The Paleozoic was the first era of the Phanerozoic eon, corresponding to the Paleozoic erathem of the Phanerozoic eonothem. It started after the Ediacaran at 538.8 ± 0.2 Ma and lasted until the beginning of the Induan age of the Triassic period of the Mesozoic era at around 251.902 ± 0.024 Ma (IUGS 2023). Paleozoic includes 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.
Occurrence[]
541–252 Ma
Definition[]
Trichophycus pedum, a marker of the base of the Paleozoic
The Global Stratotype Section and Point (GSSP) of the Paleozoic erathem as well as the Cambrian system, the Terreneuvian series, the Fortunian stage and the whole Phanerozoic eonothem was ratified in 1992. The base of the erathem is defined on the Fortune Head, the island of Newfoundland, Canada, and related to the first appearance of the ichnospecies Trichophycus pedum.[1]
Timeline and life of the Paleozoic[]
Cambrian[]
The Cambrian was a time when the first 'super-predators' evolved. Invertebrates like this Anomalocaris reigned supreme in the seas.
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.
Ordovician[]
Reconstruction of Endoceras
Ordovician was likely the most noticeable period of the Paleozoic era. Started with the extremely high temperatures (over 43 °C in the surface waters of the equatorial seas), it finished at the height of the ice age, during which the equatorial seas cooled down to 24 °C, colder than today. Primitive life forms of the Cambrian gave way to more advanced ones during the Great Ordovician Biodiversification Event (GOBE), one of the most significant biological radiations in the Phanerozoic. Endocerid cephalopods were the largest animals of the Ordovician with Endoceras reaching up to almost 6 m in shell length. At the Ordovician-Silurian boundary, the mass extinction occurred.
Silurian[]
Silurian eurypterids hunting small jawed fish. Orthocerid cephalopods can be seen in the background.
During the Silurian, massive coral reefs formed. The diversity of cephalopods increased, although their numbers decreased markedly towards the end of the period. Fish with jaws appeared and it was this period that marked the beginning of the flourishing of vertebrates. The oldest arachnids and myriapods are also known from the Silurian. It is assumed that the first insects also arose in this period. Arthropods are the first unquestionable land animals in the Earth history. The conquest of land by animals became possible due to the increase in the number of land plants that produced oxygen. However, the carbon dioxide content in the Silurian was much higher than today's levels.
Devonian[]
The first amphibians like this Ichthyostega evolved in the middle of the Paleozoic: the Devonian.
Known sometimes as the 'Age of Fishes', Devonian period 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. At the end of the Frasnian age, another great extinction happened, after which reef formation returned to its previous level only in the Mesozoic.
Carboniferous[]
Insects like Meganeura ruled the skies in the late Carboniferous.
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.
Permian[]
Dimetrodon was one of the largest land carnivores of the Early Permian, and the Paleozoic Era.
Pangaea finally formed at the dawn of the Permian. The global Carboniferous swamps disappeared due to glaciation, and in their place came the first conifers who dominated the rocky, dry climate. Sail-backed synapsids ("stem-mammals") such as Dimetrodon, Clepsydrops, and Edaphosaurus were the dominant land animals of the Cisuralian epoch.
Gorgonopsids were a group of large Permian predators.
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 synapsids and 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' occurred, killing 96% of life on Earth.