Walking Fish Reveal How Our Ancestors Evolved Onto Land (Watch Video)

The evolution of the fish has been a huge mystery until now. Around 400 million years ago, the fish began exploring land and evolved into tetrapods that are today's amphibians, reptiles, birds and mammals. Scientists are still intrigued by the way in which these aquatic creatures were able to use their bodies and fins to move on land and conform to the environment. The manner by which they could do this is still unknown.

To understand how these fishes left their environment and began walking on land, a study was conducted by the McGill University researchers. They conducted this research on a fish called the Polypterus. Found in Africa, the Polypterus can breathe air and move on land, and it closely resembles the ancient fishes that evolved into tetrapods. The researchers not only sought to understand the fish's evolutionary process but also wanted to know these "terrestrialized" fish were different in their movement and appearance. For this purpose, they raised these juvenile fishes for almost a year.

Emily Standen, a former McGill post-doctoral student who led the project and now at the University of Ottawa, said that usually in a stressful environment otherwise cryptic anatomical and behavioural variation can be seen "a form of developmental plasticity." She went on to add that they wanted to use this mechanism to trigger changes in these fish that would lead to physical as well as behavioural changes. They then wanted to compare them with the fossil records of the ancient fish.

The unique experiment called The Terrestrialized Polypterus Experiment aimed at giving some insight into how these fossil fishes could have used their fins to move in a terrestrial environment and the way they could have evolved.

What they then noticed was astonished them, there were significant changes in these fishes' anatomy and behaviour. They adapted to the environment and began walking with their fins close to the body. The movement of their heads also changed - they lifted their head higher and kept their fins from slipping.

Trina Du, a McGill PhD student and study collaborator, explained that anatomically, their pectoral skeleton elongated more and more with stronger attachments across their chest. This they did to increase support during walking, "and a reduced contact with the skull to potentially allow greater head/neck motion," she said

Hans Larsson, Canada Research Chair in Macroevolution at McGill University and an associate professor at the Redpath Museum, explained that many of the changes that were observed in these fish matched the fossil records. They realised that the behavioural changes seen also matched the fossil fish. He was of the opinion that the same changes could have happened when the fossil fish had walked using their fins on land.

"This is the first example we know of that demonstrates developmental plasticity may have facilitated a large-scale evolutionary transition, by first accessing new anatomies and behaviours that could later be genetically fixed by natural selection", said Larsson

The study is published in the journal Nature.

Source: YouTube/ McGill University