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Ontogeny of the trilobite Parabolina spinulosa (Wahlenberg, 1818) from the upper Cambrian Alum Shales of Sweden

Published online by Cambridge University Press:  03 November 2011

Euan N. K. Clarkson ,
Cecilia M. Taylor  and
Per Ahlberg
Euan N. K. Clarkson
Affiliation:
Department of Geology and Geophysics, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JW, UK
Cecilia M. Taylor
Affiliation:
Department of Geology and Geophysics, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JW, UK
Per Ahlberg
Affiliation:
Department of Geology, University of Lund, Sölvegatan 13, S–223 62 LUND, Sweden
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Abstract

The ontogeny of Parabolina spinulosa is described on the basis of material from Andrarum (Skåne) and Jämtland in Sweden. Protaspides are rare, and indifferently preserved, but well-preserved isolated tagmata and complete specimens from the early meraspid stages onwards were available for study. Whereas the ontogeny is broadly similar to that of the earlier Olenus wahlenbergi, there are subtle differences, notably in a greater spinosity from the earlier stages and a gradual, rather than a sudden, change of surface sculpture in the early holaspid. P. spinulosa at all stages of growth is much more variable than is Olenus. Meraspides have larger articulating halfrings anteriorly and the first thoracic segments are of greater sagittal length than in the adult; these were adaptations which enabled Parabolina to undergo cylindrical enrollment from an early stage.

Parabolina is considered to have arisen from the earlier genus Olenus, and on the basis of comparative ontogeny many, though not all, features of Parabolina appear to be of paedomorphic origin. These include the reduction of the preglabellar field, retention of the visual surface, position of the eyes set close to the glabella, retention of a conterminant hypostome, yoking of the librigenae, spinosity of the thorax and pygidium, more numerous glabellar furrows and reduction in number of thoracic segments. Olenus attenuatus has several features intermediate between those of earlier Olenus species and Parabolina, and the origin of the latter genus is best considered in terms of a mosaic paedomorphocline.

Keywords

Cambriancuticular sculptureeyeshypostomemosaic paedomorphoclineOlenidaeontogenypygidiumSwedentrilobites
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 88 , Issue 2 , 1997 , pp. 69 - 89
Copyright
Copyright © Royal Society of Edinburgh 1997

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