CLAUS LUNAU / SCIENCE PHOTO LIBRARY CLAUS LUNAU / SCIENCE PHOTO LIBRARY
Tiktaalik prehistoric fish, illustration. This extinct lobe-finned fish lived during the Late Devonian period (375 million years ago). A Tiktaalik roseae fossil was found in the Canadian Arctic in 2004. When scientists later analysed its skull, it was found to demonstrate a key transitional stage between fish and tetrapods (four-limbed vertebrates). It had fish-like fins with thin ray bones and scales, but also a flattened skull (similar to a crocodile), a mobile neck, sturdy shoulders, lungs, and ribs, features characteristic of tetrapods. Tiktaalik roseae is thought to have lived in shallow water, using its fins to prop itself up.
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