Introduction 1 Early Paleozoic a Cambrian Ordovician b Conspicuous fossils c Most animal phyla appeared 2 Cambrian a Global transgression b Rapid diversification of life in the ocean i Early Cambrian Explosion 3 Ordovician a b Ordovician radiation c Glaciation related global mass extinctions first ever Period of sustained higher sea level Early Cambrian 1 Neoproterozoic biota was primarily soft bodied 2 Base of early Cambrian a Index fossil treptichnus pedum i Complex burrower branching ii The first occurrence is roughly coincident with the last appearance of Ediacaran fauna 3 Many early Cambrian groups evolved skeletons a Divided accordingly into three intervals i Lowermost Cambrian 1 Simple tube shaped or vase shaped skeletons 2 Some with small teeth ii Tommatian fauna lower Cambrian 1 Small skeletal elements 2 Gastropod mollusk sponge spicule 3 Some not assigned to a living phylum 4 Occupied seas 3 4 Ma a Sudden disappearance iii Large animals with skeletons 1 Trilobites a Calcified segmented exoskeleton arthropods b Deposit feeder c Diversified quickly d Shared seafloor with brachiopods echinoderms and mollusks 2 Anomalocarids carnivorous invertebrates Cambrian Explosion 1 Cambrian life in the sea a Cambrian explosion i Rich in visible fossils ii Radiation of new life forms with skeletons 2 Terrestrial realm a Barren b No insects no vertebrates c Only simplest living things on land 3 Marine Biota a Benthic i Deposit feeders ii Grazers 1 Trilobites arthropods echinoderms 1 Monoplacophoran mollusks iii Suspension feeders 1 Brachiopods 2 Sessile echinoderms a Eocrinoids b Short stalks b Pelagic i Zooplankton 1 2 Planktonic Trilobites Jellyfishes carnivores ii Phytoplankton 1 Acritarchs iii Stromatolites and Trombolites 1 Progressively less abundant with animal appearance c Oldest organic reefs Archaeocyathids i Sponge suspension feeders ii Encrusted by algal and bacterial mats 4 Middle and Late Cambrian spanning 15 Ma a 140 trilobite families b Vertebrate animals diversified c Conodonts small swimming predatory animals i Teeth abundant and diverse d Isolated bony external plates found indicate existence of fish likely deposit feeders 5 Middle Cambrian Burgess Shale fauna a Well preserved soft bodied animals i Soft body arthropods related to trilobites ii Polyaete worms iii Onychophorans 1 Worm like creature with walking legs iv Opabina with five eyes and a food gathering pincer v Marine chordates 1 Pikaia which possessed a notochord the primitive structure that evolved into a backbone Cambrian Extinctions 1 Three mass extinctions of trilobites a Trilobite species mass extinctions in tropical seas b Followed by new evolutionary radiation or re diversification c Third major extinction defines Cambrian Ordovician boundary Ordovician Life 2 Early Ordocivian animals were swimmers and floaters a Trilobites remained abundant b Nautiloids cephalopods c Graptolites floating zooplankton 3 Middle Late Ordovician most dramatic evolutionary expansion of marine realm a Threefold increase in number of animal families 4 Life in the sediment burrowing animals a Expansion of burrowers i Bivalves ii Worms iii Trilobites b Increasing bioturbation 5 Life on the seafloor benthic organisms a Increased diversity of benthic organisms i Trilobites ii Grazing snails iii Articulate brachiopods iv Crinoids v Starfish vi Major reef building coral communities 1 Tabulate head corals 2 Stomatoporoids sponges 3 Rugose horn corals 6 Life above the seafloor advances in predation a Nautiloids Jet propulsion i Well developed eyes ii iii Tentacles to capture prey b Starfish on the seafloor also predators c Resulted in the decline of stromatolites 7 Extinction sets back marine diversification a 1300 genera of marine invertebrates recognized in Upper Ordovician rocks i Number declines sharply at the end of Ordovician b Similar extinctions occur repeatedly during Paleozoic c Less in Mesozoic and Cenozoic Cambrian Paleogeography 1 Clustered cratons of the Neoproterozoic rifted during Cambrian a Laurentia Siberia Baltic rift from Gondwanaland b Laurentia positioned near equator i Progressively flooded during Cambrian 2 Shallow water limestone accumulation a Perhaps one of the largest transgressions of the Phanerozoic 3 Gondwanaland above sea level due to orogenic uplift 800 500 Ma 4 Transgression a Sediment eroded from land and deposited along continental margins b Continued rise resulted in limestone deposits over the siliciclastic sediments Ordovician Paleogeography 1 Baltica migrated northward into the tropics a Tropical limestone accumulation present day Baltic Sea b Bahama bank like oolite deposits 2 Gondwanaland located at south pole a Large glacier growth in Late Ordovician 3 Avalonia breaks from Gondwanaland moving northward toward Laurentia Island arc forms as ocean is consumed between Laurentia and Avalonia 4 fragments 5 Progressive convergence exotic terrane sutures along eastern Laurentia Regional Paleozoic 1 Eastern Laurentia a Taconic orogeny collective mountain building events of Ordovician i First event in formation of Appalachian mountain belt ii Collision of several islands and Avalonia 1 Evidenced by sedimentary record a Classic foreland basin sequence b Ash fall indicating proximity of volcanic arc b Classic foreland basic succession i Downwarping into subduction zone bordering an island arc c Changes in basin black shales i Wide shallow carbonate platform replaced with deep water ii Black shales replaced by flysch deep water turbiditites iii Flysch replaced by molasses non marine clastics d Foreland basin developed during the Taconic orogeny e Clastic wedges of coarse sediment shed inland from newly formed f Ash beds now clay evidence of volcanic arc between Laurentia and mountains east Baltica 2 Western Laurentia a Passive margin b Northward in British Columbia Burgess Shale formed at base of steep carbonate shelf i Absence of oxygen ii Fauna likely shallow water habitat but swept downslope and buried turbidites Earth System Shift 1 Late Ordovician glaciation mass extinction a Major ice sheets expanded on Gondwanaland at the south pole i Glacial evidence indicates polar location ii Shifts in carbon isotopes indicate burial of isotopically light carbon 1 Brachiopod shells heavier carbon isotopes iii Less carbon decomposition less CO2 back to atmosphere global cooling b Extinction of 50 of marine genera i Seafloor brachiopods trilobites bryozoans corals ii Benthic acritarchs graptolites conodonts