"Before the Ice Age, before the first human...before even the dinosaurs. The Ordovician is a mindbogglingly 450 million years ago, so far back that planets had yet to evolve."
The Ordovician was an early period in Earth's history. Although nearly all of life in Ordovician was underwater, some arthropods like the eurypterids, ventured onto land, mainly to mate.
During this Ordovician, plants had not evolved yet, as the atmosphere of the Ordovician was dreadful. There was much less oxygen but even far more carbon dioxide. Much like the previous Cambrian period, during the Ordovician, there wasn't any life on the land, no insects in the air, or even worms in the ground. And most important of all, there weren't any plants; not a speck of green anywhere in the Ordovician. The carbon dioxide in the atmosphere was not being absorbed by plants and therefore, they were not uplifting the atmosphere with oxygen. But like with the Cambrian, it was a different story out in the seas of the Ordovician. There had been life in the seas for hundreds of millions of years and as a result, evolution had also created some real monsters.
The list of animals during the Ordovician: