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amphibians land-dwelling

Some early land-dwelling amphibians evolved back to aquatic species

By Riley Black Illustration of the temnospondyl species Prionosuchus plimmeriJAMES KUETHER/SCIENCE PHOTO LIBRARY One of the greatest transitions in evolutionary history was the emergence of tetrapods, or four-legged vertebrates, onto land. By about 340 million years ago, fins had become fingers and limbs, shoulder and hip joints had changed to bear weight, and an array…

By Riley Black

ancient amphibian

Illustration of the temnospondyl species Prionosuchus plimmeri

JAMES KUETHER/SCIENCE PHOTO LIBRARY

One of the best transitions in history has been the emergence of tetrapods, or four-legged vertebrates, onto territory. By about 340 million years back, fins had turned into palms and limbs, hip and shoulder joints had changed to bear weight, and an array of amphibious animals had begun to live along the water’s edge. However, an investigation of some early tetrapods now indicates that long after they left a home on property, some species became adapted to life in all over again.

Aja Mia Carter at the University of Pennsylvania and her colleagues focused on a group of early amphibians known as temnospondyls, roughly salamander-like tetrapods that spun off a great diversity of species between 295 and 330 million decades ago.

Rather than looking in the limbs of these animals, though, Carter and her team analysed the backbone anatomy of more than a dozen temnospondyl species. They also used a previously published evolutionary tree to comprehend how these species were interrelated, and searched the scientific literature for information about the likely lifestyles of each — specifically whether it was either more aquatic or terrestrial.

Temnospondyls, the researchers found, most likely evolved by a land-dwelling ancestor. Surprisingly, from there, a few species shifted course and became adapted to life in water all over again within an evolutionary reversal.

The study also revealed that relatively stiff backbones were not an adaptation to life on land. Researchers have generally assumed that ancient land animals evolved a stiffer spine to help support their own bodies, but it was actually the water-dwelling temnospondyls that had a more rigid spine.

“I was stunned to see that between individual vertebrae, aquatic species were stiffer than terrestrial species,” says Carter. To put it differently, a stiffened spine wasn’t essential for these ancient amphibians to walk on land.

“This study is resetting how we think about locomotion

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