Phyletic gradualism in a Late Cenozoic planktonic foraminiferal lineage; DSDP Site 284, southwest Pacific
Shape measurements have been made on planktonic foraminifera from a South Pacific Late Miocene to Recent temperate evolutionary lineage ( Globorotalia conoidea through intermediate forms to G. inflata in DSDP Site 284). The sampling interval is about 0.1 Myr over nearly 8 Myr. Gradual evolution (phy...
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Language: | English |
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Cambridge University Press (CUP)
1981
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Online Access: | http://dx.doi.org/10.1017/s0094837300004000 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0094837300004000 |
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crcambridgeupr:10.1017/s0094837300004000 2024-06-23T07:56:17+00:00 Phyletic gradualism in a Late Cenozoic planktonic foraminiferal lineage; DSDP Site 284, southwest Pacific Malmgren, Björn A. Kennett, James P. 1981 http://dx.doi.org/10.1017/s0094837300004000 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0094837300004000 en eng Cambridge University Press (CUP) https://www.cambridge.org/core/terms Paleobiology volume 7, issue 2, page 230-240 ISSN 0094-8373 1938-5331 journal-article 1981 crcambridgeupr https://doi.org/10.1017/s0094837300004000 2024-06-05T04:04:15Z Shape measurements have been made on planktonic foraminifera from a South Pacific Late Miocene to Recent temperate evolutionary lineage ( Globorotalia conoidea through intermediate forms to G. inflata in DSDP Site 284). The sampling interval is about 0.1 Myr over nearly 8 Myr. Gradual evolution (phyletic gradualism) clearly occurs in all but one measured parameter. No clear evidence exists for abrupt evolutionary steps (punctuated equilibria) within the bioseries. If they occur, they are the exception rather than the rule. The number of chambers in the final whorl decreases almost linearly, despite known paleoceanographic oscillations within the temperate water mass. Mean size and apertural shape variations seem to correlate with paleoceanographic change. It is speculated that certain major morphological changes that took place within this evolutionary bioseries (i.e. loss of keel, rounding of periphery) developed in response to a major latest Miocene cooling, associated with instability in the water column and resulting adjustments of the test structure to water density changes. Changes exhibited in shape measurements may offer a precise method of stratigraphic correlation between temperate South Pacific Late Cenozoic sequences. Four species and two subspecies, long recognized to form the basis of this lineage, are redefined biometrically. Article in Journal/Newspaper Planktonic foraminifera Cambridge University Press Pacific Paleobiology 7 2 230 240 |
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Open Polar |
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Cambridge University Press |
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crcambridgeupr |
language |
English |
description |
Shape measurements have been made on planktonic foraminifera from a South Pacific Late Miocene to Recent temperate evolutionary lineage ( Globorotalia conoidea through intermediate forms to G. inflata in DSDP Site 284). The sampling interval is about 0.1 Myr over nearly 8 Myr. Gradual evolution (phyletic gradualism) clearly occurs in all but one measured parameter. No clear evidence exists for abrupt evolutionary steps (punctuated equilibria) within the bioseries. If they occur, they are the exception rather than the rule. The number of chambers in the final whorl decreases almost linearly, despite known paleoceanographic oscillations within the temperate water mass. Mean size and apertural shape variations seem to correlate with paleoceanographic change. It is speculated that certain major morphological changes that took place within this evolutionary bioseries (i.e. loss of keel, rounding of periphery) developed in response to a major latest Miocene cooling, associated with instability in the water column and resulting adjustments of the test structure to water density changes. Changes exhibited in shape measurements may offer a precise method of stratigraphic correlation between temperate South Pacific Late Cenozoic sequences. Four species and two subspecies, long recognized to form the basis of this lineage, are redefined biometrically. |
format |
Article in Journal/Newspaper |
author |
Malmgren, Björn A. Kennett, James P. |
spellingShingle |
Malmgren, Björn A. Kennett, James P. Phyletic gradualism in a Late Cenozoic planktonic foraminiferal lineage; DSDP Site 284, southwest Pacific |
author_facet |
Malmgren, Björn A. Kennett, James P. |
author_sort |
Malmgren, Björn A. |
title |
Phyletic gradualism in a Late Cenozoic planktonic foraminiferal lineage; DSDP Site 284, southwest Pacific |
title_short |
Phyletic gradualism in a Late Cenozoic planktonic foraminiferal lineage; DSDP Site 284, southwest Pacific |
title_full |
Phyletic gradualism in a Late Cenozoic planktonic foraminiferal lineage; DSDP Site 284, southwest Pacific |
title_fullStr |
Phyletic gradualism in a Late Cenozoic planktonic foraminiferal lineage; DSDP Site 284, southwest Pacific |
title_full_unstemmed |
Phyletic gradualism in a Late Cenozoic planktonic foraminiferal lineage; DSDP Site 284, southwest Pacific |
title_sort |
phyletic gradualism in a late cenozoic planktonic foraminiferal lineage; dsdp site 284, southwest pacific |
publisher |
Cambridge University Press (CUP) |
publishDate |
1981 |
url |
http://dx.doi.org/10.1017/s0094837300004000 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0094837300004000 |
geographic |
Pacific |
geographic_facet |
Pacific |
genre |
Planktonic foraminifera |
genre_facet |
Planktonic foraminifera |
op_source |
Paleobiology volume 7, issue 2, page 230-240 ISSN 0094-8373 1938-5331 |
op_rights |
https://www.cambridge.org/core/terms |
op_doi |
https://doi.org/10.1017/s0094837300004000 |
container_title |
Paleobiology |
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7 |
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2 |
container_start_page |
230 |
op_container_end_page |
240 |
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1802649269133377536 |