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New fossil discovery shows fish emerged on land with four limbs

The first known fossils of the rear-end of Tiktaalik roseae show that the first fish that crawled onto land to become land animals had a well-developed hind limb according to research published by Dr. Neil Shubin, Robert R. Bensley Distinguished Service Professor of Anatomy at the University of Chicago, and Dr. Edward Daeschler, Associate Curator of Vertebrate Zoology at the Academy of Natural Sciences of Drexel University, in the Jan. 13, 2014, issue of the journal Proceedings of the National Academy of Sciences.

This is a close up view of the hip bone of Tiktaalik roseae.
This is a close up view of the hip bone of Tiktaalik roseae.
University of Chicago, Kevin Jiang.
This is an updated illustration of Tiktaalik roseae in its natural environment.
University of Chicago, Neil Shubin.

Tiktaalik roseae is a transitional species between fish and the first legged animals that lived about 375 million years ago. The animal lived in freshwater and could reach lengths of nine feet. Tiktaalik roseae had gills, fins, and scales. The animal also had primitive lungs, a sturdy ribcage, and a movable neck.

Previously discovered specimens of Tiktaalik roseae have large front fins with well-developed shoulders and partial wrists. These features are thought to have allowed the animal to crawl.

The newly discovered rear halves of Tiktaalik roseae have a fully developed pelvic girdle with a hip socket that attached to long pelvic fins that were capable of supporting the fish on land.

The new discovery indicated that the first fish that crawled onto land most likely did so with four limbs. The previous theory that fish used only the front limbs to emerge onto land is not consistent with the new fossil evidence.