What Makes a Dino-sore?

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• What Makes a Dino-sore? Calling Him a
  Birdbrain
• Harry Jerison (UCLA)
• lthjerison_at_ucla.edugt

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• In the first graph youll see why dinosaurs
  should feel flattered to be called birdbrains.

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Minimum convex polygons containing presently
available data on living amniotes (mammals,
birds, and reptiles). Adding data on dinosaur
points suggests an extended reptilian polygon
(dashed lines). Earliest bird (Archaeopteryx) is
at lower edge of living birds. Data on dinosaur
genera (estimated body weights and brain
weights) Protoceratops (200kg/28g) Camptosaurus
(400kg/23g), Kentrosaurus (780kg/24g),
Euoplocephalus (1,900kg/41g), Iguanodon
(2,100kg/125g), Allosaurus (2,300kg/168g),
Stegosaurus 3,100kg/22.5g, Edmontosaurus
(6,200kg/200g), Tyrannosaurus (7,400kg/202g),
Triceratops (9,000kg/72g) Diplodocus
(19,000kg/57g), Brachiosaurus (78,300kg/186g).
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• Why is brain size a useful measure? In
  mammals, it estimates information-processing
  capacity. Is brain size similarly useful in
  birds and reptiles? We dont know, but its a
  reasonable guess.

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Edmontosaurus, the first dinosaur brain in the
show.

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• Next, a bad drawing of Edmontosaurus, a six
  ton duck-bill Cretaceous dinosaur from Montana.
  It lived there about 70 million years ago.

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• Next will be Maiasaura,a dinosaur that left
  fossil eggs in Montana, and was about the same
  size and shape as Edmontosaurus. Jack Horner
  (Museum of the Rockies) dug up both dinosaurs.
  He figured that if Maia laid eggs it had to be a
  she, so he gave her a feminine name.

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Maiasaura
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3D scan of a Maiasaura model, which was scaled up
to estimate Edmontosaurus body weight for the
graph.
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Brain-Body Space in Amniotes
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The next dinosaur, Troodon, weighed about 45 kg
and also acted for Spielberg and Lucas in
Jurassic Park III. Its brain is on the next
slide.
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Troodon's brain - an endocast of course -
compared to an ostrich and an albatross endocast.

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When I showed Bill Hodos the Troodon endocast he
thought he saw a suggestion of a Wulst. Here is a
view of the albatross endocast with its prominent
Wulst. Troodon is next.
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Snapshot of 3D image of Troodon endocast.
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The Field Museum in Chicago, talked the Boeing
company into doing a CT scan of their
Tyrannosaurus rex (Sue) skull. Here is what
turned up.

• Endocast and skull of Tyrannosaurus rex. A.
  Dorsal view of endocast. B. CT section olb,
  olfactory bulb area se, sphenethmoid bone orb,
  orbit I, olfactory tract fm, foramen magnum.
  C. Reconstruction of skull from CT scans, showing
  level of CT section of B. (From Brochu, C.
  Journal of Vertebrate Paleontology, 201-6, 2000.
  By permission.)

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• How should we interpret the very large T rex
  "olfactory bulbs" on the endocast? They are at
  least four times the size of the "brain" itself.
  In living birds, the kiwi has the biggest
  olfactory bulbs relative to its brain size, and
  they are about 1/5th the brain volume. The
  turkey vulture's is about 1/10th brain volume.

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• The next slide shows the situation in living
  mammals. The biggest olfactory bulbs (relative
  size) in mammals are no more than about 10 of
  the whole brain. Best guess is T rex's olfactory
  bulbs didn't fill the space for them in its head,
  and its olfaction is interpretable as in living
  vertebrates.

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• We need numbers involving brain size in more
  species. These help us analyze the fossil
  evidence for brain evolution. For many major
  structures in the brain we can estimate sizes
  from gross brain size. The brain hangs together.

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(Adapted from Braitenberg, V. Schüz, A. (1998
1991. Anatomy of the Cortex Statistics and
Geometry. Berlin, Heidelberg Springer.)
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