Mesozoic life wrap up
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Mesozoic life wrap-up. Plants, dinosaurs, birds, and mammals. Plants are:. Seedless plants (vascular and nonvascular) Many divisions Important in Paleozoic: Ferns, Sphenopsids, Lycophytes Gymnosperms: ‘naked seeds’ Angiosperms: ‘seeds in a vessel’.

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Mesozoic life wrap-up

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Mesozoic life wrap up

Mesozoic life wrap-up

Plants, dinosaurs, birds, and mammals

Plants are

Plants are:

  • Seedless plants (vascular and nonvascular)

    • Many divisions

    • Important in Paleozoic: Ferns, Sphenopsids, Lycophytes

  • Gymnosperms: ‘naked seeds’

  • Angiosperms: ‘seeds in a vessel’

Paleozoic: Lycopods grew to giant forests!

Two Sphenophytes

Geologic sequence

Geologic sequence

  • Nonvascular plants (eg Cooksonia + friends)

  • Vascular seedless

    • Example: Lycophytes, Sphenopsids

      • Giant Lycopod trees in Paleozoic; now small

      • Horsetails are modern remnant of major Paleo. Sphenops

  • Evolution of seeds! Spermatophytes

    • Gymnosperms: late Paleozoic

    • Angiosperms: mid-Cretaceous (late Mesozoic)

Angiosperms are special because

Angiosperms are special because:

  • Insect-polinated instead of wind polinated

    • Insect relationship allows for new means of plant diversification: evolve to match a specific bug

  • Animal-dispersed via fruits

    • Encase seeds bribing animals to disperse

  • Animal and insect relationships allow more rapid dispersion + more remote existence

  • Seed comes with its own early nutrition inside

The diversification of reptiles

The Diversification of Reptiles

  • Reptile diversification began

    • during the Mississippian Period

    • with the evolution of the first animals to lay amniotic eggs

  • From this basic stock of so-called stem reptiles

    • all other reptiles, as well as birds and mammals, evolved

Reptiles and birds

Reptiles and Birds

  • Relationships among fossil and living reptiles and birds

First dinosaurs

First Dinosaurs

  • Evolved from archosaurs (reptiles)

  • Late Triassic

  • Small, only 3 ft long

  • Major characteristics

    • Can walk fully upright - bipedal

    • Special hip and ankle structure

Archosaurs and the origin of dinosaurs

Archosaurs and the Origin of Dinosaurs

  • Reptiles known as archosaurs

    • archo meaning "ruling" and sauros meaning "lizard”

  • include crocodiles, pterosaurs (flying reptiles), dinosaurs, and the ancestors of birds

  • Including such diverse animals

    • in a single group implies

    • that they share a common ancestor

    • and indeed they possess several characteristics that unite them

  • Dinosaurs orders

    Dinosaurs Orders

    • All dinosaurs possess

      • a number of shared characteristics,

      • yet differ enough for us to recognize two distinct orders

        • the Saurischia

        • and Ornithischia

    • A distinctive pelvic structure characterizes each order

      • 3 bones in pelvis: illium, ischium, and pubis

      • Saurischian: pubis points down

      • Orinischian: pubis points back

    Distinctive pelvic structure

    Distinctive Pelvic Structure

    • Saurischian dinosaurs

      • have a lizardlike pelvis

      • and are thus called lizard-hipped dinosaurs

    • Ornithischians

      • have a birdlike pelvis

      • and are called bird-hipped dinosaurs

    • Convergent evolution

      • ‘birdlike’ pelvic structure reinvented in Saurischian descendents (avian dinosaurs = birds)

    Hip structure

    Hip Structure

    MSN encarta

    Saurischian dinosaurs

    Saurischian Dinosaurs

    • The saurischians,

      • include two distinct groups

      • known as theropods and sauropods

    • All theropods

      • were carnivorous bipeds

      • ranging in size from tiny Compsognathus

      • to giants such as Tyrannosaurus

        • and similar species

        • that might have weighed

        • as much as 7 or 8 metric tons

    Dinosaur cladogram

    Dinosaur Cladogram

    • Cladogram showing dinosaur relationships

      • showing Pelvises of ornithischians and saurischians

      • Among the several subgroups of dinosaurs

    • theropods were carnivores

    • all others were herbivores





    Dinosaur cladogram1

    Dinosaur Cladogram

    Small theropod dinosaur

    Small Theropod Dinosaur

    • Compsognathus weighed only 2 or 3 kg

      • Bones found within its ribcage indicate it ate lizards



    • The skull of Tyrannosaurus,

      • another theropod,

      • measured more than 1 m long



    • Included among the sauropods

      • are the truly giant, quadrupedal herbivorous dinosaurs

      • Apatosaurus, Diplodocus, and Brachiosaurus, the largest known land-animals of any kind

    • Brachiosaurus,

      • a giant even by sauropod standards,

    • weighed as much as 75 metric tons,

    • partial remains indicate that even larger sauropods may have existed

    Dinosaur cladogram2

    Dinosaur Cladogram



    • “Bird-hipped” dinos

    • Herbivorous dinos (eg. stegosaurus)

    • Did not lead to birds! (Birds evolved from carnivorous dinos with saurischian hip)

    Warm blooded dinosaurs

    Warm-Blooded Dinosaurs?

    • Were dinosaurs endotherms

      • warm-blooded : generates internal heat to maintain body temperature

    • like today's mammals and birds,

  • or were they ectotherms

    • cold-blooded: relies on the environment + behavior to regulate body temperature

  • as are all of today's reptiles?

  • At some point between dinosaur and bird, became endothermic. When?

  • Evidence for endothermy large brain

    Evidence for Endothermy: Large Brain

    • Brain size correlates with endothermy in modern mammals and reptiles

      • Some dinosaurs had more brain per body than modern reptiles

      • Problems: how to measure brain size?

        Value of correlative data?

    Evidence for endothermy insulation

    Evidence for Endothermy: Insulation

    • More compelling evidence for theropod endothermy

      • comes from their probable relationship to birds

      • recent discoveries in China of dinosaurs with feathers or a feather-like covering

    • Today, only endotherms have hair, fur, or feathers for insulation

    Evidence for endothermy

    Evidence for Endothermy:

    • Dinosaurs present at high latitudes

      • Problem: Cretaceous Interior Seaway

    • Predator/prey relationship

      • Endotherms eat more therefore an ecosystem can support fewer of them

      • Fossil record suggests many herbivores, fewer carnivores

    Evidence for endothermy dominance over mammals

    Evidence for Endothermy: dominance over mammals

    • Endotherms can move fast for long periods of time

    • Ectotherms can only do short bursts

    • Other possible explanations for dinosaurian head start over mammals?

    Triassic extinction

    Triassic Extinction

    Triassic extinction1

    Triassic Extinction

    • Hit mammals hard

    • Dinosaurs not as affected

    • Possible cause:

      • Pangaea fragmentation lead to volcanic CO2 release

      • CO2 greenhouse?

      • Evidence: plant fossils show fewer stomates: pores to admit CO2

    Mammal ancestry paleozoic

    Mammal ancestry, Paleozoic

    • Therapsids --> Cynodonts

      • mammals

    • Thecodontians

      • Stem reptiles

        • Plesiosaurs

        • Icthyosaurs

        • Archosaurs

        • Other reptiles



    • Mammals have hair, make milk, have 3 ear bones, and are warm-blooded

    • Marsupials and placentals give birth to live babies

    • Monotremes lay leathery eggs

    • Some have very short pregnancies and carry immature babies in pouches (all marsupials and some monotremes)

    Tree of life Web Project



    • Evolved from cynodonts in Late Triassic

      • Strong fossil record of transition:

      • Bone structure (jaw and ear)

      • Many types of teeth

      • Only 2 sets of teeth

      • Teeth meet for grinding

      • Skin instead of scales

  • Remained mouse-sized for 150 m.y.

  • First mammals

    First Mammals

    Birds evolved in the jurassic

    Birds evolved in the Jurassic

    • Archaeopteryx

    • Feathers and wings

    • No bill

    • Reptilian backbone

    Archaeopteryx s feathers

    Archaeopteryx’s Feathers

    • Not clear if Archaeopteryx could fly or only glide

    • Did feathers evolve:

      • For flight

      • For insulation

      • For display

    • Maybe another example of evolutionary opportunism

      • Feathered, non-flying theropods found in China

    K t boundary extinction review

    K/T Boundary Extinction Review

    • Greatest mass extinction took place at the end of the Paleozoic Era

    • K/T extinction has attracted more attention because it affected dinosaurs

    K t boundary extinction

    K/T Boundary Extinction

    • N America suffered most

    • Also going on: seas cooling, receding globally

    • Many animals in decline before K/T boundary

    • Mammals, birds, turtles, crocodiles, lizards, snakes and amphibians survived

    K t boundary

    K/T Boundary

    What did earth look like 65 ma

    What did Earth look like 65 Ma?

    What caused the k t extinction

    What caused the K/T extinction?

    • One proposal has become popular since 1980

      • based on a discovery in Italy

      • 2.5-cm-thick clay layer at the Cretaceous-Tertiary boundary with a remarkably high concentration of iridium

    • Worldwide iridium layer now known

    Cretaceous tertiary boundary

    Cretaceous-Tertiary Boundary

    • K/T boundary site in Italy

    • 2.5-cm-thick clay layer shows high concentration of iridium

    Boundary clay

    Boundary Clay

    • Closeup view of the boundary clay in the Raton Basin, New Mexico

    Mesozoic life wrap up

    Boundary Clay

    • Deep sea core

    • Recovered by Joides Resolution in 1997

    Iridium anomaly

    Iridium Anomaly

    • Significance of the iridium anomaly

      • iridium is rare in crustal rocks

      • found in much higher concentrations in some meteorites

      • May also result from expoure to supernovas (but supernovas also create isotopic anomalies not present at K/T)

    • Accordingly, some investigators propose

      • meteorite impact explains the anomaly

      • meteorite perhaps 10 km in diameter

      • impact set in motion a chain of events leading to extinctions

    Boundary sites

    Boundary Sites

    • North American Cretaceous-Tertiary boundary sites also contain

      • soot

      • shock-metamorphosed quartz grains

    Meteorite impact crater

    Meteorite Impact Crater

    • Centered on Chicxulub on the Yucatán Peninsula of Mexico

    • Discovered in 1950’s, interpreted to be volcanic

    Chicxulub crater

    Chicxulub Crater – GAIL CHRISTESON

    Chicxulub crater1

    Chicxulub Crater

    Chicxulub crater2

    Chicxulub Crater

    Chicxulub crater3

    Chicxulub Crater

    Impact site

    Impact Site

    • Centered on the town of Chicxulub, Yucatan Peninsula of Mexico

    • The 180-km diameter structure lies beneath layers of sedimentary rock and appears to be the right age

    Evidence at chicxulub

    Evidence at Chicxulub

    • Shocked quartz

    • tektites, small pieces of rock that were melted during the proposed impact and hurled into the atmosphere

    • Nearby in the Carribean: tsunami deposits

    What happened

    What happened?

    The moment of impact 65 million years ago near what is now the Yucatan Peninsula ...

    ... and the Chicxulub crater, a few days later. Note the inner ring.

    Impact consequences

    Impact Consequences

    • According to the impact hypothesis

      • 60 times the mass of the meteorite was blasted from the crust high into the atmosphere

      • heat generated at impact started raging forest fires that added more particulate matter to the atmosphere

    • Sunlight was blocked for several months

      • caused a temporary cessation of photosynthesis

      • food chains collapsed and extinctions followed

    Acid rain

    Acid Rain

    • With sunlight greatly diminished, Earth's surface temperatures were drastically reduced, adding to the biologic stress

    • Another proposed consequence of an impact is that sulfuric acid (H2SO4) and nitric acid (HNO3) resulted from vaporized rock and atmospheric gases

    • Both would have contributed to strongly acid rain that might have had devastating effects on vegetation and marine organisms



    • Correlation between extinction and meteorite impact is pretty clear

    • But correlations don’t prove causality!

    • Remaining questions:

      • Did terrestrial and marine extinctions occur simultaneously?

      • If small animals survived, why didn’t small dinosaurs survive?

      • Was there a relationship between the extinctions and ongoing volcanic activity?

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