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THE EARLY MESOZOIC. Middle Life Intermediate Evolutionary Forms “The Age of Reptiles” Dinosaurs ruled the Earth Evolution of Birds, Mammals and Flowering Plants 182 million years. The Early Mesozoic. Triassic- Tri or Three Friedrich August von Alberti

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The early mesozoic l.jpg

  • Middle Life

  • Intermediate Evolutionary Forms

  • “The Age of Reptiles”

  • Dinosaurs ruled the Earth

  • Evolution of Birds, Mammals and Flowering Plants

  • 182 million years

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The Early Mesozoic

  • Triassic- Tri or Three

    • Friedrich August von Alberti

    • Unit between Zechstein and Lias Limestones of Germany

    • Red non-marine sandstones-Marine Muschelkalk-Red non-marine marls and clay

  • Jurassic

    • Highly fossiliferous, ammonites

    • Alexandre von Humboldt> Jura-kalk-stein, 1799

    • Jura Mountains: France & Switzerland

  • 85 my

Paleogeography l.jpg

  • Continental fragmentation> Rifting

  • Break-up occurred in Late Triassic

  • Northern hemisphere rifted from southern and then east rifted from west producing many blocks

  • In the Jurassic, Gulf of Mexico continued to open

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  • East Coast of the US

  • Rifting >Atlantic Ocean

  • Fault-block basins along

  • the east coast from Nova

  • Scotia to S. Carolina

  • Triassic Redbeds and Basalts

  • The Newark Supergroup

    • Fluvial & Lacustrine Red

    • beds

    • Sills and Dikes

    • Vertebrate Footprints

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GULF of MEXICO- Evaporite sequences of the Jurassic deposited

in the initial rift sequence

The salt domes can be as high as 20km and have 2km diameters

Salt rises due to low density

These diapirs are good oil traps in Texas and Louisiana

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Tectonic History deposited

  • Cordilleran Orogenic Belt

    • Western North America-South America

    • 300-1000km wide

    • Terrane accretion

      • Wrangelia Traveled 5000KM

    • Jurassic to today

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Middle Triassic Sonoman Orogeny deposited

Early Jurassic Nevadan Orogeny

Suturing of Exotic terranes to western US

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Orogenic events created igneous deposited

plutonic intrusions, batholiths,

like the Sierra Nevada Batholith

and the Idaho Batholith

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Sierra Nevada Batholith deposited


Neoproterozoic to cenozoic transgressions and regressions observed on the craton l.jpg

Variable sea level represented sequences of sediments bounded by unconformities on all of the cratons -

Regression, very low sea level

during the Triassic

Zuni Transgression in Jurassic

through Cretaceous, very high

sea level

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Early Jurassic of the Western US OBSERVED ON THE CRATON

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Chinle Fm. Petrified Forest OBSERVED ON THE CRATON

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Petrified National Forest OBSERVED ON THE CRATON

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Regular Echinoid OBSERVED ON THE CRATONCidaris

Irregular Echinoid Hemiaster

Rapid Radiation of Mesozoic Sea Urchins

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Ceratitic Ammonoid from the OBSERVED ON THE CRATON


Radiation of the Ammonoids

Best Index Fossils for the Jurassic

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Diversification of Reptiles OBSERVED ON THE CRATON

Marine Reptiles


Flying Reptiles


The Dinosaurs

Pelvic Bone Arrangement





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The Dinosaurs: Middle Triassic OBSERVED ON THE CRATON

Differences Based on Pelvic Bone Arrangement: Late Triassic Evolution

  • Saurischian

    • Lizard Hipped, earliest group

    • Similar to thecodonts

    • Theropods (carnivorous dinosaurs); Prosauropods (herbivores); Sauropods (large herbivores)

  • Ornithischian

    • Bird Hipped, differentiated

    • Herbivorous dinosaurs evolved from Prosauropods

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Carnivorous vs. Herbivorous OBSERVED ON THE CRATON

  • Carnivores

    • large head compared to body

    • Tyrannosaurus velocity 60km/hr

  • Herbivores

    • small head compared to body

    • Apatosaurus velocity 10-12km/hr

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Plateosaurus OBSERVED ON THE CRATON: Late Triassic

Sauropod ancestor

Herrerasaurus: one of the oldest

Dinosaurs from the Triassic

Coelophysis: Theropod, carnivorous


The Sauropods: Largest of the


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  • Approximately 700 species in 300 genera

  • Warm Blooded

    • Rapid metabolism; prey-predator ratio; many blood vessels pores in the bones

  • Reproduction and Habits

    • Nesting behavior and social behavior (herds)

  • Characteristics

    • Eoraptor earliest thecodont; sauropods long necks and large body quadrupeds; Ornithopods are bi-pedal herbivores (Camptosaurus); Stegosaurs and Ceratopians are quadruped herbivores

  • Extinction>Late Jurassic-Early Cretaceous/End K

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  • Mammal-like reptiles therapsids (cynodonts)

  • Early Triassic small cynodont gave raise to medium size carnivores and herbivores that are ancestral to mammals

  • Late Triassic a small cynodont gave rise to the earliest mammal the morganucodontids

  • Most Triassic and Jurassic mammals were insectivores and very small

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Archaeopteryx OBSERVED ON THE CRATON: Jurassic Bird or Feathered Dinosaur

from the Solnhofen Fm. Of Germany

Birds arose from coelosaurs in the Jurassic.

Early birds differed from dinosaurs in feathers and a wishbone

Teeth were lost in all birds before the end of the Cretaceous and the tail

was shortened

The pelvic structure was first similar to other theropods (saurischians)

but later through parallel evolution shifted to an ornithischian form

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  • Warming trend which reached a maximum in the Late Jurassic and Cretaceous

  • Variable and cooler temperatures since Late Cretaceous

  • Abundant redbeds, evaporites and carbonates

  • Warmer mid latitude and high latitude rainfall as evidenced by coal deposits for a mild polar condition

  • Oxygen levels were low during Triassic (15%) and rose to 25% then lowering to 21% by the Late Jurassic

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Terrain Cretace, France

Creta: Chalk (Latin)

J.J. d’Omalius d’Halloy (1822)/ Conybeare & Phillips (1822)

144 my to 66.4 my

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Chalk: White Cliff along the Dorset Coast of Southern England

Close-up of chalk with flint (chert) nodules

Higher CO2 from rifting higher productivity of phytoplankton

(coccolithosphorids), chalk deposits and higher O2

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Cretaceous England

  • 70 my

  • Sea level higher>> epeiric seas

  • Divergence of planktic organisms

  • Large coal and oil deposits

  • Atlantic continued to open

  • Tethys closed

  • India migrated northward

  • 3rd largest mass extinction K/T

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Paleogeography England

  • Tectonic events

    • Rifting between Africa-S. America;

      • India-Antarctica/Australia;

      • Britain-New Foundland;

      • Madagascar-Africa

    • Collisions Sevier and Laramide orogeny in western US

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Cordilleran Orogenic System England

  • Terrane accretion

  • Subduction

  • Intense deformation

  • Fold-thrust belts

  • Plutonism & Volcanism

  • Sevier Orogeny

    • 130-80 my

  • Laramide Orogeny

    • 80-50 my

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Cross-section indicating major tectonic features present England

in the Cretaceous across the western US

Fold/Thrust Belt


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Highest stand of sea-level England

280m above current

Atlantic coastal plain


Florida was a shallow

submarine carbonate bank

Black shales: carbonaceous

matter from unoxidized

phytoplankton due to lack

of polar cold water


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Diagrams indicating how rapid sea-floor spreading can England

cause displacement of water onto continents

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Fall Line England

Area of outcrop of Cretaceous limestone and marl in the Atlantic

and Gulf Coast Coastal Plain

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Cretaceous Climates England

  • Warm tropical climates

  • Shallow seas, carbonates

  • Coal, bauxite evidence of humid conditions

  • Tropical and subtropical climates extended from 45oN to 70oS

  • Polar regions mild

  • Widespread reefs (Rudists and Corals)

  • Oxygen levels 30% to 35%

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Warm Climates England

  • Decrease reflection of sunlight by high stands of sea levels

    • water absorbs more heat

  • Paleogeographic changes-

    • changes in currents due to plate tectonics, circumequatorial current

  • Increase CO2 in the atmosphere released by mantle plumes, greenhouse effect

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Economic Deposits England

  • Oil, Gas and Coal

  • Oil

    • Phytoplankton-biologic material-source beds

    • Heat-converts to hydrocarbons

    • Permeable beds- reservoir

    • Geologic traps-impermeable beds

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Cretaceous Life England

  • Marine Communities

    • Pelagic diversification of planktic coccoliths, forams, diatoms and dinoflagellates;

    • Nektics ray-fin fishes (Teleost), ammonoids, plesiosaurs, ichthyosaurs, mosasaurs

    • Benthic forams, major expansion of filter and deposit feeders

  • Terrestrial Communities

    • Appearance of angiosperms

    • Coevolution of pollinating insects

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Extinctions England

  • K/T Boundary

  • Dinosaurs, pterosaurs, many marsupial mammals became extinct

  • Extinction for terrestrial organisms only 15%

  • Marine extinctions at the generic level 70%

  • All ammonites, rudists, marine reptiles

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Causes of Extinction at the K/T Boundary England

  • Sea Level changes

  • Temperature changes

  • Increased seasonality

  • Changes in plant distribution and extinction

  • Increased competition with mammals

  • Bolide collision

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Impact Theory England

  • Iridium Anomaly

    • clay around K/T enriched in Ir

  • Spherules

    • glass beads, felsic, melting of crustal rocks

  • Soot

    • carbonaceous particles, wildfires

  • Shocked Quartz

    • lamelle > high pressure shock wave

  • Stishovite

    • high pressure form of quartz

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Occurences of Iridium-rich sediments at the K/T England

Shocked Quartz

Iridium-rich clay layer

Gubbio, Italy



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Location of Chicxulub structure England

Meteor Crater, AZ

30m bolide

Excavated 1.2km crater

Phobos, a Martian moon about 20km diameter

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Volcanic Model England

  • Iridium as aerosol from volcanism

  • Large eruption of flood basalts

    • Deccan Plateau

    • Periodicity of 30 my of basalts coincide with extinction peaks

  • Sulfates >> acid rain > pH

  • Cooling due to erupted ash

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Erupted at 66 my England

3 periods each lasting

50,000-100,000 yrs

Millions of cubic kilometers

of magma