The Paleozoic Era The Beginning Of An Explosion Of Life Forms The Paleozoic Era is the beginning of an explosion of life forms. The CambrianExplosion marks the era with thousands of new life forms in the ancient seas. There was certainly life before the Cambrian Period. There were even many complex life forms. In late Precambrian time was a period called the Ediacaran. Ediacaran fossils are found in the Ediacaran Hills of Australia, Northwest Territories, Yukon, British Columbia, and Newfoundland in Canada. There are many different types of Ediacaran fossils. What distinguishes these fossils is that there are no hard body parts to fossilize. This makes them very rare. Generally soft tissue disintegrates long before fossilization can take place except in these few locations. The other distinguishing characteristic is that Ediacaran life forms are nothing at all like those of the Cambrian Period! Life In The Seas It is this characteristic, life in the ancient sea, which distinguishes the Paleozoic Era from all others. You see, the autotroph s (cyanobacteria) makeup didn t just add oxygen to the atmosphere. It was an entirely new sort of cell structure: one that had a cell membrane or wall (or both) that enclosed a central nucleus. Today we call this a eukaryotic cell. These new cells could now join together to do specialized tasks, the kind of specialization needed to make the tissues of plants and animals. Now species could exist that responded to the diversity of their watery environments. Some would live on the bottom sediments, burrowing with tube-shaped bodies or walking with many tiny legs. Others would live in the ocean column, developing fins for effective swimming like the pikia pictured here, a chordate from the Paleozoic Era Cambrian Period.
New Phyla Many phyla were represented in the Paleozoic Era. In fact all of the phylum in today s world were represented during the Cambrium Period. Some of those representatives including: arthropods (Trilobites were everywhere!), mollusks, Lophophorata (Brachiopods), appeared almost immediately in the Cambrian while Orthoceras-a straight-shelled mollusk-came in around the Ordovician Period), echinoderms (The flower-like crinoid thrived in seas throughout the Era.) and, eventually, fish in the Devonian Period(. All of them had specialized tissues for performing the functions of their bodies: eating, breathing, moving, and reproducing. Life Moves Onto Land Plants and animals first moved onto land in the Silurian Period. But they didn't really flourish there until the Carboniferous Period when huge forests covered the land. These forests were so dense and covered so much of the earth that oxygen was 35% of the atmosphere compared to present day levels of 21%.
Giant Insects It is this high oxygen content that is believed to be the cause of the gigantic arthropods that lived in these forests. A dragonfly called Meganeura had a wingspan 70 cm! The centipede like Arthropleura could reach a length of 1.8 meters and giant scorpions grew over 50 cm long. Of course there were an abundance of insects of sizes we would find unremarkable as well. Tetrapods The high oxygen content may have made it easier for the amphibians that also left the water during the carboniferous period. These four legged creatures called tetrapods lived at the waters edge. The tetrapods became very successful evolving many different forms some of which grew quite large over 2 meters in length! They became the dominant life forms in the lakes, rivers and swamps of the Carboniferous Period. The first reptiles showed up late in the Carboniferous Period as well but they did not play an important part during the Paleozoic Era. The Paleozoic Era Life on our planet wasn t exactly like that of today during the Paleozoic, but the similarities had arrived. Earth s miracle of life had begun and was taking hold in ancient seas of the Paleozoic. There was great diversity in the oceans and on land as well. Change is the way of life and the end of the Permian Period, the last of the Paleozoic Era brought about great changes. Mass Extinction Near the end of the Paleozoic Era was an event called the Permian mass extinction. At this time about 95% of all living things on earth became extinct! This ending made way for a new time and new life forms.
The Permian Period: The End of An Era The Permian Period is the final period of the Paleozoic Era. It began about 290 million years ago and lasted until 248 million years ago. The greatest mass extinction that has ever occurred on earth took place at the end of this 42-million-year period. Its name comes from a region of west-central Russia called Perm Oblast. This is where rocks from this time were first found. Pangea Is Now Complete For most of the Permian, life on Earth was much like it had been in the Carboniferous. Temperatures were cooler because the continent of Pangea was moving northward. Mountains were forming as the supercontinent Pangea moved. When the continent of Siberia collided into the northern part of Euramerica, Pangea was complete. The Ural Mountains were pushed up by this collision. Conditions Become Dry On Pangea Pangea was shaped like a large C. It surrounded the Tethys Sea. The rest of the Earth was covered by a huge ocean named Panthalassa. Even though the ocean covered much of the earth, Pangea was so large that the interior did not benefit from the ocean waters. Deserts were places in the center of Pangea where the temperatures changed from very cold to very hot. In some places there was rarely or never any rain. Over all the earth was dry during the Permian Period. Plants Adapt To Dry Climate The swamp land dried up and many of the plants that needed the water died out. New plants developed that were adapted to the dryer conditions. They were called gymnosperms. These plants had seeds. One of the earliest of these plants still exists today. It is called the Ginkgo. Most of the trees living during this time period were conifers. Conifers are trees with seeds in cones.
The Dry Climate Favors The Reptiles The changing climate affected how animals were evolving also. Amphibians that had depended on the swamps for a moist habitat began to die out. They were replaced by the reptiles whose bodies could live in the very dry air and the wide changes in temperature. Pelycosaurs evolved from their beginnings in the Carboniferous. These animals look like a reptile, but have skull characteristics that make them more like a mammal. The most famous of the pelycosaurs is the Dimetrodon. Like many other pelycosaurs, Dimetrodon had a large sail on its back. The sail could have been used to help keep the body temperature stable. Therapsids developed during the Permian Period also. These animals are the ancestors of mammals and share some bone structure characteristics. Some of the therapsids from the Permian period may have had fur to help them adapt to the temperature changes. Coral Reef Building The corals began to produce again in the Permian Period. After near-extinction at the end of the Devonian period, corals were now making huge reefs. Many corals did not survive the mass extinction that came with the end of the Permian. The horn corals and tabulate corals that had built many reefs in the Devonian period were all gone after the Permian. The End of The Permian Period The corals were not the only species to become extinct. The Permian Extinction was largest mass extinction that had ever occurred. No extinction since has killed so much of the life on the planet. In the seas, 90 to 95 percent of the species went extinct or were severely harmed. On land the damage was less severe, but some species, like the pelycosuars, died out completely.
Mass Extinction Theories Volcanic Activity There are many theories about the cause of this great extinction. It could have been caused by huge amounts of volcanic activity, more than any that has been experienced since written history. We know from recent volcano eruptions that large eruptions can cause the temperature to drop all around the globe. Comets and Meteors Another theory is that a comet or meteor could have hit the planet, setting off a series of events that would have caused changes to temperature and sea levels, including the formation of glaciers. Others think that the formation of a land mass as huge as Pangea upset the balance of climate that happens when the ocean waters can affect more of the land surface. No matter what the cause, the extinction event that took place at the end of the Permian Period was so important that it brought the end to the Paleozoic Era. Life on Earth would never again look as it had during the Paleozoic Era.
The Carboniferous Period: Plants Cover The Earth The Carboniferous Period of the Paleozoic Era began 354 million years ago. It lasted for about 64 million years, until 290 million years ago. The name Carboniferous came from the large amounts of carbon-bearing coal that was formed during the period. In the United States, the Carboniferous is divided into two epochs. The Mississipian Epoch is the older third and the Pennsylvanian Epoch is the more recent two-thirds. A chart or timeline of the Carboniferous and its divisions would look like this: Carboniferous Period 354 MYA (million years ago---290mya Mississippian Epoch Pennsylvanian Epoch Shifting Continents Create Mountains As Pangea Is Born The large land masses of Euramerica and Gondwana continued to move toward one another and collide during the Carboniferous Period. Collisions meant some of the land uplifted into mountains. These mountains had no plants covering them. During rainy seasons huge amounts of surface rock was washed into flood plains and deltas. Eurameica and Gondwana were working to form the large supercontinent Pangea that would be important during the next period of the Paleozoic Era. Invertebrates Contribute To The Formation of Limestone In the early part of the Carboniferous Period, the Mississippian Epoch, much of North America was covered by warm, shallow seas. The many animals living in these waters contributed their shells to the formation of
limestone. There were so many crinoids living in these waters that they make up a big part of the limestone formation. The Lophophorata There were many bryozoans living in the shallow seas of the Carboniferous Period. Bryozoans are filter feeding animals that form colonies or attach to rock surfaces. Brachiopods covered the sea floor. These bivalves look like clams, but are actually related to the bryozoans. Both are members of the phyla Lophophorata. The Trilobites The trilobite was less and less common during the early Carboniferous or Mississippian and was headed for extinction. The Fish of The Carboniferous The placoderms, or armored fish, that had ruled the Devonian seas, became extinct with the end of the Devonian period. They were replaced with fish that looked more like our modern fish. Many species of fish and sharks developed during the late Carboniferous. The Pennsylvanian Epoch In the middle and late Carboniferous Period, the land was rising up out of the waters. Some of this was because of the land masses moving toward each other and pushing the land upward, but it was also because of the thickening of the Earth s crust. Two ice sheets over the South Pole also took a large amount of water out of the oceans and the water cycle. More of the land was exposed to the air at this time. Both plants and animals had to adapt to the changing habitat. Short periods of drought brought on by the glaciers caused mass extinctions of the invertebrates that lived in the shallow seas. The shallow seas became swamps between the ocean and the dry land. Plants Put The Carbon In Carboniferous New plants developed in the warm, humid climate and swampy conditions of this period. Large trees covered with bark and huge ferns grew in the middle Carboniferous swamps. The plants gave off so much oxygen that the air had much more oxygen in it. This allowed plants and animals to reach sizes that are not known in
today s atmosphere. When the huge trees and ferns died, they fell into waters that did not have bacteria to help them decompose. These plants formed peat beds. Eventually, with the weight of layers and layers, these peat beds turned to coal. See samples of Coal Shale Fern Fossils from the Pennsylvanian Epoch for sale. Amphibians And Reptiles Land animals became more and more diverse as the land areas grew. Tetrapods were four-legged vertebrates that began to move onto the land in the late Devonian period. During the Carboniferous, more and more species of tetrapods evolved. Some were early amphibians that began their lives in the water and later moved onto land. Some were early reptiles that developed leathery skin as they moved to the parts of land that were very dry. These early reptiles also developed leathery coverings for their eggs so the insides didn t dry out while the baby inside developed.
Giant Insects Insects also grew well in the humid and high-oxygen conditions. One of the largest was the Meganeura. This large ancestor of the dragonfly had a wingspan of 60 to 75 cm. Another large arthropod lived on the floor of the Carboniferous forests. The Arthropleura was a giant millipede that could grow to more than one and a half meters long. They sometimes had as many as 30 pairs of legs! The End of The Carboniferous Period The end of the Carboniferous period is marked by global climate changes due to the glaciers that covered the South Pole. The mass extinctions that mark the end of other geologic periods were not present, yet many species did go extinct during this time. The marine environments were most affected by these climate changes, so the extinctions were mostly invertebrates that spent their lives in the seas. Horn corals, trilobites and some forms of crinoids were on the road to extinction that would come in the next period, Below is a video of what it may have been like in the Carboniferous Period. It is taken from the BBC's Walking with Monsters, First Life, and Prehistoric Park. It is about 3 minutes long.
The Devonian Period: The Age of Fish The Devonian Period of the Paleozoic Era lasted from 417 million years ago to 354 million years ago. It is named for Devon, England where the old red sandstone of the Devonian was first studied. The Continents of The Devonian During the Devonian there were important changes in the land masses on the globe. North America and Europe had collided forming a large continent called Euramerica. This caused the formation of the Appalachian Mountain Range. The other large land mass was Gondwana. It was made up of South America, Africa, Antarctica, India and Australia. These two large land masses lay close to one another near the equator. The two continents were moving toward each other throughout the Devonian Period. The waterway between the two continents covered a subduction zone. This is an area where one plate is moving underneath the other. Eventually this would mean that the two continents would collide to form the supercontinent Pangea in the Permian Period. That event is more than 64 million years later. Plants Cover The Land Laying so close to the equator meant that the climate of the Devonian was warm. The warm temperatures made life on land particularly good for the plants. They developed vascular tissues to carry water and food through roots and leaves. The most important development was the seed. Now plants were not dependent on the presence of water for reproduction and they could move further inland. Ferns and the first trees began to cover the land. Insects and Other Animals Find Homes On Land The plant-covered lands made a good home for the first wingless insects and spiders. Even a primitive vertebrate, the tetrapod or four-footed vertebrate, developed the ability to live outside the water and move on land.
The Age of Fishes The Devonian is known as the Age of Fishes. It is famous for the thousands of species of fish that developed in Devonian seas. We know this because of the fish fossils found in Devonian rocks. When fish first started to develop, they had no jaws and the support structure was made of cartilage. This material doesn t fossilize well, so the earliest fossils were of fish whose outside skin was protected by scales and plates made of boney tissue. These fish were called Ostracoderms. Their name means shell-skins. These animals appear in rock from the late Silurian and early Devonian periods. Fish with Jaws The next development was the fish with jaws, gills and paired fins. The Placoderms were the first fish to have all three of these characteristics. They still had the shell skin of the Ostracoderms, but it mainly covered the head and neck area. The largest of the Placoderms was the Dunkleosteus. It was a huge predator in the Devonian seas. It could be as long as 10 meters. Instead of teeth, it had large boney plates that stuck down in the front of its mouth opening. The powerful jaws were deadly to other fish, sharks and even other Dunkleosteus. Ancient Sharks Sharks, or Chondricthyes, developed during the Devonian also. Sharks are thought to be descendents of the large Placoderms, but they lost the ability to form the boney armor on the outside of the body and were unable to form bones on the inside also. Their body is supported by cartilage. Because of the skeletons of cartilage, very little fossil evidence is available. They did leave behind their teeth. Much of the information we have about ancient sharks comes from the many different types of fossil teeth that have been found. Sharks first appear during the middle of this period. The Bony Fish; Osteichthyes The bony fish appear during the middle Devonian Period. The first of these are the lobe-fins. These fish have pairs of fins with fleshy lobes at the base and more typical fin membranes at the ends. The lobes contain jointed bones. These lobe-fins are thought to have evolved into legs and eventually into amphibians that spend their lives both in and out of the water.
The coelacanth is a lobe-fin fish that developed during the Devonian. For years it was thought to have gone extinct at the end of the Mesozoic Era along with the dinosaurs, but in 1938 a living coelacanth was caught. Since then coelacanths have been seen from time to time in the Indian Ocean. The Lung Fish The Dipterus was a lungfish that developed at this time. In many ways it looked like the lobe-fins with bony flesh at the base of its fins. But the Dipterus had lung sacks branching off of its throat that got air from the gills. During the Devonian Period, there were huge swings of floods and drought. During drought times, when lakes turned into ponds, the plants used all the oxygen in the little water that remained. A Dipterus that was stranded in such a pool could stick its head out of the water and get the air it needed to stay alive. The Reef Builders The reef building work of the sponges and corals went on through the Paleozoic Era. They built some of the largest reefs in the world. Invertebrates grew well in Devonian seas too, so many new species developed. The ammonite is one of these. Mass Extinction Ends The Period Species had begun to branch out and include both land and water habitats. The Devonian Period ended with a mass extinction. The Devonian extinction hurt the water habits much more than those on land. The sponges and corals were the most affected. No major reef building happened again for thousands of years.
The Silurian Period: Plants Move Onto Land The Silurian Period follows the Ordovician Period in the Paleozoic Era. It began around 443 million years ago and lasted for 26 million years. Like the periods that have come before, it is named for an ancient Celtic tribe that lived in Wales where the geologic evidence was found. Silurian Climate The climate was much warmer during the Silurian Period. This caused the glaciers to melt and the seas to rise. Even though the sea level was rising, there were places where the land was slowly rising as well. This was due to mountain building as the continental plates collided. In these places the seas moved away from the coasts or evaporated from the shallow areas. This left salt deposits. Plants that had lived in the coastal water had to adapt to life on land or die. Continents Gondwana was still located in the southern hemisphere, but it stretched from the Equator, where modern-day Australia was located, to the South Pole, where modern South America was located. The tectonic plate that contained North America was moving toward the southeast. By the end of this period it would collide with another plate and form a mountain range. Most of North America was covered by shallow seas during this time. Life in the Seas of The Silurian Period Of course, the warm shallow seas made good conditions for marine life to grow. The species that survived the mass extinction at the end of the Ordovician Period branched out and developed new variations. Among these survivors were the nautiloids, brachiopods, bryozoans and crinoids. Crinoids were filter feeding echinoderms that grew on long stalks attached to the sea bottom. They looked like flowers floating in the water. The long feathery arms caught the food for the crinoid.
51Save The Rise of The Eurypterids Cephalopods were smaller and there were fewer of them than during the Ordovician Period. The Eurypterids or Sea Scorpions, made their first appearance in the Ordovician Period. In the Silurian they became the dominant predator. Eurypterids were arthropods. Arthropods have an exoskeleton and jointed legs. Crabs, insects, and spiders are all arthropods. One of the Sea Scorpions of the Silurian grew to be ten feet long. It was a huge predator that had large claws for snagging its prey. Coral; The New Reef Builders The new life in the Silurian Period was the coral reef. Tabulate corals and rugose corals formed these reefs in the Silurian rocks. Tabulate corals lived in colonies that formed chains. The chains sometimes looked like clumps of organ pipes. Rugose corals are often called horn corals because their shape looks like the horn of a bull. The tentacles of the animal reached out the top of the cup. The huge reefs made great hiding places for the new animal that lived in the ocean: the fish. Fish Gain Importance During The Silurian Fish were a growing in importance during the Silurian Period. At the beginning, most of the fish were jawless. These were some of the earliest vertebrates, animals with a soft cartilage backbone. By the end of the Silurian many fish with jaws and real bones were swimming in the waters. These animals would soon rule the seas! Life On Land Mosses and other primitive plants grew over the land near the water s edge. They continued the work of the lichen turning the rock into soil. There are a few fossils from the end of the Silurian Period that show us early insects lived among these mosses and made their own colonies. The Cooksonia Invent Vascular Tissue The soil made by the lichens grew strange plants called Cooksonia. These plants had stems, but no real leaves. Some Cooksonia had special tissues for carrying water and nutrients upward to the branching parts of the plant. This vascular tissue is common in modern plants, but was a first during the Silurian Period.