoderm Cambraster cannati is made based on new collections from the Iberian Chains (NE Spain) and Montagne Noire (France). New morphological data include a completely articulated oral area and details of ambulacra. Specimens ranging from 4 to 26 mm in diameter provide detailed information concerning the full ontogeny. Important changes through ontogeny mainly affect the marginal ring and the plating pattern of the aboral surface. Comparison with other species of Cambrasterindicates that the aboral surface of Cambraster tastudorum from Australia shows strong resemblance to juvenile specimens of C. cannati. Cambraster cannati was attached directly to the substrate and inhabited relatively high energy, offshore environments from the west margin of Gondwana. Abnormalities in the skeleton are described for the first time in a Cambrian edrioasteroid.

Ograniczanie wyników

3 Acta Palaeontologica Polonica

2 Zamora S.

1 Blake D. B.

1 Guensburg T. E.

1 Mooi R.

1 Smith A. B.

1 Sprinkle J.

1 Sumrall C. D.

1 Vizcaino D.

1 2016

1 2013

1 2010

The oldest isorophid edrioasteroid [Echinodermata] and the evolution of attachment strategies in Cambrian edrioasteroids

Crinoid ancestry without blastozoans

Morphology and ontogeny of the Cambrian edrioasteroid echinoderm Cambraster cannati from western Gondwana