Dinosaurs Fact and Fiction

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Dinosaurs - Fact and Fiction
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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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Dinosaur Groups - Ornithischians
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Dinosaur Groups - Saurischians
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Dinosaur Groups Ceratopsians (Subgroup of
Ornithischians)
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
Theropod ?

• What group of dinosaurs is most bird-like?
• Theropods - small, carnivorous, fast running (but
  wait, you say - 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.

Coelurosaur ?
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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 that 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
• This would move back bird evolution about 80
  million years to the earlier parts of the
  Mesozoic
• 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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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.