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Intracolony Variation in Skeletal Growth Rates in Paleozoic Ramose Trepostome Bryozoans
Marcus M. Key, Jr.
Vol. 16, No. 4 (Autumn, 1990), pp. 483-491
Published by: Paleontological Society
Stable URL: http://www.jstor.org/stable/2400971
Page Count: 9
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All erect, branching (ramose) organisms adhere to the same fundamental geometric growth law: the rate of distal growth decreases away from the branch axis. Regardless of the phylogenetic history of an organism, the formation of cylindrical branches requires adherence to this law. In colonies coordinate the growth rates of the individual modules to produce an integrated branch? This question is addressed in the context of three Ordovician and three Devonian species of ramose trepostome bryozoans. Using remnant growing tips in the endozone as isochronous surfaces, relative rates of skeletal secretion among zooids were measured. Measurements of skeletal and void spaces across a colony branch enabled calculation of the volume of skeletal material secreted by zooids between successive remnant growing tips. Results indicate that rate of skeletal secretion systematically decreases from the branch axis outward into the exozone. This suggests that zooid morphogenesis is controlled to a certain degree by the colony. Colonial control over zooidal growth rates in turn regulates the shape of the colony.
Paleobiology © 1990 Paleontological Society