Evolution of Complexity in Paleozoic Ammonoid Sutures

+ See all authors and affiliations

Science  22 Oct 1999:
Vol. 286, Issue 5440, pp. 760-763
DOI: 10.1126/science.286.5440.760

You are currently viewing the abstract.

View Full Text


The septal sutures of 588 genera of Paleozoic ammonoids showed a 1600 percent increase in mean complexity over 140 million years. Within 475 ancestor/descendant pairs, descendants were more than twice as likely to be more complex than their ancestors. Twelve subclades (373 genera) averaged 34 percent increased complexity. These patterns are compatible with an active or driven system of long-term bias for increased complexity. Mass extinctions acted in opposition to this long-term trend, tending to eliminate more-complex forms and resetting the trend with each extinction event.

  • * To whom correspondence should be addressed. E-mail: wsaunder{at}

View Full Text