One of the greatest fulfilled predictions of evolutionary biology is the discovery, in 2004, of a transitional form between fish and amphibians. This is the fossil species ‘Tiktallik rosae,’ which tells us a lot about how vertebrates came to live on the land. Its discovery is a stunning vindication of the theory of evolution.

Until about 390 million years ago, the only vertebrates were fish. But, 30 million years later, we find creatures that are clearly ‘tetrapods: four-footed vertebrates that walked on land. Those early tetrapods were like modern amphibians in several ways: they had flat heads and bodies, a distinct neck, and well-developed legs and limb girdles. Yet they also show strong links with earlier fishes, particularly the group known as “lobe-finned fishes,” so called because of their large bony fins that enables them to prop themselves up on the bottom of shallow lakes or streams. The fishlike structures of early tettrapods include scales, limb bones, and head bones. - page 36