Early Land Dwellers Had Trouble Walking

Early land animals may have had a tough time learning how to walk after living in the sea. According to a 3-D model of the dog-sized Ichthyostega, it most likely used only two of its legs for locomotion and instead "flopped" around on land.

Researchers previously thought the animal, one of the earliest tetrapods known to have crept onto land, moved around much like a salamander. The model suggests, however, that Ichthyostega did not have the range of motion necessary for a four-legged gait. In fact, its hind legs probably barely touched the ground, and its movement was more akin to the modern-day mudskipper fish.

"When Ichthyostega fossils were first being found in Greenland in the 1920s, the natural assumption was that something with four limbs with digits could walk," said paleontologist Stephanie Pierce, of the Royal Veterinary College in London. "We definitely know that they were moving more like a mudskipper than [like] modern tetrapods."

In order to create the model, Dr. Pierce and her colleagues scanned an almost complete fossil of  Ichthyostega named "Mr. Magic." They used bones from 12 other Ichthyostega specimens to fill in any bones that were missing.

Land animals with four limbs and skeletons first came about in the water. It wasn't until millions of years later, during the Devonian period, that they ventured out of the water and onto land. The earliest record we have of this phenomena dates back to around 390 million years ago. The first record of Ichthyostega that we have goes to around 360 million years ago.

The 3-D model is a valuable tool for scientists to further study the transition that took animals out of the water and onto land.

"The land was an open ecological niche, free to be exploited, and these early tetrapods knew what to do. It was theirs for the taking," Pierce said. "We want to see how they navigated this new environment."