Unusual Walking Fish Could Help Explain How Ancient Animals Switched From Water To Land

A living fish with the ability to walk could help scientists better understand how a group of ancient fish began exploring land and eventually evolved into tetrapods, which comprised the first four-limbed vertebrates and their descendants, according to a new study.

Scientists know that ancient fish began exploring living conditions on land nearly 400 million years ago, a move that ultimately led to the evolution of amphibians, reptiles, birds and mammals. However, exactly how the prehistoric fish used their bodies and fins in a terrestrial environment has so far remained a mystery.

“Stressful environmental conditions can often reveal otherwise cryptic anatomical and behavioral variation, a form of developmental plasticity,” Emily Standen of the University of Ottawa and the study’s lead author said, in a statement. “We wanted to use this mechanism to see what new anatomies and behaviors we could trigger in these fish and see if they match what we know of the fossil record.”

In order to study how this unique transition took place, the researchers turned to a living African fish, called Polypterus, which can breathe air, walk on land and looks much like the ancient fish that evolved into tetrapods. As part of the study, published in the journal Nature, the researchers raised juvenile Polypterus on land for nearly a year to see how these “terrestrialized” fish moved differently.

According to researchers, the results showed significant anatomical and behavioral changes in the fish as they walked more effectively by placing their fins closer to their bodies. They lifted their heads higher, and had fins that slipped less often than that of waterborne fish.

The fish also underwent changes in their skeletons and musculature, which helped them become more elongate with stronger attachments across their chest, possibly for better support during walking.

“Because many of the anatomical changes mirror the fossil record, we can hypothesize that the behavioral changes we see also reflect what may have occurred when fossil fish first walked with their fins on land,” Hans Larsson, a vertebrate paleontologist at McGill University, said in the statement.

Video source: McGill University