The transition from animals living in water to living on land is one of the most pivotal moments in evolution. This evolution is believed to have occurred about 400 million years ago as ancient fish made their way on land. The first four-limbed animals are known as stem tetrapods, and would eventually become the amphibians, birds, reptiles and mammals we see today.

How the ancient fish used their bodies designed more for the water on land is what scientists aimed to find out in a new study.

Researchers at McGill University turned their eyes to a living fish to show how ancient fish may have looked when they first exited the water. The fish, called Polypterus senegalus, is native to Africa and can breathe air and ‘walk’ on land.

The researchers raised juvenile Polypterus for almost a year to see what changes would happen to “terrestrialized” fish.

“Stressful environmental conditions can often reveal otherwise cryptic anatomical and behavioural variation, a form of developmental plasticity”, says Emily Standen, a former McGill post-doctoral student who led the project, now at the University of Ottawa. “We wanted to use this mechanism to see what new anatomies and behaviours we could trigger in these fish and see if they match what we know of the fossil record.”

Here’s what they found. The fish showed incredible changes. A terrestrial sized fish was able to walk more effectively by lifting their heads higher and keeping their fins closer to their bodies. Skeletal changes also occurred.

“Anatomically, their pectoral skeleton changed to become more elongate with stronger attachments across their chest, possibly to increase support during walking, and a reduced contact with the skull to potentially allow greater head/neck motion,” says Trina Du, a McGill Ph.D. student.

The fish quickly adapted to their new environment with changes to its muscles and bones. It’s an incredible look at how ancient species may have transitioned from water to land. Check out the video below for more.

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