Great Transitions Interactive

Darwin predicted that there would be fossils of creatures with features that are intermediate between those of ancestral and modern groups. Yet, when he published On the Origin of Species, no such fossils were known. Since that time, many transitional fossils have been found, providing evidence for the evolutionary origin of key anatomical structures.

The Origin of Tetrapods
The evolution of four-limbed animals, or tetrapods, from fish is a dramatic example of one of the great evolutionary transitions in the history of life. Explore transitional forms with features of both fish and tetrapods, and see the progression of anatomical changes from reconstructed fossil skeletons.

11/18/2015: Version 2.0 now includes Coelacanth.