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Comparative Ecology of Bryozoan Radiations: Origin of Novelties in Cyclostomes and Cheilostomes

David Jablonski, Scott Lidgard and Paul D. Taylor
PALAIOS
Vol. 12, No. 6 (Dec., 1997), pp. 505-523
DOI: 10.2307/3515408
Stable URL: http://www.jstor.org/stable/3515408
Page Count: 19
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Comparative Ecology of Bryozoan Radiations: Origin of Novelties in Cyclostomes and Cheilostomes
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Abstract

Cyclostome and cheilostome bryozoans diversified at different times and consequently in different ecological contexts. Cyclostomes began their rebound from a Permo-Triassic bottleneck in the early Jurassic, prior to increases in bioturbation, durophagous predation, and other ecological changes of the Mesozoic Marine Revolution. Cheilostomes did not appear until the latest Jurassic and rapid diversification began only in the mid-Cretaceous, when the Mesozoic Revolution was well under way. We compare the radiations of these two groups to test for similarities in the within-group patterns of origin of biologically significant novelties, and for between-group differences that might be due to ecological context or group attributes. As seen for other invertebrate taxa, within-group novelties were not concentrated in onshore settings, in contrast to origination patterns at the ordinal level. Differences in environment of first occurrence and rapidity of novelty acquisition were not obviously related to the Mesozoic Revolution, or to the distinction between zooid- and colony-level characters. The contrast in novelty acquisition rates may partly reflect group-specific constraints. In cyclostomes, novelties appeared rather evenly over 100 Ma, whereas in cheilostomes many of the novelties appeared in the Late Albian-Early Cenomanian during a period of rapid diversification. Despite a slow start (Late Jurassic-mid Cretaceous), the cheilostome radiation entered an explosive phase that may characterize successful establishment of groups founded late in the Phanerozoic.

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