It is a common belief that life on Earth began in the ocean with floating cells and evolved into swimming fishes and other animals. Then, these animals evolved into vertebrates that could breathe outside the water. And finally, these animals moved to land, after which they developed the skill of walking. However, new research suggests this chronology might be a misunderstanding. It is possible that our very ancient ancestors started walking in the ocean itself, millions of years before their successors moved on to land.
The first clue of such animals was discovered in 2018 when scientists discovered little skate fish (Leucoraja erinacea) were capable of footing on the ocean floor and they used neural circuits like we use to walk today.The skate fish is one of the most primitive animals with a backbone. It originated more than 400 million years ago whereas our estimated move from ocean to land is roughly 380 million years ago. This would suggest the act of walking precedes the existence of land-based vertebrates.
Mathematicians used video data on the scuttling dynamics of these creatures to simulate a model to analyse and investigate how early leg-like motions could have evolved in the deep sea. The result in a neutrally buoyant environment suggests an efficient, controlled, and balanced type of walking. There is even some left-foot right-foot waddle similar to today’s skate. The paper described the movement as “energy-efficient locomotion.”
In the model, 4 episodes/repetitions led to a one-legged locomotion strategy. After 200 episodes, a two-legged pattern emerged. After 600 episodes, left-right alternate steps could be observed. A total of 5,000 episodes were created.While it’s not exactly clear why the skates started walking, some believe it could be more energy efficient than swimming at the same pace.
“As our ancient ancestors transitioned to land, the control strategy likely became more complex. But in reliably homogeneous environments, like the seafloor, perhaps a simple strategy was all that was needed,” said Lakshminarayanan Mahadevan, an applied mathematician from Harvard University.
Their study named Models of benthic bipedalism has been published in Royal Society Publishing.