Fossil Evidence

  • By Rima Chaddha
  • Posted 11.01.07
  • NOVA

In 2004, scientists digging in the Canadian Arctic unearthed fossils of a half-fish, half-amphibian that all but confirmed paleontologists' theories about how land-dwelling tetrapods–four-limbed animals, including us–evolved from fish. It is a classic example of a transitional form, one that bridges a so-called evolutionary gap between different types of animal. In this slide show, examine five important cases.

Launch Interactive Printable Version

Examine five transitional species that fill so-called gaps in the fossil record.


Anya Vinokour
Amanda Clarke
Brenden Kootsey


(all illustrations)
© NOVA/WGBH Educational Foundation
(nerve cells)
© Image Source/Corbis
(red blood cells)
© Micro Discovery/Corbis
(Hox genes of fly, Hox genes of mouse)
adapted by Cold Spring Harbor Laboratory Press/original image © Sinauer Associates, Inc.
(stained fly embryo, fly images, imaginal disk images)
Courtesy Nipam Patel
© Julie Merchant/

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