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76-461: The Boreal Sea was a Mesozoic -era seaway that lay along the northern border of Laurasia . This palaeogeography article is a stub . You can help Misplaced Pages by expanding it . Mesozoic The Mesozoic Era is the era of Earth's geological history , lasting from about 252 to 66 million years ago , comprising the Triassic , Jurassic and Cretaceous Periods . It

152-483: A boom of dinosaurian evolution on land as the continents began to separate from each other (Nyasasaurus from 243 to 210 million years ago, approximately 235–30 ma, some of them separated into Sauropodomorphs, Theropods and Herrerasaurids), as well as the first pterosaurs . During the Late Triassic, some advanced cynodonts gave rise to the first Mammaliaformes . All this climatic change, however, resulted in

228-622: A cataclysm known as " The Great Dying ", the third and most severe Phanerozoic mass extinction. The early Cambrian climate was probably moderate at first, becoming warmer over the course of the Cambrian, as the second-greatest sustained sea level rise in the Phanerozoic got underway. However, as if to offset this trend, Gondwana moved south, so that, in Ordovician time, most of West Gondwana (Africa and South America) lay directly over

304-594: A coating. This contrasts with the earth's current flora, in which the dominant land plants in terms of number of species are angiosperms . The earliest members of the genus Ginkgo first appeared during the Middle Jurassic. This genus is represented today by a single species, Ginkgo biloba . Modern conifer groups began to radiate during the Jurassic. Bennettitales , an extinct group of gymnosperms with foliage superficially resembling that of cycads gained

380-600: A decline in diversity of sauropods, stegosaurs, and other high-browsing groups, with sauropods particularly scarce in North America. Some island-hopping dinosaurs, such as Eustreptospondylus , evolved to cope with the coastal shallows and small islands of ancient Europe. Other dinosaurs rose up to fill the empty space that the Jurassic-Cretaceous extinction left behind, such as Carcharodontosaurus and Spinosaurus . Seasons came back into effect and

456-477: A few million years before the Triassic–Jurassic extinction event. Sea levels began to rise during the Jurassic, probably caused by an increase in seafloor spreading . The formation of new crust beneath the surface displaced ocean waters by as much as 200 m (656 ft) above today's sea level, flooding coastal areas. Furthermore, Pangaea began to rift into smaller divisions, creating new shoreline around

532-445: A foothold on land. These early plants were the forerunners of all plant life on land. During this time, there were four continents: Gondwana (Africa, South America, Australia, Antarctica, Siberia), Laurentia (North America), Baltica (Northern Europe), and Avalonia (Western Europe). The recent rise in sea levels allowed many new species to thrive in water. The Devonian spanned from 419–359 million years ago. Also known as "The Age of

608-483: A global distribution during the Late Triassic, and represented one of the most common groups of Mesozoic seed plants. Flowering plants radiated during the early Cretaceous, first in the tropics , but the even temperature gradient allowed them to spread toward the poles throughout the period. By the end of the Cretaceous, angiosperms dominated tree floras in many areas, although some evidence suggests that biomass

684-671: A large die-out known as the Triassic–Jurassic extinction event, in which many archosaurs (excluding pterosaurs, dinosaurs and crocodylomorphs ), most synapsids , and almost all large amphibians became extinct, as well as 34% of marine life, in the Earth's fourth mass extinction event. The cause is debatable; flood basalt eruptions at the Central Atlantic magmatic province is cited as one possible cause. The Jurassic ranges from 200 million years to 145 million years ago and features three major epochs: The Early Jurassic,

760-435: A variety of niches, beginning in the mid-Triassic 4 million to 6 million years after the extinction, and not fully proliferated until 30 million years after the extinction. Animal life was then dominated by various archosaurs: dinosaurs , pterosaurs, and aquatic reptiles such as ichthyosaurs, plesiosaurs, and mosasaurs . The climatic changes of the late Jurassic and Cretaceous favored further adaptive radiation. The Jurassic

836-660: Is characterized by the dominance of gymnosperms such as cycads , ginkgoaceae and araucarian conifers, and of archosaurian reptiles such as the dinosaurs ; a hot greenhouse climate; and the tectonic break-up of Pangaea . The Mesozoic is the middle of the three eras since complex life evolved : the Paleozoic , the Mesozoic, and the Cenozoic . The era began in the wake of the Permian–Triassic extinction event ,

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912-611: Is considered the first Phanerozoic mass extinction event, and the second deadliest. The Silurian spanned from 444–419 million years ago. The Silurian saw the rejuvenation of life as the Earth recovered from the previous glaciation. This period saw the mass evolution of fish, as jawless fish became more numerous, jawed fish evolved, and the first freshwater fish evolved, though arthropods, such as sea scorpions , were still apex predators . Fully terrestrial life evolved, including early arachnids, fungi, and centipedes. The evolution of vascular plants ( Cooksonia ) allowed plants to gain

988-546: Is the first period of the Paleozoic Era of the Phanerozoic. The Cambrian marked a boom in evolution in an event known as the Cambrian explosion in which the largest number of creatures evolved in any single period of the history of the Earth. Creatures like algae evolved, but the most ubiquitous of that period were the armored arthropods, like trilobites. Almost all marine phyla evolved in this period. During this time,

1064-575: Is the sudden appearance of nearly all of the invertebrate animal phyla in great abundance at the beginning of the Cambrian. The first vertebrates appeared in the form of primitive fish, which greatly diversified in the Silurian and Devonian Periods. The first animals to venture onto dry land were the arthropods. Some fish had lungs, and powerful bony fins that in the late Devonian, 367.5 million years ago, allowed them to crawl onto land. The bones in their fins eventually evolved into legs and they became

1140-537: Is thought that a large meteor smashed into earth 66 million years ago, creating the Chicxulub Crater in an event known as the K-Pg Extinction (formerly K-T), the fifth and most recent mass extinction event, in which 75% of life became extinct, including all non-avian dinosaurs. Compared to the vigorous convergent plate mountain-building of the late Paleozoic, Mesozoic tectonic deformation

1216-473: The Cambrian explosion , in which most modern phyla first appeared. Arthropods , molluscs , fish , amphibians , reptiles , and synapsids all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America . Towards

1292-531: The Carboniferous Rainforest Collapse . Gondwana was glaciated as much of it was situated around the south pole. The Permian spanned from 299–252 million years ago and was the last period of the Paleozoic Era. At the beginning of this period, all continents joined together to form the supercontinent Pangaea, which was encircled by one ocean called Panthalassa . The land mass was very dry during this time, with harsh seasons, as

1368-645: The Early Palaeozoic Icehouse , culminating in the Hirnantian glaciation, 445  million years ago at the end of the Ordovician. The middle Paleozoic was a time of considerable stability. Sea levels had dropped coincident with the ice age, but slowly recovered over the course of the Silurian and Devonian. The slow merger of Baltica and Laurentia, and the northward movement of bits and pieces of Gondwana created numerous new regions of relatively warm, shallow sea floor. As plants took hold on

1444-648: The Greek prefix meso- ( μεσο- 'between') and zōon ( ζῷον 'animal, living being'). In this way, the Mesozoic is comparable to the Cenozoic ( lit.   ' new life ' ) and Paleozoic ('old life') eras as well as the Proterozoic ('earlier life') Eon. The Mesozoic Era was originally described as the "secondary" era, following the "primary" ( Paleozoic ), and preceding the Tertiary . Following

1520-711: The Indian subcontinent , which collided with the Asian plate during the Cenozoic, giving rise to the Himalayas . The Triassic was generally dry, a trend that began in the late Carboniferous , and highly seasonal, especially in the interior of Pangaea. Low sea levels may have also exacerbated temperature extremes. With its high specific heat capacity , water acts as a temperature-stabilizing heat reservoir, and land areas near large bodies of water—especially oceans—experience less variation in temperature. Because much of Pangaea's land

1596-586: The International Commission on Stratigraphy (ICS) to use trace fossils as an indicator of complex life. Unlike later in the fossil record, Cambrian trace fossils are preserved in a wide range of sediments and environments, which aids correlation between different sites around the world. Trace fossils reflect the complexity of the body plan of the organism that made them. Ediacaran trace fossils are simple, sub-horizontal feeding traces. As more complex organisms evolved, their more complex behaviour

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1672-561: The Permian Period allowed for the radiation of many new lifeforms. In particular, the extinction of the large herbivorous pareiasaurs and carnivorous gorgonopsians left those ecological niches empty. Some were filled by the surviving cynodonts and dicynodonts , the latter of which subsequently became extinct. Recent research indicates that it took much longer for the reestablishment of complex ecosystems with high biodiversity, complex food webs, and specialized animals in

1748-571: The South Pole . The early Paleozoic climate was strongly zonal, with the result that the "climate", in an abstract sense, became warmer, but the living space of most organisms of the time – the continental shelf marine environment – became steadily colder. However, Baltica (Northern Europe and Russia) and Laurentia (eastern North America and Greenland) remained in the tropical zone, while China and Australia lay in waters which were at least temperate. The early Paleozoic ended, rather abruptly, with

1824-458: The Atlantic seaway, which has grown continually larger until today. The further separation of the continents gave opportunity for the diversification of new dinosaurs. The Cretaceous is the longest period of the Mesozoic, but has only two epochs: Early and Late Cretaceous. The Early Cretaceous spans from 145 to 100 million years ago. The Early Cretaceous saw the expansion of seaways and

1900-434: The Cambrian and Ordovician periods. It was redefined by John Phillips (1800–1874) in 1840 to cover the Cambrian to Permian periods. It is derived from the Greek palaiós (παλαιός, "old") and zōḗ (ζωή, "life") meaning "ancient life". The Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earth's history, known as

1976-778: The Cretaceous–Paleogene extinction event. Approximately 50% of all genera became extinct, including all of the non- avian dinosaurs. The Triassic ranges roughly from 252 million to 201 million years ago, preceding the Jurassic Period. The period is bracketed between the Permian–Triassic extinction event and the Triassic–Jurassic extinction event , two of the " big five ", and it is divided into three major epochs: Early, Middle, and Late Triassic. The Early Triassic, about 252 to 247 million years ago,

2052-648: The Fish", the Devonian featured a huge diversification of fish, including armored fish like Dunkleosteus and lobe-finned fish which eventually evolved into the first tetrapods. On land, plant groups diversified rapidly in an event known as the Devonian explosion when plants made lignin , leading to taller growth and vascular tissue; the first trees and seeds evolved. These new habitats led to greater arthropod diversification. The first amphibians appeared and fish occupied

2128-545: The Jurassic, having evolved from a branch of theropod dinosaurs, then true toothless birds appeared in the Cretaceous. The first mammals also appeared during the Mesozoic, but would remain small—less than 15 kg (33 lb)—until the Cenozoic. Flowering plants appeared in the Early Cretaceous and would rapidly diversify through the end of the era, replacing conifers and other gymnosperms ( sensu lato ), such as ginkgoales , cycads and bennettitales as

2204-465: The Late Cretaceous declined for poorly understood reasons, though this might be due to tendencies of the fossil record, as their diversity seems to be much higher than previously thought. Birds became increasingly common and diversified into a variety of enantiornithe and ornithurine forms. Though mostly small, marine hesperornithes became relatively large and flightless, adapted to life in

2280-469: The Mesozoic was varied, alternating between warming and cooling periods. Overall, however, the Earth was hotter than it is today. Dinosaurs first appeared in the Mid-Triassic, and became the dominant terrestrial vertebrates in the Late Triassic or Early Jurassic, occupying this position for about 150 or 135 million years until their demise at the end of the Cretaceous. Archaic birds appeared in

2356-610: The Middle Carboniferous). An important evolutionary development of the time was the evolution of amniotic eggs , which allowed amphibians to move farther inland and remain the dominant vertebrates for the duration of this period. Also, the first reptiles and synapsids evolved in the swamps. Throughout the Carboniferous, there was a cooling trend, which led to the Permo-Carboniferous glaciation or

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2432-561: The Middle Jurassic, and the Late Jurassic. The Early Jurassic spans from 200 to 175 million years ago. The climate was tropical and much more humid than the Triassic, as a result of the large seas appearing between the land masses. In the oceans, plesiosaurs , ichthyosaurs and ammonites were abundant. On land, dinosaurs and other archosaurs staked their claim as the dominant race, with theropods such as Dilophosaurus at

2508-573: The Palaeozoic had very few facultatively motile animals that could easily adjust to disturbance, with such creatures composing 1% of its assemblages in contrast to 50% in Cenozoic faunal assemblages. Non-motile animals untethered to the substrate, extremely rare in the Cenozoic, were abundant in the Palaeozoic. Palaeozoic phytoplankton overall were both nutrient-poor themselves and adapted to nutrient-poor environmental conditions. This phytoplankton nutrient poverty has been cited as an explanation for

2584-571: The Paleozoic, the Mesozoic extended roughly 186 million years, from 251.902 to 66 million years ago when the Cenozoic Era began. This time frame is separated into three geologic periods . From oldest to youngest: The lower boundary of the Mesozoic is set by the Permian–Triassic extinction event , during which it has been estimated that up to 90-96% of marine species became extinct although those approximations have been brought into question with some paleontologists estimating

2660-457: The Phanerozoic, Paleozoic and Cambrian is dated at 538.8+/-0.2 Ma and now lies below both the first appearance of trilobites and SSF. The boundary between the Paleozoic and Mesozoic eras and the Permian and Triassic periods is marked by the first occurrence of the conodont Hindeodus parvus . This is the first biostratigraphic event found worldwide that is associated with the beginning of

2736-529: The Silurian Period, about 420 million years ago, when they began to transition onto dry land. Terrestrial flora reached its climax in the Carboniferous, when towering lycopsid rainforests dominated the tropical belt of Euramerica . Climate change caused the Carboniferous Rainforest Collapse which fragmented this habitat, diminishing the diversity of plant life in the late Carboniferous and Permian periods. A noteworthy feature of Paleozoic life

2812-474: The Tethys Ocean. Temperatures continued to increase, then began to stabilize. Humidity also increased with the proximity of water, and deserts retreated. The climate of the Cretaceous is less certain and more widely disputed. Probably, higher levels of carbon dioxide in the atmosphere are thought to have almost eliminated the north–south temperature gradient : temperatures were about the same across

2888-602: The actual numbers as low as 81%. It is also known as the "Great Dying" because it is considered the largest mass extinction in the Earth's history. The upper boundary of the Mesozoic is set at the Cretaceous–Paleogene extinction event (or K–Pg extinction event ), which may have been caused by an asteroid impactor that created Chicxulub Crater on the Yucatán Peninsula . Towards the Late Cretaceous, large volcanic eruptions are also believed to have contributed to

2964-466: The beginnings of the breakup of Pangaea and the opening of the Tethys Ocean . Ecosystems had recovered from the Permian extinction. Algae, sponge, corals, and crustaceans all had recovered, and new aquatic reptiles evolved, such as ichthyosaurs and nothosaurs . On land, pine forests flourished, as did groups of insects such as mosquitoes and fruit flies. Reptiles began to get bigger and bigger, and

3040-511: The climate of the interior of Pangaea was not regulated by large bodies of water. Diapsids and synapsids flourished in the new dry climate. Creatures such as Dimetrodon and Edaphosaurus ruled the new continent. The first conifers evolved, and dominated the terrestrial landscape. Near the end of the Permian, however, Pangaea grew drier. The interior was desert, and new taxa such as Scutosaurus and Gorgonopsids filled it. Eventually they disappeared, along with 95% of all life on Earth, in

3116-561: The continental margins, oxygen levels increased and carbon dioxide dropped, although much less dramatically. The north–south temperature gradient also seems to have moderated, or metazoan life simply became hardier, or both. At any event, the far southern continental margins of Antarctica and West Gondwana became increasingly less barren. The Devonian ended with a series of turnover pulses which killed off much of middle Paleozoic vertebrate life, without noticeably reducing species diversity overall. There are many unanswered questions about

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3192-431: The current level (about 21%) throughout the Mesozoic, some concluding they were lower in the Triassic and part of the Jurassic but higher in the Cretaceous, and some concluding they were higher throughout most or all of the Triassic, Jurassic and Cretaceous. The dominant land plant species of the time were gymnosperms , which are vascular, cone-bearing, non-flowering plants such as conifers that produce seeds without

3268-416: The dawn of the Mesozoic, ocean plankton communities transitioned from ones dominated by green archaeplastidans to ones dominated by endosymbiotic algae with red-algal-derived plastids. This transition is speculated to have been caused by an increasing paucity of many trace metals in the Mesozoic ocean. Paleozoic The name Paleozoic was first used by Adam Sedgwick (1785–1873) in 1838 to describe

3344-457: The dominant group of plants. The phrase "Age of Reptiles" was introduced by the 19th century paleontologist Gideon Mantell who viewed it as dominated by diapsids such as Iguanodon , Megalosaurus , Plesiosaurus , and Pterodactylus . The current name was proposed in 1840 by the British geologist John Phillips (1800–1874). "Mesozoic" literally means 'middle life', deriving from

3420-605: The dramatic rifting of the supercontinent Pangaea, which gradually split into a northern continent, Laurasia , and a southern continent, Gondwana . This created the passive continental margin that characterizes most of the Atlantic coastline (such as along the U.S. East Coast ) today. By the end of the era, the continents had rifted into nearly their present forms, though not their present positions. Laurasia became North America and Eurasia , while Gondwana split into South America , Africa , Australia , Antarctica and

3496-507: The empty continent of Gondwana. By the end of the Ordovician, Gondwana was at the south pole, early North America had collided with Europe, closing the intervening ocean. Glaciation of Africa resulted in a major drop in sea level, killing off all life that had established along coastal Gondwana. Glaciation may have caused the Ordovician–Silurian extinction events , in which 60% of marine invertebrates and 25% of families became extinct, and

3572-560: The end of the Permian period. In late middle Permian the pareiasaurs originated, successful herbivores and the only sauropsids that could reach sizes comparable to some of the largest synapsids. The Palaeozoic marine fauna was notably lacking in predators relative to the present day. Predators made up about 4% of the fauna in Palaeozoic assemblages while making up 17% of temperate Cenozoic assemblages and 31% of tropical ones. Infaunal animals made up 4% of soft substrate Palaeozoic communities but about 47% of Cenozoic communities. Additionally,

3648-538: The end of the era, large, sophisticated synapsids and diapsids were dominant and the first modern plants ( conifers ) appeared. The Paleozoic Era ended with the largest extinction event of the Phanerozoic Eon , 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 Era to recover. Recovery of life in

3724-467: The fern prairies, chased by many new predators such as Allosaurus . Conifer forests made up a large portion of the forests. In the oceans, plesiosaurs were quite common, and ichthyosaurs flourished. This epoch was the peak of the reptiles. The Late Jurassic spans from 163 to 145 million years ago. During this epoch, the first avialans , such as Archaeopteryx , evolved from small coelurosaurian dinosaurs. The increase in sea levels opened up

3800-467: The first crocodilians and dinosaurs evolved, which sparked competition with the large amphibians that had previously ruled the freshwater world, respectively mammal-like reptiles on land. Following the bloom of the Middle Triassic, the Late Triassic, from 237 to 201 million years ago, featured frequent heat spells and moderate precipitation (10–20 inches per year). The recent warming led to

3876-461: The first tetrapods, 390  million years ago , and began to develop lungs. Amphibians were the dominant tetrapods until the mid-Carboniferous, when climate change greatly reduced their diversity, allowing amniotes to take over. Amniotes would split into two clades shortly after their origin in the Carboniferous; the synapsids, which was the dominant group, and the sauropsids . The synapsids continued to prosper and increase in number and variety till

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3952-487: The food web. In the oceans, mosasaurs ruled, filling the role of the ichthyosaurs, which, after declining, had disappeared in the Cenomanian-Turonian boundary event . Though pliosaurs had gone extinct in the same event, long-necked plesiosaurs such as Elasmosaurus continued to thrive. Flowering plants, possibly appearing as far back as the Triassic, became truly dominant for the first time. Pterosaurs in

4028-432: The fossil record. The Late Cretaceous spans from 100 to 66 million years ago. The Late Cretaceous featured a cooling trend that would continue in the Cenozoic Era. Eventually, tropics were restricted to the equator and areas beyond the tropic lines experienced extreme seasonal changes in weather. Dinosaurs still thrived, as new taxa such as Tyrannosaurus , Ankylosaurus , Triceratops and hadrosaurs dominated

4104-406: The largest mass extinction in Earth's history, and ended with the Cretaceous–Paleogene extinction event , another mass extinction whose victims included the non-avian dinosaurs , pterosaurs , mosasaurs , and plesiosaurs . The Mesozoic was a time of significant tectonic, climatic, and evolutionary activity. The supercontinent Pangaea began to break apart into separate landmasses. The climate of

4180-548: The late Paleozoic. The Mississippian (early Carboniferous Period) began with a spike in atmospheric oxygen, while carbon dioxide plummeted to new lows. This destabilized the climate and led to one, and perhaps two, ice ages during the Carboniferous. These were far more severe than the brief Late Ordovician ice age; but, this time, the effects on world biota were inconsequential. By the Cisuralian Epoch, both oxygen and carbon dioxide had recovered to more normal levels. On

4256-557: The mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subducting plate uplifted eastern Australia . By the late Paleozoic, continental collisions formed the supercontinent of Pangaea and created great mountain chains, including the Appalachians , Caledonides , Ural Mountains , and mountains of Tasmania . The Cambrian spanned from 539–485 million years ago and

4332-459: The open sea. Metatherians and primitive eutherian also became common and even produced large and specialised genera such as Didelphodon and Schowalteria . Still, the dominant mammals were multituberculates, cimolodonts in the north and gondwanatheres in the south. At the end of the Cretaceous, the Deccan traps and other volcanic eruptions were poisoning the atmosphere. As this continued, it

4408-520: The other hand, the assembly of Pangaea created huge arid inland areas subject to temperature extremes. The Lopingian Epoch is associated with falling sea levels, increased carbon dioxide and general climatic deterioration, culminating in the devastation of the Permian extinction. While macroscopic plant life appeared early in the Paleozoic Era and possibly late in the Neoproterozoic Era of the earlier eon, plants mostly remained aquatic until

4484-437: The planet, and about 10° C higher than today. The circulation of oxygen to the deep ocean may also have been disrupted, preventing the decomposition of large volumes of organic matter, which was eventually deposited as " black shale ". Different studies have come to different conclusions about the amount of oxygen in the atmosphere during different parts of the Mesozoic, with some concluding oxygen levels were lower than

4560-641: The poles got seasonally colder, but some dinosaurs still inhabited the polar forests year round, such as Leaellynasaura and Muttaburrasaurus . The poles were too cold for crocodiles, and became the last stronghold for large amphibians such as Koolasuchus . Pterosaurs got larger as genera such as Tapejara and Ornithocheirus evolved. Mammals continued to expand their range: eutriconodonts produced fairly large, wolverine -like predators such as Repenomamus and Gobiconodon , early therians began to expand into metatherians and eutherians , and cimolodont multituberculates went on to become common in

4636-519: The presence of trilobite -dominated fauna. Since then evidence of complex life in older rock sequences has increased and by the second half of the 20th century, the first appearance of small shelly fauna (SSF), also known as early skeletal fossils, were considered markers for the base of the Paleozoic. However, whilst SSF are well preserved in carbonate sediments, the majority of Ediacaran to Cambrian rock sequences are composed of siliciclastic rocks where skeletal fossils are rarely preserved. This led

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4712-610: The recovery following the end- Permian mass extinctions and environmental changes. In non-marine strata, the equivalent level is marked by the disappearance of the Permian Dicynodon tetrapods . This means events previously considered to mark the Permian-Triassic boundary, such as the eruption of the Siberian Traps flood basalts , the onset of greenhouse climate, ocean anoxia and acidification and

4788-423: The resulting mass extinction are now regarded as being of latest Permian in age. The GSSP is near Meishan , Zhejiang Province, southern China. Radiometric dating of volcanic clay layers just above and below the boundary confine its age to a narrow range of 251.902+/-0.024 Ma. The beginning of the Paleozoic Era witnessed the breakup of the supercontinent of Pannotia and ended while the supercontinent Pangaea

4864-518: The sea may have been much faster. The base of the Paleozoic is one of the major divisions in geological time representing the divide between the Proterozoic and Phanerozoic eons, the Paleozoic and Neoproterozoic eras and the Ediacaran and Cambrian periods. When Adam Sedgwick named the Paleozoic in 1835, he defined the base as the first appearance of complex life in the rock record as shown by

4940-479: The short, but apparently severe, late Ordovician ice age. This cold spell caused the second-greatest mass extinction of the Phanerozoic Eon. Over time, the warmer weather moved into the Paleozoic Era. The Ordovician and Silurian were warm greenhouse periods, with the highest sea levels of the Paleozoic (200 m above today's); the warm climate was interrupted only by a 30 million year cool period,

5016-456: The supercontinent Pannotia begins to break up, most of which later became the supercontinent Gondwana. The Ordovician spanned from 485–444 million years ago. The Ordovician was a time in Earth's history in which many of the biological classes still prevalent today evolved, such as primitive fish, cephalopods, and coral. The most common forms of life, however, were trilobites, snails and shellfish. The first arthropods went ashore to colonize

5092-554: The top of the food chain. Earth's second Phanerozoic mass extinction event (a group of several smaller extinction events), the Late Devonian extinction , ended 70% of existing species. The Carboniferous is named after the large coal deposits laid down during the period. It spanned from 359–299 million years ago. During this time, average global temperatures were exceedingly high; the early Carboniferous averaged at about 20 degrees Celsius (but cooled to 10 °C during

5168-506: The top of the food chain. The first true crocodiles evolved, pushing the large amphibians to near extinction. All-in-all, archosaurs rose to rule the world. Meanwhile, the first true mammals evolved, remaining relatively small, but spreading widely; the Jurassic Castorocauda , for example, had adaptations for swimming, digging and catching fish. Fruitafossor , from the late Jurassic Period about 150 million years ago,

5244-531: Was about the size of a chipmunk, and its teeth, forelimbs and back suggest that it dug open the nests of social insects (probably termites , as ants had not yet appeared) ; Volaticotherium was able to glide for short distances, such as modern flying squirrels . The first multituberculates such as Rugosodon evolved. The Middle Jurassic spans from 175 to 163 million years ago. During this epoch, dinosaurs flourished as huge herds of sauropods, such as Brachiosaurus and Diplodocus , filled

5320-492: Was assembling. The breakup of Pannotia began with the opening of the Iapetus Ocean and other Cambrian seas and coincided with a dramatic rise in sea level. Paleoclimatic studies and evidence of glaciers indicate that Central Africa was most likely in the polar regions during the early Paleozoic. The breakup of Pannotia was followed by the assembly of the huge continent Gondwana ( 510  million years ago ). By

5396-928: Was comparatively mild. The sole major Mesozoic orogeny occurred in what is now the Arctic , creating the Innuitian orogeny , the Brooks Range , the Verkhoyansk and Cherskiy Ranges in Siberia, and the Khingan Mountains in Manchuria. This orogeny was related to the opening of the Arctic Ocean and suturing of the North China and Siberian cratons to Asia. In contrast, the era featured

5472-537: Was distant from its shores, temperatures fluctuated greatly, and the interior probably included expansive deserts . Abundant red beds and evaporites such as halite support these conclusions, but some evidence suggests the generally dry climate of the Triassic was punctuated by episodes of increased rainfall. The most important humid episodes were the Carnian Pluvial Event and one in the Rhaetian ,

5548-538: Was dominated by deserts in the interior of the Pangaea supercontinent. The Earth had just witnessed a massive die-off in which 95% of all life became extinct, and the most common vertebrate life on land were Lystrosaurus , labyrinthodonts , and Euparkeria along with many other creatures that managed to survive the Permian extinction. Temnospondyls reached peak diversity during the early Triassic. The Middle Triassic, from 247 to 237 million years ago, featured

5624-683: Was reflected in greater diversity and complexity of the trace fossils they left behind. After two decades of deliberation, the ICS chose Fortune Head , Burin Peninsula, Newfoundland as the basal Cambrian Global Stratotype Section and Point (GSSP) at the base of the Treptichnus pedum assemblage of trace fossils and immediately above the last occurrence of the Ediacaran problematica fossils Harlaniella podolica and Palaeopsacichnus . The base of

5700-602: Was still dominated by cycads and ferns until after the Cretaceous–Paleogene extinction. Some plant species had distributions that were markedly different from succeeding periods; for example, the Schizeales , a fern order, were skewed to the Northern Hemisphere in the Mesozoic, but are now better represented in the Southern Hemisphere. The extinction of nearly all animal species at the end of

5776-485: Was the height of archosaur diversity, and the first birds and eutherian mammals also appeared. Some have argued that insects diversified in symbiosis with angiosperms, because insect anatomy , especially the mouth parts, seems particularly well-suited for flowering plants. However, all major insect mouth parts preceded angiosperms, and insect diversification actually slowed when they arrived, so their anatomy originally must have been suited for some other purpose. At

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