Fish, arthropods, amphibians and reptiles all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, it was dominated by various forms of organisms. Greatforests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. Towards the end of the era, large, sophisticated reptiles were dominant and the first modern plants (conifers) appeared.
The Paleozoic Era ended with the largest mass extinction in Earth's history, the Permian–Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic to recover. Recovery of life in the sea may have been much faster. -Wikipedia, Paleozoic
PURE ENERGY EXPANDED, then splintered, into a trillion galaxies whose creativity brought forth at least one planet with a four-fold mode of action: a churning lithosphere, washed by the great gyres of the hydro-sphere, evaporating into the billowing winds of the atmosphere, and all folded into the electrified intensities of the biosphere. Earth took its quan-tum of nuclear energy given by the supernova Tiamat and created a cyber-netic system that kept itself in a rich metastability, a great ball dancing at the crest of a spraying fountain of water. In the center of such rich energy, life brought forth the wonders of the eukaryotic cell, meiotic sexuality, ecosystemic communities, and the multicellular beings. A pervasive desire among early animals is to increase in size. A larger animal can escape the rule of prey. Fewer of the early predators will feed on an animal that has grown beyond the size of their toothless mouths. From the other perspective, a predator who increases in size will be able to draw ever more of the life world into its feeding patterns. When life had, through long trial and error, established a functional Argos---a viable mul-ticellular creature—such animals proliferated rapidly by entering the ad-venture of exploring the oceans at the end of the Proterozoic era. The animals grew and diversified to become the early jellyfish, sea pens, and flat worms of six hundred million years ago at the dividing time of the Proterozoic and Phanerozoic eons. All such animals entered the "vis-ible" scale, geologically speaking, overnight, and their expansions in size quickly met the upper limits inherent to cosmological dynamics. An animal that is too large will be too feeble to live vibrantly in Earth For instance, a jellyfish is one hundred thousand times—five orders of magnitude—wider than one of its constituent cells, and thus has the size I advantages for feeding on unicellular organisms. But if the jellyfish were to expand again two or more orders of magnitude, the electromagnetic bonds holding the cells together would not be strong enough to withstand even slight impacts. Its membranes would tear apart in even gentle ocean waves. Given the autopoietic shape of a jellyfish, its functioning has an optimal size. This optimal size is established partially by Earth in the sense of the dynamics of biosphere and hydrosphere, and partially by the universe in the sense of the strength of the fundamental interactions that were set into a perduring form at earliest symmetry break. The emerging animals at the start of the Phanerozoic strove to increase in size until they entered the range of their optimal existence. This range of the optimum for multicellular creatures is the mesocosm, a domain in between the microcosm of the molecules and the macrocosm of planets and galaxies, a realm with its unique dynamics. If any creature from any phylum of Earth's life were to be expanded toward the dimensions of the Milky Way, or shrunken to the dimensions of helium, the creature would perish far, far before it reached either of those other two realms. If the Flaring Forth had been even slightly different, life's mesocosm would be vastly different. In that sense, then, the mesocosm can be under-stood as a specific, quantitatively particular, possibility that had been set into the structures of the universe from the beginning. In examining an animal of the mesocosm one sees a being whose shape has been roughly hewn by the dynamics at work since the origin of time. The invention of the mesocosm is an evocation of an adventure implicit in the earliest fire of the cosmos. In cosmogenesis each fundamental breakthrough evokes a multiplicity of possibilities. In each new era, creativity explodes to populate the realm with an abundance of novelties, many of which do not survive. In the ear-liest universe the wild exotic particles were replaced by a calmer set of hadrons and leptons that became the standard particles for the rest of time. When the universe was given the opportunity to fashion galaxies, it brought forth a great display that was then sculpted down as many of the strangest and most exotic galaxies were captured and folded into the stan-dard elliptical form. When life entered the mesocosm it too exploded with new structures-- the structures of advanced animal forms. All future forms of animals are music played on the basic themes established at the crossover from the Proterozoic to the Phanerozoic, six hundred million years ago. Great ad-ventures in differentiation remained, but the most primordial creativity re-sponsible for fashioning the fundamental body plans would soon be finished. The animal phyla that survived the early catastrophe are all Earth would ever see. No new phyla would appear. All future animals would em-ploy the same structures that appeared at that time—as the jellyfish, the annelid worms, the sponges, the starfish, the snails, the sea urchins, the vertebrates, the nautiloids, the insects, the brachiopods, the crustaceans, the spiders, and a dozen, or so less prevalent forms of animal life.
THE PHANEROZOIC EON has three eras: the Paleozoic, from 570 to 245 TH million years ago; the Mesozoic, from 245 to 67 million years ago; and the Cenozoic, from 67 million years ago to the present. Each is characterized by its own biological and geological creativity. One of the first great inventions of the Paleozoic era was the hard shell. By using such minerals as phosphorus and calcium, previously naked ani-mals could protect themselves with the shells common among trilobites, clams, and snails. Most of the Paleozoic animals fed on the algae of the oceans, but heterotrophy of advanced animals took place within the meso-cosm as well. Shells did not eliminate such feeding. Responding to the challenge of such shells, nautiloids developed a beak with the power of snapping through the shell to the fleshy insides of their prey. Another kind of shell was produced by the early fishes, who developed out of the family of worms. The ostracoderms invented a bony plated ar-mor to protect themselves, and they quickly became a principal predator along the ocean bottom during the middle Paleozoic. Able to wiggle and to glide up from the ocean floor, they fed more effectively than other forms of life along the bottom and initiated a creative experiment that would require two hundred million years to complete. Ostracoderms were quick-ly crowded out by more effective predator fish. The first major advance was the jaw, enabling a fish to bite down hard. Jawed fish had a much vaster domain in which they could hunt. Later genetic mutations enabled paired fins to be added to the basic jawed fish body, enabling far greater stability in movement. These placoderms soon reached sizes of thirty feet as they soared through Paleozoic seas. A final development—fins supported by fin bones--led to the ray-finned fish, a form of animal so effective in its move. ment it proliferated through the oceans, eliminating altogether the armored form of fish that had started the era. The first heroes to venture onto land were plants. The animals dared not. This was not because of any particular difficulty with air. There were most likely already some animals who could handle air with ease. When we reflect upon the nature of the continents back then, we can speculate that to have eyes was to eliminate any courage. From the tip of the sea, one faced a lifeless, thousand-mile expanse of baked rocks and rubble and dust, barren as a moonscape. There was no living soil. There was nothing green. Hell with its truculent citizens would have been more inviting. But the ultimate obstacle to movement onto land was even more ferocious. On land Life faced an invisible enemy, a reality so pervasive and so strange and so overpowering that life remained exclusively in the oceans for ninety per. cent of Earth's history This invisible power came to be called, hundreds of millions of years later, gravitation. Gravity is an ordering principle of the universe whose effects are sus-pended for organisms in the oceans. Thus life learned enough about the electromagnetic powers to create a haven where the fierce demands of gravity could be forgotten, at least for a time; and had it not been for the ancient heroes of the Paleozoic, perhaps for all of Gaian time. Waves splashed high and smashed across the granite rocks, then slid away in a foaming betrayal of their living cargo. Plants that had mastered the three-dimensional swirl in the ocean currents now found themselves flattened and baked by the sun. How many tons of life perished into crisp green flakes that scattered across the lifeless continents? In the sleepy semi-consciousness of those plants, how many experiences of distress as they lay plastered to the rocks? Yet the genius of creativity swelled within those plants that were un-avoidably engaged with this world-encompassing enemy. There at the edges of sea, continents, and air, a new being appeared, Capaneus, a hero who invaded an alien world. Capaneus invented the wood cell and became the first terrestrial creature able to withstand the flattening power of grav-ity. Capaneus built these solid structures with vascular vessels to transport food and material through its body. Possibly Capaneus began as a semi-aquatic plant surviving at the water's edge, and then developed enough strength to endure gravity as water levels dropped back or the seas dried up. Capaneus's descendents improved their vascular transport and deep-ened their root system as they formed forests along the edges of the rivers and oceans and throughout swampy areas. These lycopod plants required the wet and darnpy areas for their reproduction. Just as with their ancestors in the oceans, lycopod sperm needed a moist world to find their way to iycopod eggs. The novelty that completed the Paleozoic plant creativity was the naked seed organism, the gymnosperm. Now trees themselves without need of a moist surface could bring the male and female gametes together to create a seed. Having fully mastered the challenges of both gravity and aridity, such gymnosperms marched across the continents to become full forests that re-dounded back and replaced the previously dominant lycopods. Just as the ray-finned fish represented the most masterful design for fish life in the ocean and became the principal marine vertebrate, so too the naked seed plants represented the Paleozoic's supreme accomplishment in bringing the mesocosm into the previously uninhabitable dry continen-tal interiors, and so became the principal form of terrestrial plant life. The last of the Paleozoic's achievements was the mastery by animals of dry land. The first animals to follow Capaneus 425 million years ago were arthropods, probably millipedes, soon to be followed by their predators. These arthropods met the challenge of land by developing an exoskeleton that could keep water within. They became, in a sense, mobile living ponds. Such insects underwent a profound proliferation as they entered and adapted to the immense number of new worlds found within the lycopod and then gymnosperm forests and swamps. Dragonflies developed wing spans of eighteen inches. Millipedes grew to eight feet in length. One scor-pion was large enough to kill and consume small vertebrate animals when they appeared later in the Paleozoic forests. By the last part of the Paleo-zoic, the insects had achieved subtle adaptations that would never be sig-nificantly improved upon, becoming enduring features of the terrestrial biosphere. Vertebrates joined the adventure onto land 370 million years ago. Some 10 million years previously, at least one branch of the fish family had developed lungs. With so much life having already invaded the land, any fish that could survive even briefly along the shores of the rivers, lakes ponds, or oceans would have found its way into a paradise of food. Not only were there trillions of insects, the vast majority of these would not be capable of recognizing the large hungry object as a predator. Having evolved in a vertebrate-free forest, the insects would have no instinctual responses stored in their DNA for protecting themselves from such preda-tion. These air-breathing fish would need only the most rudimentary locomotion. Of all the types who attempted this move, the lobed fish proved to have a slight advantage anatomically and thus prevailed as the form of vertebrate to survive on land. The descendents of the lobed fish, the amphibians, retained the ancient fish strategy of laying eggs in the water. Amphibians began their lives as fish, as tadpoles with gills, growing through their juvenile stages in the water; but then quit the seas, grew lungs, and made their way into the world of swamps and forests, reaching sizes of twenty feet in length.
-Brian Swimme and Thomas Berry, The Universe Story, p113-120
Geologists in North America use the terms “Mississippian” and “Pennsylvanian” to describe the time period between 358.9 and 298.9 million years ago. In other parts of the world, geologists use a single term and combine these two periods into the Carboniferous.
Each section needs a part on what evolutionary developments happened during that time:
The evolution of chewing, and then of predation, started an arms race that rapidly transformed ecosystems around the world.
The invention of the woody trunk must have been huge. Surely more than anything else, this has altered the surface of the world.