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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

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


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
  • “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 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 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

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?