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An unusual species of fish that can walk and breathe air shows that these animals may be more capable of adapting to life on land than previously thought, researchers say.
The new findings may help explain how the ancient fish ancestors of humans colonized the land.
The evolution of the ancient fish that switched from living in water to living on land about 400 million years ago is one of the most pivotal moments in the history of the animal kingdom. These first four-limbed animals, known as stem tetrapods, ultimately gave rise to amphibians, reptiles, birds and mammals.
Just how ancient fish made the shift to terrestrial life still remains largely a mystery. To learn more about what happened, scientists investigated the bichir (Polypterus senegalus), a modern African fish that has lungs for breathing air, and stubby fins it can use to pull itself along on land. The bichir possesses many traits similar to ones seen in fossils of stem tetrapods, the researchers said.
The scientists raised groups of bichir on land for eight months to find out how they would differ from bichir raised in the water. They found that the land-raised fish lifted their heads higher, held their fins closer to their bodies, took faster steps, undulated their tails less frequently and had fins that slipped less often than bichir raised in water. The land-raised fish also underwent changes in their skeletons and musculature that probably paved the way for their changes in behavior. All in all, these alterations helped bichir move more effectively on land.
The results suggest that the bichir is more malleable during its development than previously thought. This plasticity is what made this fish capable of growing up very differently depending on its environment, and the researchers suggest that stem tetrapods were similarly adaptable.
University of Ottawa biologist Emily Standen and her colleagues Hans Larsson and Trina Du of McGill University's Redpath Museum detailed their findings in Thursday's issue of the journal Nature.