A robot inspired by mudskippers is helping researchers understand how vertebrates evolved to walk on land, offering valuable insights into the early stages of terrestrial life.

Watching a mudskipper awkwardly navigate its land-based activities might make you think it’s a newcomer to this world. These fish spend much of their time outside water, breathing through their skin and storing water in their mouths and gill chambers. Despite their seemingly clumsy movements, mudskippers are skilled enough to climb trees and effortlessly drag themselves across sand, mud, or slippery rocks using their pectoral fins. These traits make them excellent subjects for researchers aiming to understand how the first vertebrates made the leap from sea to land about 360 million years ago.

A recent study published in the journal Science delves into the fusion of biology, physics, and robotics, offering a theory on how ancient creatures accustomed to swimming in the warm Devonian oceans managed to adapt to the challenging task of moving across sand and mud as they began their journey onto land.

"A few years ago, we started exploring how newborn sea turtles manage to rapidly crawl down a beach at several body lengths per second," says Dan Goldman, an associate professor at the Georgia Tech School of Physics. "This led me to wonder about the complexity of the locomotor systems of the first vertebrates on land. What abilities did they possess as they made the shift to a fully terrestrial existence?"

In the past twenty years, robots have become more affordable and easier to construct, enabling scientists to create physical models of animals to study their movement. For this project, the team recognized that the mudskipper, which spends a significant amount of time on land but has relatively unsophisticated limbs for walking—putting it mildly—was likely the closest living animal to early vertebrates and our distant ancestors in terms of anatomy and behavior.

The research team observed live mudskippers and created mathematical and robotic models to explore how early land-dwelling creatures might have moved across various terrains, including gravel, sand, and mud—each presenting its own set of challenges. The findings suggest that early land vertebrates likely depended heavily on their tails for propulsion, compensating for any missteps made with their front fins or flippers. Check out the Georgia Tech video at the top of this article for an explanation of the entire process.

"Biomechanical models are typically done on solid ground," says Goldman. "We argue that the first substrates animals had to navigate were probably granular or flowable, making them more difficult to traverse, especially on inclined surfaces. What's fascinating is that both the robot and mathematical models revealed that while mudskippers use their tails to move across land, they do so with a remarkable level of control, which helps correct any errors made if their fins aren't properly positioned."

While this research takes us back in time to examine how the first land animals moved, it also holds the potential to shape our future by helping us create robots capable of navigating complex terrains, both here on Earth and on other planets.

"This fusion of biology, robophysics, and mathematics is a new and increasingly accessible field," says Goldman. "Although robots are still quite basic in their ability to traverse complex environments, we are now focusing on salamanders and investigating how extra limbs and the flexibility of their backs either enhance or limit their locomotion. This could pave the way for the development of more advanced robots capable of navigating real-world environments."