Is the direction of coiling in the early stages of an evolution of planktonic foraminifera at random? (50% right and 50% left)
Bolli assumed. that at the beginning of an evolutionary trend of planktonic Foraminifera the coiling direction should be at random. Two sequences of such trends were studied, the one of the Globigerina-cretacea-gens (Praeglobotruncana infracretacea- P. gautierensis) in the Albian of Holland, the oth...
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| Format: | Article in Journal/Newspaper |
| Language: | English |
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ITGE
1972
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| Online Access: | https://oceanrep.geomar.de/id/eprint/36430/ https://oceanrep.geomar.de/id/eprint/36430/1/Hofker.pdf |
| Summary: | Bolli assumed. that at the beginning of an evolutionary trend of planktonic Foraminifera the coiling direction should be at random. Two sequences of such trends were studied, the one of the Globigerina-cretacea-gens (Praeglobotruncana infracretacea- P. gautierensis) in the Albian of Holland, the other of the Globigerina (Globoconusa)- daubjergensis-gens in the Danian of Denmark, to verify this assumption. Both sequences show that in the beginning of an evolutionary trend the percentages of right coiling are distinctly less than 50 % and that later in the evolution the random coiling direction is transgressed towards dominant right coiling. The eventual causes of sudden regressions towards left coiling are discussed. |
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