Ichthyostega stensioei

This sea creature was one of the first vertebrates (animals with backbones) to develop a set of legs and lungs and take a step on dry land. About 365 million years ago, Ichthyostega developed the ability to breathe air and ventured out of the sea. One of the earliest known amphbians, Ichthyostega still did its share of swimming, but it had four legs and could move around on land. It led the march that resulted in dozens, and then ultimately millions, of animal species living on land."Let There Be Legs! Ichthyostega was one of the first known tetrapods (creatures with four legs), Its legs, complete with toes, were the result of evolutionary transformation from fins over many thousands of years.""Munchies: Though it could walk, Ichthyostega spent most of its time in the water, powered by its wide tail. Its upper teeth, which were more than one-half inch long, stabbed into prey, while its smaller, lower teeth ground victims into tiny pieces."

Land Lubber
Before the Devonian period (408-360 million years ago), only plants, bacteria and a few arthropods (ancient crab-like creatures) lived on land. But all of that changed when Ichthyostega stepped out. This creature started its life with gills, yet over time developed lungs and the ability to breathe air, becoming one of the world's first amphibians. It paved the way for all land-living vertebrates, from frogs to bears and even to humans. This creature's direct descendants had all died out by about 360 million years ago. "Swamp Thing: Some think that Ichthyotega was too heavy, and its legs too weak, for it to walk well on high and dry land. These experts say that the amphibian used its legs to wade through shallow swamps that covered Greenland 365 million years ago.""Smooth Skin: This ancient amphibian had skin typical of its modern relatives-slimy to help keep in moisture when exposed to the sun. Some say it had small scales in places, leftovers from its ancestors, which were fish."