Mesozoic

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Mesozoic

• Three time periods
• Triassic (245-208 Million Years Ago)
• Jurassic (208-146 Million Years Ago)
• Cretaceous (146-65 Million Years Ago

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Paleo-Meso Timeline

• Land Plants - Ordovician
• Air-breathing arthropods - Silurian
• Amphibians - Devonian, abundant in early
  Carboniferous
• Reptiles - Later Carboniferous

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Paleo-Meso Timeline

• Permo-Triassic - huge extinction
• Sea level fall
• Continents locked up in Pangea in the Southern
  Hemisphere
• Ice caps cover Antarctica, parts of Australia,
  Southern parts of Africa and South America
  (Gondwanaland)

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Paleo-Meso Timeline

• Dinosaurs - Triassic
• Mammals - Triassic
• Birds - Jurassic
• Ammonites become dominant - Jurassic
• Ammonites, Dinosaurs rule all - Cretaceous
• Flowering plants - Cretaceous

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Paleo-Meso Timeline

• Tectonics
• http//www.ucmp.berkeley.edu/geology/

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Big changes in the MesozoicPlants

• Early Mesozoic dominated by ferns, cycads,
  ginkgophytes, and others not widely seen today.
• Modern gymnosperms (e.g. conifers), first
  appeared in their current recognizable forms in
  the early Triassic.
• By the middle of the Cretaceous, the earliest
  angiosperms (flowering plants) had appeared and
  began to diversify - became dominant.

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Mesozoic Developments

• After the Triassic its warmer
• Tethys sea is opening
• Marine plants
• Dinoflagellates flourish (were around in Silurian
  and Permian, but didn't do much)
• Mineralized phytoplankton (Coccolithophorids)
  begin to bloom - great fossil record

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Mesozoic Developments

• Land Plants
• Carboniferous-Permian - big spore-bearing plants
• Mesozoic - pollinating
• Early Mesozoic -Cycads,.Ginkgoes, Seed Ferns,
  Conifers - seeds, but no flowers
• Cretaceous - Flowering plants (angiosperms) with
  enclosed seeds

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Mesozoic Developments

• Land Invertebrates
• Shelled - some rare air-breathing snails,
  freshwater snails and clams
• Arthropods
• Carboniferous-Permian had spiders, millipedes,
  scorpions, centipedes
• Added in Mesozoic are flies, mosquitoes, earwigs,
  wasps, bees, ants and beetles
• Not yet - Butterflies, moths, termites, fleas

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Mesozoic Developments

• Marine Invertebrates
• Big Permian extinction
• Slower rebound - not until middle Triassic
• Pelecypods expanded, eventually outdid
  brachiopods - especially oysters
• Rudists - horn-shaped shells, formed reefs just
  like corals did

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Mesozoic Developments

• Marine Invertebrates
• Corals - same as today, with same requirements
  (zooxanthellae)
• Echinoids
• Ammonoids - good index fossils because of suturing

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End of Mesozoic

• Cretaceous-Tertiary boundary marks a mass
  extinction
• 1/4 of all extant families died out completely
• What evidence is there for a cause?
• Iridium layer
• Shocked quartz
• Glassy spherules - tektites
• Soot from burning

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End of Mesozoic

• Most accepted hypothesis
• Bolide impact - a big object from space smashes
  into the Earth, causing mass destruction
• Chixulub - big crater in the Yucutan peninsula of
  Mexico - appears to be approximately the right age

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End of Mesozoic

• Alternate hypotheses
• Rain of comets -
• Planet X dislodges comets in Oort cloud
• Periodicity of extinctions about 26 million years
• No evidence
• Cosmic rays from a nearby supernova
• Doesnt explain impact-related features
• Why extinctions in ocean, then?

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End of Mesozoic

• Alternate hypotheses -
• Terrestrial explanations
• Sea level drop - less plate activity
• Volcanoes
• How instantaneous was it?
• Not all extinctions happened at end of Cretaceous

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Dinosaurs - Fact and Fiction
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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

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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

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Whats not a dinosaur?

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

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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

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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

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Pterosaurs

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

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Pterosaurs

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

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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

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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

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Dinosaurs

• Supplemental reading (and source of most of these
  cool pictures)
• http//www.ucmp.berkeley.edu/mesozoic/mesozoic.htm
  l

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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.

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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

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Dinosaur Groups - Ornithischians
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Dinosaur Groups - Saurischians
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Dinosaur Groups - Ceratopsians
Triceratops
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Ceratopsians

• Ornithischians
• Emerged at start of Cretaceous
• Some reached 5-6 tons in weight, SUV in size
• Probably traveled in herds - good way to avoid
  extensive predation by saurischians

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Dinosaur Groups - Thyreophora

• Armored ornithischians - began at start of
  Jurassic became common and developed two best
  known forms by end of Jurassic

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Dinosaur Groups - Theropods
Ceratosaurus - Ceratosaurians were the earliest
Theropods (from late Triassic), although this one
is Jurassic Big horns and teeth, curved neck
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Dinosaur Groups - Theropods
Carnosaur? Coelurosaur? 15 feet tall, 40 feet
long, 6 tons in weight Big nose, thighs and
calves adapted for long walks Small eyes and
forelimbs - was this a scavenger or hunter?
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Dinosaur Groups - Sauropods
Late Triassic Long necks, small brains Plant
eaters Had elevated nostrils
This ones Diplodocus
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Dinosaur Groups - Hadrosaurs
Duck-billed plant eater - legs indicate it was a
fast runner (similar in size and shape to modern
runners like horses and ostriches). Crest on
head may have been breathing related or for
making sounds.
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Dinosaur speeds

• Normally recreated from footprint sets, looking
  and distance between prints and depth and shape
  of print
• Fastest found so far was probably about 25 mph
  for a medium-sized theropod
• Very difficult to tell how fast things were

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Dinosaurs and Birds

• Birds are technically dinosaurs
• Remember, pterosaurs werent technically
  dinosaurs
• If birds are dinosaurs, and dinosaurs are
  reptiles, then
• Yes, birds are technically reptiles

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Birds and Dinosaurs

• What group of dinosaurs is most bird-like?
• Theropods - small, carnivorous, fast running (but
  these are saurischians, not ornithischians yes,
  the hips are wrong)
• Within the theropods, the coelurosaurs are among
  the most bird-like
• Coelurosaurs have long arms and big hinged
  ankles. This reduces rotation of the ankle and
  helps running.

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Coelurosaurs
Deinonychus (terrible claw) 10 feet long, 180
lbs, striped (well, could be)
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Coelurosaurs

• Coelurosaurs are a hotly-debated group whose
  membership is not always clear.
• There are many closely related species, but many
  lack key characteristics for coelurosaurs

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Bird ancestors

• Within the Coelurosaurs, there are two
  sister-groups, the Dromaeosauridae (raptors) and
  Aves (birds)
• Both were thought to have a common ancestor
  (possibly a Dromaeosaurid) sometime in the
  Jurassic

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Dromaeosaurs (the Raptors)
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Dromaeosaurs

• Ranged from small (dog-sized) to big
  (limousine-sized)
• Probably hunted in packs (lots of fossils found
  near big prey fossils)
• Lots of claws and teeth, including huge talon on
  one digit of forelimbs
• Stiff, muscular tail for good balance - means
  definitely two-legged

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Dromaeosaurs

• Probably not too fast (they have big thigh bones)
  but may have been very good leapers with the
  ability to attack with all four legs
• Velociraptors - found in a few places from late
  Cretaceous - not as big as in Jurassic Park, but
  other raptors were possibly as big

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Ornithomimidae - bird mimicsOstrich-like
dinosaurs
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True Birds (Aves)

• Archaeopteryx long thought to be a bird ancestor
• Still hotly debated
• Ground-Up vs. Trees-Down models of flight
• This one is Trees-Down

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Archaeopteryx
This one is a Ground-Up representation - they
could have started flight with long
leaps Archaeopteryx is somewhat advanced, and
could have made some longish flights, but likely
not really well or all day.
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Archaeopteryx with no artists interpretation -
(note the feathers!)
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Feathers

• Feathers are obviously good for flight
• Feathers are also good insulators
• Its not clear which property was the impetus for
  their evolution - Archaeopteryx might well have
  just been trying to keep warm.

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Timing of Birds

• Birds dont fossilize well - they have weak,
  light bones that are often hollow.
• From 1990-1995, the number of known bird fossils
  doubled.
• When did they start?
• Archaeopteryx is from Late Jurassic
• There were lots of birds, flying and flightless,
  by the end of the Cretaceous, including members
  of modern groups

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Timing of Birds

• Lots of bird diversification in the Cenozoic,
  although most fossils are incomplete.
• By the Early Oligocene (35 Ma), most modern bird
  groups had arrived.
• There were unusual forms, e.g. phororhachids from
  South America - present for much of Cenozoic

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Timing of Birds

• Controversy -Protoavis from Late Triassic
  possibly chimeric
• This would move back bird evolution about 80
  million years to the earlier parts of the
  Mesozoic, and mean they evolved from thecodonts
• Not everybody thinks this is a real bird,
  although its discoverer (Chaterjee) claims it is
  closer to modern birds than Archaeopteryx is
• Birds have lots of fans - creates interest

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Protoavis?
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Protoavis?
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Warm blooded vs. Cold blooded Dinosaurs...

• Definitions
• Endothermic creates heat from inside
• Ectothermic absorbs heat from outside
• Homeothermic maintains a constant internal
  temperature
• Poikilothermic temperature fluctuates depending
  on outside conditions

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Evidence for endothermic dinosaurs

• Fast things need to have heat available. Many
  dinosaurs appear to be fast-moving.
• Today, endotherms normally outcompete ectotherms.
  Since dinosaurs coexisted with known endotherms,
  they must also have been endothermic.
• Dinosaurs were upright walkers with legs below
  their bodies - typical of endotherms

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Evidence for endothermic dinosaurs

• Dinosaurs had big brains, and endotherms tend to
  have big brains (but not always, and brain size
  is correlated with other things, too).
• Ectotherms arent usually found at high
  latitudes, and dinosaurs were (but it was warmer)
• Endotherm predator/prey ratio is usually low, and
  dinosaur ratios match mammals

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Evidence for endothermic dinosaurs

• Dinosaurs were big and had large, complex hearts.
  Complex heart matches modern endotherms.
• Dinosaurs were ancestral to birds, and birds are
  endotherms.
• Endotherms tend to grow fast, and dinosaurs were
  big (but who knows how long they lived?
• Dinosaur bone structure matches modern endotherms
  better than modern ectotherms

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Evidence for ectothermic dinosaurs

• Dinosaurs were huge - could have been effectively
  homeothermic w/o endothermy
• Dinosaurs were huge - couldnt possibly have been
  endothermic because theyd burn up.
• Mesozoic was warm - dinosaurs didnt need to be
  endothermic
• Ectotherms tend to be scaly, and dinosaurs were
  (but so are birds!)

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Evidence for ectothermic dinosaurs

• Some dinosaurs show lines of arrested growth
  (LAGs) in bones. Modern endotherms dont have
  LAGs (unless stressed), but modern ectotherms do.
• Dinosaurs didnt have respiratory turbinates -
  bony structures at front of nasal cavity which
  are covered in mucus, which modern endotherms
  have.

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Five current thermal hypotheses (from UCMP)

• Dinosaurs were complete endotherms, just like
  birds, their descendants.
• Some or all dinosaurs had some intermediate type
  of physiology between endothermy and ectothermy.
• We know too little about dinosaurs to hazard a
  guess at what their physiology was like.
• Dinosaurs were mostly inertial homeotherms they
  were ectothermic but maintained a constant body
  temperature by growing large. Small dinosaurs
  were typical ectotherms, maybe with a slightly
  elevated metabolic rate.
• All dinosaurs were simple ectotherms, enjoying
  the warm Mesozoic climate. But that's okay many
  ectotherms are quite active, so dinosaurs could
  be active, too.