African Lungfish Walk in Water: Study Suggests Four-Legged Locomotion Began at Sea
Bascom, Nick, Science News
African lungfish walk and bound along the bottoms of water tanks on their slender, whiplike pelvic fins, a new study finds.
Lungfish are closely related to some of the earliest four-legged terrestrial vertebrates, or tetrapods. The findings suggest that these transitional creatures learned to scuttle across the floors of ancient seas before they took to land and developed more complex limbs with digits, biologist Heather King and colleagues at the University of Chicago suggest online December 12 in the Proceedings of the National Academy of Sciences.
"The cool thing about the lungfish is that it's walking underwater," says King. "And if lots of tetrapods were also doing this, it could mean that the first step in the evolution of vertebrate walking took place underwater."
Around 400 million years ago, certain species of bony fish--called the lobe-finned fishes for their muscular, fleshy fins--began to evolve features such as larger limbs with digits, which allowed them to move onto land. "We have a whole series of fossils that show this transition from lobe-finned fishes to tetrapods," says King. Until now, however, scientists didn't have a clear idea of the order in which these features emerged.
"The fossil record has limitations," says study coauthor Neil Shubin. "Living organisms are far weirder than you can imagine, and the more you look the more you find."
To get a closer look at one of the last living species of lobe-finned fish, the research team plopped African lungfish of the species Protopterus annectans one at a time into a tank with a plastic mesh bottom and trained several cameras on them. …