Middle Cambrian cystoid (sensu lato) stem columnals from Bornholm, Denmark |
| |
Authors: | VIVIANNE BERG-MADSEN |
| |
Institution: | Vivianne Berg-Madsen, Palaeontological Institute, Box 558, S-751 22 Uppsala, Sweden |
| |
Abstract: | A rich material of echinoderm fragments from two Middle Cambrian stratigraphical levels on Bornholm are preserved due to phosphatization of the original calcitic stereom. Preservation of echinoderms in this way - not previously recorded from the Middle Cambrian - permits detailed analysis of the three-dimensional stereom structure. Identifiable are fragments of stylophorans and eocrinoids. Stem columnals, most likely from eocrinoids, show a wide and advanced morphological variation indicating articulation similar to that of crinoids. The material from the Exsulans Limestone/Kalby marl ( Ptychagnostus gibbus Zone) represents stem-bearing cystoids older than Akadocrinus from Bohemia. The Andrarum Limestone ( Sole-nopleura brachymetopa Zone) contains echinoderm fragments from a higher stratigraphical level, a level correlatable with that from which the oldest North American stem–bearing cystoid, Eustypocystis , has been recorded. |
| |
Keywords: | Middle Cambrian Bornholm Denmark cystoids eocrinoids stylophorans stem columnals phosphatization three-dimensional stereom articulation |
|
|