The Paleozoic Era
The Paleozoic Era was the era prior to the Mesozoic Era, and the first era of the Phanerozoic Eon. It is comprised of six periods; the Cambrian, Ordovician, Silurian, Devonian, Carboniferous*, and Permian periods. The era is split into the early Paleozoic (Cambrian to Silurian), and the late Paleozoic (Devonian to Permian) The Paleozoic saw the first fishes, amphibians, and reptiles, who evolved from each other in the order listed.
At the beginning the Cambrian Period, life mostly consisted of small single celled and multi-cellular life forms, but within twenty Ma, life had diversified into many unique forms, the two most notable being the arthropods and the vertebrates (existing only as fishes at the time). Other types of life did exist, however, including animals such as sponges and gastropods. The famous arthropods known as trilobites evolved, but were dwarfed by larger predatory arthropods, like Anomalocaris. The Proterozoic continent known as Pannotia began to split apart. Towards the end of this time, glaciation occurred, killing most land life.
Known sometimes as the 'Age of Fishes', this time is famous for the mass diversification of fishes. Jawless, yet complex fishes evolved, as did jawed fishes, such as Dunkleosteus. Vascular plants and trees evolved towards the end of this time, as did amphibians, but the fishes remained at the top of the food chain, with large fish such as Hyneria regularly feeding on their more advanced amphibian cousins.
During the carboniferous, land life had grew much more common, and reptiles evolved from amphibians. Average temperatures worldwide were very high, turning the land from a lightly-forested wasteland into a huge global swamp. Trees became very common, and, as decomposers had not yet evolved, fallen trees simply became compressed into the ground, creating huge coal deposits. Due to the high oxygen content, land invertebrates grew to huge sizes, with arthropods such as Pulmonoscorpius and Arthropleura growing many times larger than their modern equivalents. seventy centimetre wide griffinflies soared above the canopy as amniotic amphibians fed in inland pools.
Pangaea formed at the dawn of this period. Sail-backed stem mammals such as Dimetrodon, Clepsydrops, and Edaphosaurus were the dominant land animals of the age. The global carboniferous swamps disappeared due to glaciation, and in their place came the first conifers who dominated the rocky, dry climate.
The climate grew drier, and even places as far north as Siberia became hot deserts. Large carnivores such as the Gorgonopsids struggled to survive by eating other 'mammal-like reptiles' such as Scutosaurus. Eventually, the huge animals of the Permian succumbed to the incredible temperatures and a lack of precipitation. An event known as the 'Great Dying' occured, killing 96% of life on Earth.