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Astogenetic and Environmental Variation of Zooid Size within Colonies of Jurassic Stomatopora (Bryozoa, Cyclostomata)

Paul D. Taylor and Robert W. Furness
Journal of Paleontology
Vol. 52, No. 5 (Sep., 1978), pp. 1093-1102
Stable URL: http://www.jstor.org/stable/1303855
Page Count: 10
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Astogenetic and Environmental Variation of Zooid Size within Colonies of Jurassic Stomatopora (Bryozoa, Cyclostomata)
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Abstract

Zooid size variation was examined in four colonies of Stomatopora bajocensis and three of S. dichotomoides, and related to astogeny (colony development) and environmental factors. Two astogenetic zones may be distinguished; an initial one of increasing zooid size, followed by one of constant mean zooid size. The boundary between these zones was objectively determined by a regression method. Although variable between characters and between colonies, this statistic showed consistent differences between the two species, and thus may be of taxonomic value. Temporal environmental variation was shown to be small, while spatial heterogeneity predominated, and was examined in detail in one colony using a novel statistical technique. Three possible reasons for the budding of small zooids during early astogeny are suggested; rapid commencement of feeding by the colony, enhanced filter feeding efficiency, and avoidance of competition with established colonies.

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