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Volumn 281, Issue 5378, 1998, Pages 807-809

Decoupled temporal patterns of evolution and ecology in two post- paleozoic clades

Author keywords

[No Author keywords available]

Indexed keywords

CENOZOIC; ECOLOGY; EVOLUTION; MESOZOIC; PALEOECOLOGY; TEMPORAL VARIATION;

EID: 0032493896     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.281.5378.807     Document Type: Article
Times cited : (76)

References (48)
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    • All bryozoan fragments retained on 0.5-mm and larger screens were picked from 60 entire disaggregated 0.3-to 3.0-kg samples or, where bryozoans were extraordinarily abundant, from subsamples; fragments were sorted on the basis of clade, and total mass for each clade was determined directly or calculated on the basis of subsamples. Species that produce colony fragments typically smaller than 0.5 mm have not been included in most previous studies of bryozoan species diversity [summarized in (13)]. We have excluded such small size fragments from our calculations of relative skeletal mass as well; these fractions are subject to winnowing in many recent bryozoan habitats and are rarely derived from the ecologically dominant taxa. Nonetheless, small colonies of cyclostomes and cheilostomes may be numerous in some environments (E. Håkansson, personal communication). Our data were supplemented by data in O. Berthelsen, Danmarks Geol. Unders. 83, 1 (1962) and A. H. Cheetham, Smithsonian Contrib. Paleobiol. 6, 1 (1971). Some variation in the data inevitably results from variable amounts of cement or of matrix or shell fragments. Cyclostomes tend to have thinner walls than do cheilostomes, and raw cheilostome mass was weighted by 1.26 on the basis of a thin-section determination of the ratio of skeleton to cement plus adherent material in control samples [33 cheilostomes (X̄ = 0.62, SD = 0.147) and 35 cyclostomes (X̄ = 0.51, SD = 0.151) from four representative collections]. Additional "noise" in the data may be due to different taphonomic responses of cyclostome and cheilostome bryozoans in different environments. However, dissolution and abrasion rates of mineralized bryozoans are dependent upon diverse factors that cut across clade assignment [A. M. Smith, C. S. Nelson, P. J. Danaher, Palaeogeogr. Palaeoclimatol. Palaeoecol. 93, 213 (1992); A. M. Smith and C. S. Nelson, in Biology and Palaeobiology of Bryozoans, P. J. Hayward, J. S. Ryland, P. D. Taylor, Eds. (Olsen & Olsen, Fredensborg, Denmark, 1994), pp. 177-180; in Bryozoans in Space and Time, D. P. Gordon, A. M. Smith, J. A. Grant-Mackie, Eds. (National Institute of Water & Atmospheric Research Ltd., Wellington, New Zealand, 1996), pp. 213-226.
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    • All bryozoan fragments retained on 0.5-mm and larger screens were picked from 60 entire disaggregated 0.3-to 3.0-kg samples or, where bryozoans were extraordinarily abundant, from subsamples; fragments were sorted on the basis of clade, and total mass for each clade was determined directly or calculated on the basis of subsamples. Species that produce colony fragments typically smaller than 0.5 mm have not been included in most previous studies of bryozoan species diversity [summarized in (13)]. We have excluded such small size fragments from our calculations of relative skeletal mass as well; these fractions are subject to winnowing in many recent bryozoan habitats and are rarely derived from the ecologically dominant taxa. Nonetheless, small colonies of cyclostomes and cheilostomes may be numerous in some environments (E. Håkansson, personal communication). Our data were supplemented by data in O. Berthelsen, Danmarks Geol. Unders. 83, 1 (1962) and A. H. Cheetham, Smithsonian Contrib. Paleobiol. 6, 1 (1971). Some variation in the data inevitably results from variable amounts of cement or of matrix or shell fragments. Cyclostomes tend to have thinner walls than do cheilostomes, and raw cheilostome mass was weighted by 1.26 on the basis of a thin-section determination of the ratio of skeleton to cement plus adherent material in control samples [33 cheilostomes (X̄ = 0.62, SD = 0.147) and 35 cyclostomes (X̄ = 0.51, SD = 0.151) from four representative collections]. Additional "noise" in the data may be due to different taphonomic responses of cyclostome and cheilostome bryozoans in different environments. However, dissolution and abrasion rates of mineralized bryozoans are dependent upon diverse factors that cut across clade assignment [A. M. Smith, C. S. Nelson, P. J. Danaher, Palaeogeogr. Palaeoclimatol. Palaeoecol. 93, 213 (1992); A. M. Smith and C. S. Nelson, in Biology and Palaeobiology of Bryozoans, P. J. Hayward, J. S. Ryland, P. D. Taylor, Eds. (Olsen & Olsen, Fredensborg, Denmark, 1994), pp. 177-180; in Bryozoans in Space and Time, D. P. Gordon, A. M. Smith, J. A. Grant-Mackie, Eds. (National Institute of Water & Atmospheric Research Ltd., Wellington, New Zealand, 1996), pp. 213-226.
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    • All bryozoan fragments retained on 0.5-mm and larger screens were picked from 60 entire disaggregated 0.3-to 3.0-kg samples or, where bryozoans were extraordinarily abundant, from subsamples; fragments were sorted on the basis of clade, and total mass for each clade was determined directly or calculated on the basis of subsamples. Species that produce colony fragments typically smaller than 0.5 mm have not been included in most previous studies of bryozoan species diversity [summarized in (13)]. We have excluded such small size fragments from our calculations of relative skeletal mass as well; these fractions are subject to winnowing in many recent bryozoan habitats and are rarely derived from the ecologically dominant taxa. Nonetheless, small colonies of cyclostomes and cheilostomes may be numerous in some environments (E. Håkansson, personal communication). Our data were supplemented by data in O. Berthelsen, Danmarks Geol. Unders. 83, 1 (1962) and A. H. Cheetham, Smithsonian Contrib. Paleobiol. 6, 1 (1971). Some variation in the data inevitably results from variable amounts of cement or of matrix or shell fragments. Cyclostomes tend to have thinner walls than do cheilostomes, and raw cheilostome mass was weighted by 1.26 on the basis of a thin-section determination of the ratio of skeleton to cement plus adherent material in control samples [33 cheilostomes (X̄ = 0.62, SD = 0.147) and 35 cyclostomes (X̄ = 0.51, SD = 0.151) from four representative collections]. Additional "noise" in the data may be due to different taphonomic responses of cyclostome and cheilostome bryozoans in different environments. However, dissolution and abrasion rates of mineralized bryozoans are dependent upon diverse factors that cut across clade assignment [A. M. Smith, C. S. Nelson, P. J. Danaher, Palaeogeogr. Palaeoclimatol. Palaeoecol. 93, 213 (1992); A. M. Smith and C. S. Nelson, in Biology and Palaeobiology of Bryozoans, P. J. Hayward, J. S. Ryland, P. D. Taylor, Eds. (Olsen & Olsen, Fredensborg, Denmark, 1994), pp. 177-180; in Bryozoans in Space and Time, D. P. Gordon, A. M. Smith, J. A. Grant-Mackie, Eds. (National Institute of Water & Atmospheric Research Ltd., Wellington, New Zealand, 1996), pp. 213-226.
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    • All bryozoan fragments retained on 0.5-mm and larger screens were picked from 60 entire disaggregated 0.3-to 3.0-kg samples or, where bryozoans were extraordinarily abundant, from subsamples; fragments were sorted on the basis of clade, and total mass for each clade was determined directly or calculated on the basis of subsamples. Species that produce colony fragments typically smaller than 0.5 mm have not been included in most previous studies of bryozoan species diversity [summarized in (13)]. We have excluded such small size fragments from our calculations of relative skeletal mass as well; these fractions are subject to winnowing in many recent bryozoan habitats and are rarely derived from the ecologically dominant taxa. Nonetheless, small colonies of cyclostomes and cheilostomes may be numerous in some environments (E. Håkansson, personal communication). Our data were supplemented by data in O. Berthelsen, Danmarks Geol. Unders. 83, 1 (1962) and A. H. Cheetham, Smithsonian Contrib. Paleobiol. 6, 1 (1971). Some variation in the data inevitably results from variable amounts of cement or of matrix or shell fragments. Cyclostomes tend to have thinner walls than do cheilostomes, and raw cheilostome mass was weighted by 1.26 on the basis of a thin-section determination of the ratio of skeleton to cement plus adherent material in control samples [33 cheilostomes (X̄ = 0.62, SD = 0.147) and 35 cyclostomes (X̄ = 0.51, SD = 0.151) from four representative collections]. Additional "noise" in the data may be due to different taphonomic responses of cyclostome and cheilostome bryozoans in different environments. However, dissolution and abrasion rates of mineralized bryozoans are dependent upon diverse factors that cut across clade assignment [A. M. Smith, C. S. Nelson, P. J. Danaher, Palaeogeogr. Palaeoclimatol. Palaeoecol. 93, 213 (1992); A. M. Smith and C. S. Nelson, in Biology and Palaeobiology of Bryozoans, P. J. Hayward, J. S. Ryland, P. D. Taylor, Eds. (Olsen & Olsen, Fredensborg, Denmark, 1994), pp. 177-180; in Bryozoans in Space and Time, D. P. Gordon, A. M. Smith, J. A. Grant-Mackie, Eds. (National Institute of Water & Atmospheric Research Ltd., Wellington, New Zealand, 1996), pp. 213-226.
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    • note
    • Supported by the NSF (DEB 9306729 to S.L.; EAR 9117289 to F.K.M.), U.S.-U.K. Fulbright program (F.K.M.), National Geographic Society (F.K.M.), Petroleum Research Fund of American Chemical Society (F.K.M.), NASA (NAGW-1963 to J.J.S.J.), and Global Change and the Biosphere Programme of the National History Museum/University College London (P.D.T.). We thank S. Hageman, R. Lupia, and two anonymous reviewers for evaluating the manuscript and numerous colleagues who served as guides to field localities.


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