Tiktaalik Fossils Reveal Key Link in Evolution of Hind Limbs

Posted on January 14, 2014

Fossils of Tiktaalik, an ancient fish and crocodile-like creature, reveal a key link in the evolution of hind limbs. Tiktaalik roseae lived 375 million years ago. The creatures had large forefins with shoulders, elbows and partial wrists. Scientists believe Tiktaalik was able to support itself on ground using its forefins. The scientists say the creature represents the best-known transitional species between fish and land-dwelling tetrapods.

Tiktaalik was about 9 feet long. It had gills, scales, fins, primitive lungs, robust ribcage and a mobile neck. It had a flat head and sharp teeth. The scientists say the creature had a pelvis that is comparable to some early tetrapods.

The fossils are described in an article published in the Proceedings of the National Academy of Sciences. It is the inaugural article for Prof. Neil Shubin, Robert R. Bensley Distinguished Service Professor of Anatomy at the University of Chicago, as a member of the National Academy of Sciences.

Prof. Shubin says in a statement, "Previous theories, based on the best available data, propose that a shift occurred from 'front-wheel drive' locomotion in fish to more of a 'four-wheel drive' in tetrapods. But it looks like this shift actually began to happen in fish, not in limbed animals."

Study co-author Edward Daeschler, associate curator of Vertebrate Zoology at the Academy of Natural Sciences of Drexel University, says of the Tiktaalik pelvis, "This is an amazing pelvis, particularly the hip socket, which is very different from anything that we knew of in the lineage leading up to limbed vertebrates. Tiktaalik was a combination of primitive and advanced features. Here, not only were the features distinct, but they suggest an advanced function. They appear to have used the fin in a way that's more suggestive of the way a limb gets used."

The scientists say its possible Tiktaalik may have used its hind fins to walk underwater like the lungfish. You can view a video of a lungfish walking here.

The first Tiktaalik roseae was fossil was discovered in 2004. It was nicknamed a "fishapod" at the time. You can read more about it here.

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