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THE PERMIAN (297-251 MYA).docx

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University of Alberta
Renewable Resources
REN R360
Melanie Muise

 THE PERMIAN (297-251 MYA) o Continents coalesced into the supercontinent Pangaea. o Near the end, reptiles greatly outnumbered the amphibians. o Late in the period, the lineage leading to mammals diverged from one reptilian group. o In fresh waters, the Permian period was a time of extensive diversification of ray-finned fishes. o Massive volcanic eruptions resulted in outpourings of lava that covered large areas of Earth; ashes produced blocked the sunlight and cooled the climate  forming largest glaciers in history. o Atmospheric temperature dropped; about half of the Permian land would have been uninhabitable. o Resulted in the most drastic mass extinction even in Earth’s history. Geographic differentiation increased during the Mesozoic era  Few organisms that survived found themselves in a relatively empty world at the start of the Mesozoic era (251 mya).  Pangaea slowly separated into individual continents; oceans rose and reflooded continent shelves, forming huge, shallow inland seas.  Atmospheric oxygen concentrations gradually rose to their former levels.  Different groups of organisms came to dominate the Earth: o Three groups of phytoplankton---dinoflagellates, cocccolithophores, and diatoms— became ecologically important at this time.  Earth’s biota became increasingly provincialized –distinct terrestrial biotas evolved on each continent.  Biotas of the shallow waters bordering the continents also diverged from one another.  By the end of the era, the continents were close to their present positions and many organisms looked similar to those living today.  THE TRIASSIC (251-200 mya) o Pangaea began to break apart o Many invertebrate groups became more species-rich; many burrowing animals evolved from groups living on the surfaces of seafloor sediments. o Conifers and pteridosperms became the dominant trees. o First frogs and turtles appeared. o Great radiation of reptiles began. o End of this period was marked by mass extinction of about 65% of the species on Earth.  THE JURASSIC (200-145 mya) o Land was once again divided into two large continents. o First salamanders and lizards appeared, and flying reptiles evolved. o Dinosaur lineages evolved into predators that walked on two legs and large herbivores that walked on four. o Several groups of mammals first appeared during this time. o Plant evolution continued with the emergence of the flowering plants that dominate Earth’s vegetation today.  THE CRETACEOUS (145-65 mya) o Laurasia was completely separated from Gondwana. o A continuous sea encircled the tropics. o Sea levels were high, and Earth was warm and humid. o Marine invertebrates increased in diversity and in number. o Dinosaurs continued to diversify and first snakes appeared. o Early in this period, flowering plants began the radiation that lead to their current dominance on land. o By the end, many groups of mammals had evolved; most were small, few were large. The modern biota evolved during the Cenozoic era  By early Cenozoic ear (65 mya), the positions of the continent
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