For the past 375 million years, the Canadian Arctic has been hiding long sought-after clues that hold prized information about how the ability to walk on land evolved. A study headed by University of Chicago biologist Neil Shubin and published January 13th in Proceedings of the National Academy of Sciences describes these ancient relics – fossils belonging to the “fishapod” Tiktaalik roseae.
100 million years before the first dinosaurs, Tiktaalik roseae was living in shallow water habitats – and most paleontologists would characterize this creature as a fish – but it had a number of transitional features that puts it somewhere along the evolutionary line between fish and tetrapod – thus the name “fishapod.”
Tiktaalik looked like a crocodile with fins and a more streamlined body. According to the 10 currently uncovered Tiktaalik fossils, it grew anywhere from 3 feet long up to 9 feet long. In its heyday 12 million years before the first 4-legged land-walkers, Tiktaalik sported the beginnings of the four limbs common to tetrapods today.
According to research from 2004, in which the first Tiktaalik fossils were described, this creature used its front limbs to crawl out of water, and only adapted to have rear walking legs when fully on land. But Shubin’s new study uses new fossils to show that Tiktaalik actually evolved all four limbs while still living in shallow waters – meaning that rear-limb locomotion actually originated in fish.
The research team compared front and rear appendages of Tiktaalik and found that they were about equal in relative strength and complexity. Tiktaalik had a pelvic bone that appeared to be an intermediate between what is typically seen in fish and the jointed pelvis characteristic of tetrapods.
Not only that, but Shubin and colleagues found Tiktaalik had a number of other transitional features. The fishapod breathed with early lungs – not quite the lungs of tetrapods but more advanced than gills. It also had a mobile neck, shoulders, elbows, and wrists.
Tiktaalik roseae has struck again, and paleontologists hope this mysterious creature will continue to make us rethink and challenge persisting views about the evolution of terrestrial life.
Shubin, N. H., Daeschler, E. B., & Jenkins, F. A. (2014). Pelvic girdle and fin of Tiktaalik roseae. Proceedings of the National Academy of Sciences, 111(3), 893-899.
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