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‘Walking sharks’ strutted underwater first, new research finds

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Researchers have uncovered new information about the nerve networks required for walking on land, suggesting the last common ancestor of sharks and mammals walked underwater about 400 million years ago – 50 million years before land animals first walked the earth.

The paper in Cell published by Cell Press, found that the ability to walk on land was present for millions of years before the first four-footed animal set foot on land, after examining the movements, gene expression and function of the little skate, a dominant member of the demersal fish community.

Co-author Dr Catherine Boisvert from Curtin University’s School of Molecular and Life Sciences said the research challenged previous ideas, pushing the estimated time of land-walking back 50 million years.

“The nerve networks needed for walking were thought to be unique to land animals that transitioned from fishes around 380 million years ago, but our research has uncovered that the little skate and some basal sharks already had those neural networks in place,” Dr Boisvert said.

“We were able to determine these findings through footage that shows embryos of the little skate ’walking’ on the bottom of a tank. Their nerve impulses were then recorded and the gene expression in the nerves which control their fins were tested and compared to mammals and chickens.

“A list of genes activated in the nerves controlling the fins in the little skate was compiled and compared to the elephant shark and the catshark, showing they are conserved.”

By comparing the results, Dr Boisvert explained the researchers were able to determine that the little skate has a similar nerve network to a four-footed animal.

“This research is very significant as the little skate could become a very good model for understanding the development of nerve networks controlling our limbs and also reveal further information about the diseases associated with them,” Dr Boisvert said.

The research was also co-authored by researchers from New York University in the United States and Monash University.

The full research paper, The Ancient Origins of Neural Substrates for Land Walking, can be found online here.

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