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Larval Adaptations and Patterns of Brachiopod Diversity in Space and Time

James W. Valentine and David Jablonski
Evolution
Vol. 37, No. 5 (Sep., 1983), pp. 1052-1061
DOI: 10.2307/2408418
Stable URL: http://www.jstor.org/stable/2408418
Page Count: 10
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Larval Adaptations and Patterns of Brachiopod Diversity in Space and Time
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Abstract

Modern biodistributional patterns suggest that modes of larval development are a factor in determining the patterns of diversity of benthic invertebrates. Taxa restricted to a single larval mode tend to have restricted distribution patterns. While it is possible that the articulates have always been nonplanktotrophic, Paleozoic brachiopods had diversity patterns suggesting that they possessed both planktotrophic and nonplanktotrophic modes; they dominated the skeletonized faunas in many tropical benthic communities. We suggest that the planktotrophic lineages were lost to extinction, probably mostly or entirely during the Permian-Triassic event, and that the failure of the articulate brachiopods to regain their former importance owes significantly to restrictions arising from their nonplanktotrophic developmental mode. The effects of developmental modes may well be important in the evolutionary history of many taxa. The crinoids (Strathmann, 1978a) may represent another taxon restricted to nonplanktotrophy by extinction of planktotrophic lineages. By contrast, bivalves, neogastropods, and echinoids are groups with both planktotrophic and nonplanktotrophic species and they have particularly flourished during the Cenozoic. Thus important elements of the post-Cambrian Paleozoic benthic fauna (Fig. 1) may have lost the planktotrophic developmental mode during Permian-Triassic extinctions, and partly for this reason lost their dominance in post-Paleozoic times to higher taxa that retained or recaptured their developmental flexibility.

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