Mesozoic Earth and Life History

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Charles Walcotts Burgess Shale
-middle Cambrian shale in the Rockies of western
Canada
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Trilobites
Brachiopods
Crinoids
Sponges
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Anomalocaris
Hallucigenia
Pikaia
Sidneyia
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Leanchoilia--China
Leanchoilia--Burgess
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Mesozoic Earth and Life History
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Introduction

• The Mesozoic began 245 mya and ended 66 mya
• Three periods - Triassic, Jurassic, Cretaceous
• breakup of Pangaea was the major geologic event
• tectonism and sedimentation are used to classify
  the Mesozoic in N. America

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The Breakup of Pangaea

• The movement of continents during and after the
  breakup affected global climate and oceanic
  regimes as well as that of individual continents
• ocean basins were created, and new mountain
  ranges built

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Global Climates and Ocean Circulation Patterns

• Global temperature gradient increased as
  separating continents interfered with oceanic
  circulation patterns and displaced water at
  higher latitudes
• Oceanic and atmospheric circulation patterns also
  accelerated

• Mesozoic climates were more equable, lacked the
  strong north-south climate zones of today, and
  offered plants and animals more opportunities to
  occupy more extensive geographic ranges

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Mesozoic History of North America

• Tectonic and sedimentary events
• Gulf of Mexico began to form and experienced
  evaporite deposition
• major mountain building began in the Jurassic for
  the entire Cordillera
• global rise in sea level in the Cretaceous

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Eastern Coastal Region

• Early Triassic saw coarse detrital sediments
  deposited from the erosion of Appalachian
  highlands
• eroded to a flat plain by the Cretaceous
• fault-block basins developed as N. America
  separated from Africa and filled with coarse,
  red, nonmarine sediment
• dikes and sills

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Gulf Coastal Region

• Thick evaporites formed in the Gulf
• normal marine deposition returned to the Gulf by
  Late Jurassic, with transgressions and
  regressions
• thousand of meters of sediments were deposited

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Western Region

• Complex history, involving the subduction of the
  Pacific plate under the N. American
• island arcs created were thrust against the
  craton - Sonoman orogeny

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Western Region
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Western Region

• Cordilleran orogeny
• Nevadan - Jurassic batholith intrusion in the
  Sierra Nevada and elsewhere on the western edge
• Sevier - thrust faulting to the east
• Laramide - built the present day Rockies

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Mesozoic sedimentation

• Triassic
• shallow-water marine clastics
• red beds
• Jurassic
• clean cross-bedded sandstones
• marine sediments in the Sundance Sea
• Cretaceous
• extensive marine deposition, thin to the east

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Life of the Mesozoic Era

• Age of Reptiles
• most diverse and abundant land dwellers
• Mammals appear
• Birds evolve
• Flowering plants evolve
• Marine invertebrates recover

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Flourishing of Marine Invertebrates
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Plants - Primary Producers on Land

• Triassic and Jurassic land plants consisted of
  seedless vascular plants and gymnosperms
• Angiosperms (flowering plants) appear in Early
  Cretaceous, similar to magnolias
• the evolution of flowers and an enclosed seed
  ensured their success

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Archosaurs and the Origin of Dinosaurs

• Archosaurs gave rise to crocodiles, pterosaurs,
  dinosaurs, and birds
• Dinosaurs
• Saurischia
• Ornithischia

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Dinosaurs

• Saurischians
• theropods were bipedal carnivores
• sauropods were the giant, quadrupedal herbivores
• Ornithischians
• ornithopods
• pachycephalosaurs
• ankylosaurs
• stegosaurs
• ceratopsians

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From Reptiles to Birds

• The pterosaurs were the first vertebrates to fly
• common from Late Triassic to Cretaceous
• wing membrane supported by an elongated fourth
  finger
• light hollow bones
• development of brain areas associated with
  coordination and sight
• likely to have been endothermic

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Marine Reptiles

• Ichthyosaurs
• Plesiosaurs
• Mosasaurs

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Origin and Early History of Mammals

• Therapsids gave rise to cynodonts, which evolved
  into the mammal class
• skeletal structure is used to identify mammals in
  the fossil record
• differences in the lower jaw and ear in
  particular distinguishes mammals

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Origin and Early History of Mammals

• Mammal diversity remained low throughout the
  Mesozoic
• two branches did develop however
• monotremes
• marsupial and placental

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• Cretaceous-Tertiary extinction claimed dinosaurs,
  flying reptiles, marine reptiles, and many marine
  invertebrates

K-T Mass Extinction - A Crisis in the History of
Life
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