Here's some info. about the Devonian period...

During this period, which was approximately 408-360 million years ago during the Paleozoic Era, the Earth was undergoing an explosion of life. The oceans were dominated by brachiopods. These organisms looked like modern day clams or seashells and made their homes in cold water. Trilobites also roamed the oceans. Red algae built reefs all over the ocean. 4 diverse populations of fish rapidly evolved, ranging from large predators (like the first jawed fish), armored fish, and lobe finned fish. These produced the first tetrapods, or amphibians, that later led to four legged mammals.

On the land few plants had roots or leaves. There were mainly trimerophytes (leaves with a main stem and smaller branches). The late Devonian had ferns and moss that existed in the world's first forests. The few land animals were wingless insects and mites.

The mass extinction that took place primarily affected the marine community. All jawless fish, brachipods, and trilobites became extinct. The cause is under debate, but extinction occured either after a meteor impact or global cooling effects that deposited glacers in the water.