What Were the Dominant Organisms Living During the Tertiary Time Period?


The Tertiary Period marked the dawn of the Age of Mammals, beginning 65 million years ago and lasting 63 million years. The mass extinctions that saw the rapid disappearance of the dinosaurs and other large species were complete when the Tertiary began. With the disappearance of the large reptiles, new opportunities for other species arose.

The Facts

  • In the 1800s, scientists divided geological time into four periods using Latin terminology for numbering. Today, geologists commonly use a different naming system, under which the Tertiary Period corresponds with the Paleogene and first half of the Neogene periods.

Age of Mammals

  • Mammals were the dominant organisms during the Tertiary Period. With the dinosaurs and other large species gone, mammals were able to thrive and diversify.


  • During the Tertiary Period, the climate was cooling from tropical temperatures and slid into a full-fledged Ice Age by the end.


  • As the climate cooled, many landscapes changed from forest to large grasslands. These grasslands supported large herds of grazing mammals.

Other Organisms

  • Birds also flourished during the Tertiary Period. Bony fish like trout and bass evolved and sharks became plentiful. An abundance of flowering plants meant that insect species also multiplied.

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  • "Biology: Concepts and Connections;" Neil A. Campbell; 2009
  • Tertiary Period
  • Photo Credit "Mother and baby gorilla" is Copyrighted by Flickr user: mape_s (Marieke IJsendoorn-Kuijpers) under the Creative Commons Attribution license.
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