Salamander May Reveal How Animals First Evolved to Walk on Land

About 390 million years ago, the first vertebrate animals moved from water to land. Now, scientists are learning a bit more about how this evolution occurred.

In this latest study, the researchers looked at the tiger salamander to find evolutionary clues as to how animals moved from sea to land. Salamanders are particularly good animals to study since they show how locomotion onto land evolved, since their anatomy and ecology is similar to the earliest tetrapods found in the fossil record.

Bones must regularly withstand a variety of forces, or "loads," from both the contraction of muscles and interaction with the environment. Limb bones, in particular, must accommodate some of the highest forces. This is particularly true when animals evolved from sea to land.

The researchers actually tested the mechanics of bone loading in salamanders in a variety of ways, including filming salamanders as they walked across a custom-built platform that measured forces on the limb bones. The scientists then compared the forelimbs and hind limbs and the limb joints. They also constructed mathematical models to evaluate how the limb bones were able to withstand the physical demands of walking on land.

So what did they find? It turns out that the forelimbs, compared to the hind limbs, had lower yield stresses, higher mechanical hardness, and a greater ability to withstand loads higher than normal. This may reveal how tetrapods took their first steps on land. By comparing unique contributions of forelimbs and hind limbs, scientists may be able to piece together exactly how these animals physically moved on land.

The findings are published in the Journal of Experimental Biology.

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