Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 242, Issue 3-4, Pages 240-253Publisher
ELSEVIER
DOI: 10.1016/j.epsl.2005.12.007
Keywords
evolution; proteromorphosis; atavisms; environmental stress; ammonoids; silicoflagellates; planktonic organisms
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This paper describes the influence of high environmental stress on evolutionary trends in some selected Mesozoic ammonite lineages and some protists. During extinction periods, many ammonoids are affected by drastic simplifications of their shell geometry, ornamentation and suture line. We observe that relatively tightly coiled ammonites can give rise to highly evolute forms or uncoiled heteromorphs with simple ornamentation and almost ceratitic suture line-a phenomenon called proteromorphosis. Such simplifications often correspond to a reappearance of ancestral geometries (primitive ornamentation, evolute coiling or uncoiling) which suggest that the evolutionary clock of these organisms can be reinitialized by extreme, sublethal, environmental stress such as giant volcanism (including its consequences on diverse pollutions and on climatic changes) and major regressive events. (c) 2006 Elsevier B.V. All rights reserved.
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