Breakup of Pangea

1
Breakup of Pangea

• Pangea breaks up in four stages
• Triassic - North America and Gondwanaland rift
  apart Atlantic starts to form
• Africa and Antarctica/Australia rift apart
• End of Jurassic - Eurasia rotates, closing off
  Tethys, while South America and Africa rift
  (separated completely by 70 Ma)
• North America and Eurasia completely separate in
  Atlantic (Cenozoic)

2
West Coast of North America

• As the Atlantic grew, the Pacific began to shrink
• The Mesozoic saw lots of material added to the
  west coast of North America - island arcs,
  continental fragments - each of which extended
  the continent a bit and tended to form mountain
  ranges

3
West Coast of North America

• More than 50 distinct chunks (displaced
  terranes) have been described in the Cordilleran
  region - comprise 70 of the area
• Some were so large that they just stuck on
  others were just the lower-density material
  riding on the oceanic crust that got scraped off

4
West Coast of North America

• New crust is not only these Pacific bits, but
  also Andes-style subduction mountains, volcanism,
  and sedimentary erosion

5
West Coast of North America

• Several main orogenic events
• Sonoma orogeny around the start of the Mesozoic -
  volcanic arc crashes into coast
• Nevadan orogeny in Triassic (and later in
  Jurassic) - sediments weathering off mountains
  get folded and crushed into new mountains

6
West Coast of North America

• Sevier orogeny - Middle Jurassic to Cenozoic -
  east of modern Sierra Nevada mountains - lots of
  low-angle thrust faults and folding - possibly
  100 km of shortening along the coast
• Laramide orogeny (Rocky Mountains) - high angle
  reverse faults (become thrust faults with depth)
  and folds deform the inner part of the continent
  past the coastal margin

7
Dinosaurs

• Major classifications hinge on the number of
  holes in the temple area of the skull (behind the
  eyes)
• Diapsida - two openings - includes dinosaurs,
  flying reptiles, and all living reptiles except
  turtles
• Synapsida/Euryapsida - one opening - synapsids
  low opening, euryapsids high opening
• Anapsida - no openings

8
Dinosaurs

• Term coined by Sir Richard Owen in 1842 - means
  terrible lizard
• He only knew of three types Megalosaurus,
  Iguanodon, and Hylaeosaurus
• Since then there have been hundreds of species
  discovered and described, so dinosaur is a very
  broad term

9
Whats not a dinosaur?

• Dimetrodon
• Dimetrodon is a synapsid - not a reptile or a
  mammal but earlier than both

10
Whats not a dinosaur?

• Pterosaurs
• These guys are definitely reptiles, but not as
  closely related to dinosaurs
• Not ancestral to birds or bats - this is a case
  of convergent evolution

11
Whats not a dinosaur?

• Pterosaurs
• These guys are definitely reptiles and diapsids,
  but are not true dinosaurs
• Not ancestral to birds or bats - this is a case
  of convergent evolution

12
Pterosaurs

• As pterosaurs get developed, they evolve into
  more flight-adapted structures

13
Pterosaurs

• Big eyes, large brain, probably endothermic (wing
  structures show thermoregulation)

14
Pterosaurs

• How did they get to fly? How did birds get to
  fly?
• Two ideas -
• Ground up hypothesis - organisms started on the
  ground, began gliding behavior
• Arboreal hypothesis - organisms started in trees,
  developed gliding to accommodate transport (e.g.
  flying squirrel)
• Pterosaurs look like ground-up types from fossil
  record

15
Triassic reptiles

• Many new reptile groups show up in the Triassic,
  including turtles and early dinosaurs
• One main group was the archosaurs - includes
  crocodiles, pterosaurs, dinosaurs, and thecodonts
  (dinosaur ancestors)

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Thecodonts

• Small, agile, slight reptiles
• Many were bipedal - what are the advantages of
  bipedalism?
• Some revert to four-legged walking - again
  convergent evolution toward crocodiles

17
Dinosaurs

• Two groups-
• Saurischia (lizard-hipped)
• Ornithischia (bird-hipped)
• First ones are about 225 Ma - Triassic
• Some saurischians are Theropods - big,
  carnivorous dinosaurs including Allosaurus and
  Tyrannosaurus.

18
Dinosaurs

• Another saurischian group is the Sauropods, large
  herbivores.
• Earliest were bipedal, but later they got huge -
  e.g. Brontosaurus (now called Apatosaurus),
  Supersaurus, Ultrasaurus (over 80 tons, 35 meters
  long). Diplodocus and Seismosaurus
• Can they live on land or in water?
• Sauropods first arrive in early Jurassic