Morphometrics of the Paleocene coccolith genera Cruciplacolithus, Chiasmolithus , and Sullivania : a complex evolutionary history

Investigation of the evolution of calcareous nannoplankton is hindered by the extremely small size (5-10 μm) of their fossils. We introduce new technology, a scanning electron microscope connected to an image analysis system (SEM-IAS), which allows this field to be explored as never before. This sys...

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Bibliographic Details
Published in:Paleobiology
Main Authors: Bralower, Timothy J., Parrow, Matthew
Format: Article in Journal/Newspaper
Language:English
Published: Cambridge University Press (CUP) 1996
Subjects:
Paleontology
General Agricultural and Biological Sciences
Ecology
Ecology, Evolution, Behavior and Systematics
Weddell Sea
Weddell
Antarc*
Antarctica
North Atlantic
Online Access:http://dx.doi.org/10.1017/s009483730001633x
https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S009483730001633X
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Summary:Investigation of the evolution of calcareous nannoplankton is hindered by the extremely small size (5-10 μm) of their fossils. We introduce new technology, a scanning electron microscope connected to an image analysis system (SEM-IAS), which allows this field to be explored as never before. This system enables a host of morphocharacters to be measured and included in studies of phylogeny and evolutionary dynamics. We have applied the SEM-IAS to study the evolution of Paleocene coccolith genera Cruciplacolithus, Chiasmolithus , and Sullivania. A variety of detailed measurements have been made on over 4000 coccoliths from Deep Sea Drilling Project Site 384 in the temperate North Atlantic and Ocean Drilling Program Site 690 in the Weddell Sea off Antarctica. Our results indicate no simple relationships between morphocharacters, the shapes of all three genera are both complex and highly variable. Although most morphocharacters possess little phylogenetic significance, the areas of different shield cycles show gradual divergence between Chiasmolithus and Sullivania through the Paleocene. Change of most other morphocharacters occurs at variable rates and reversals in trends are common. Minimal correlation exists between the trends and oscillatory shape changes observed at the two sites. We conclude that these trends and oscillations represent local, transitory ecophenotypic variation of the complex form. There is little stasis in the ten-million-year record studied.

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