Rhythms Of Life And Loss

365 MYA

The Devonian Period closes with another decline and mass extinction. Again, 50 percent of species vanish world-wide, the major losses taken this time by ocean life. Basic biota body blueprints remain conservative.

Note the "bottom-heavy" trend in evolution: new lineages generate remarkable diversity when they first appear, but settle to a limited number of body plans in what paleontologist Stephen Gould calls, "early experimentation and later standardization."

It takes 30 million years for biodiversity to recover fully from this mass extinction.

Exemplary of the way new life fills evolutionary niches, life grows in a tide pool. Climate and changes in the nature and distribution of habitats appear to drive most of the recent mass extinctions and extensive speciations which follow. Species capable of filling newly emptied niches do so rapidly. (Photography by Lois Brynes)

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