Sharks could walk before land animals

Sharks once walked underwater but fortunately for land-dwellers, this skill was not inherited by their toothy descendants.

Researchers from Curtin University have found evidence a common ancestor of sharks and mammals had the ability to walk on land 400 million years ago, millions of years before the first animals ever put four-feet on the ground.

In a paper published in Cell, the authors say they found the nerve networks required to walk on land when they examined the movement, gene expression and function of the little skate, a diamond-shaped member of the demersal fish family.

Study co-author Catherine Boisvert said the research pushed 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," she said.

The researchers observed footage which shows embryos of the little skate "walking" on the bottom of a tank. Their nerve impulses and gene expressions which control their fins were then recorded and compared to mammals and chickens.

The comparison, Dr Boisvert said, let researchers determine that the little skate had a similar nerve network to a four-footed animal.

The little skate could become a model for understanding the development of our limb nerve networks and their associated diseases.

The paper, The Ancient Origins of Neural Substrates for Land Walking, was co-authored by researchers from Monash University and New York University.

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