THEROPODS AS LIVING ANIMALS
ENCEPHALIZATION QUOTIENT (EQ)
- Theropods included the "brainiest" dinosaurs, based on their
encephalization quotient (EQ).
- EQ is calculated as the [mass of the cerebral cortex] / [mass of the total
- This is difficult enough to measure in living animals and is
impossible in extinct ones.
- EQ can also be calculated as the ratio of the estimated brain weight or
volume to the brain weight or volume predicted for a typical animal of that
- The brain mass to body mass or braincase volume to body volume can be
more easily determined in living animals.
- For an elephant:
- Brain mass = 7,500 g = 7.5 kg
- Body mass = 5,000 kg
- the brain to body mass = 0.15%
- For a human
- Brain mass = 1.5 kg
- body mass = 70 kg
- 2.1% of the body is brain
- Braincase volume or mass from recent or fossil skulls can be
calculated using endocranial casts.
- Making Endocranial
- CT Computer
generated endocasts from Harry Jerrison
- A natural endocranial
cast of Allosaurus
- Methods for Estimating Body Volume or Mass
of dinosaurswere discussed in a previous lecture.
- Tyrannosaurus rex
- Brain volume = 500 cm3
- body volume = 6.35 x 106 cm3
- 0.0079% of the body is brain
- Brain volume = 300 cm3
- body volume = 8.55 x 106 cm3
- 0.0035% of the body is brain
- Because larger animals tend to have relatively smaller brain to body
ratios, the effects of size must be corrected.
- Plots of the relationship of brain mass to body mass has been determined
for extant organisms
- There is an allometric relationship for these two variables
- the allometric equation is Y = aXb
- or Log (Y) = b * Log (X) + Log (a)
- Least squares reqression is used to determine the relationship
between two variables. Linear regression fits a straight line
to the data.
- When the logarithm of brain size is plotted on the y axis and the
logarithm of body size is plotted on the x axis, you get a straight line
on regular graph paper.
- Jerrison's brain to body plots
- For mammals and birds
- Expected brain weight = 0.07 x body weight0.67
- For living reptiles and fish
- Expected brain weight = 0.007 x body weight0.67
Hurlburt's brain to body plots
- For living reptiles
- Log (brain mass) = -1.792 + (0.55 x log (body mass))
- The regression lone for modern reptiles was used as the allometric line to
determine dinosaur EQ’s
- EQ's less than 1 plot below the line
EQ’s more than 1 plot above the line
- Theropods EQ’s are more than 1
relative to the reptile line but are less than 1 relative to the mammal line
Using the reptile line,
- Crocodiles have an EQ = 1
- All theropods have an EQ > 1.
- Troodon and Velociraptor, have EQ’s of 5.8,
similar to modern ostriches.
- Other than most ornithopods, all other dinosaurs have an EQ <
- Sauropods have EQ = 0.2
Sexual Dimorphism among Theropods
- Coelophysis, Syntarsus, and Tyrannosaurus among
others exhibit consistent size differences
- This is interpreted as sexual dimorphism.
- Larger forms are thought to be female.
- Crests in dinosaurs such as Dilophosaurus and head ornamentation
such as is present in Ceratosaurus and Allosaurus may have
been foor display.
- Large non-flight feathers such as occur in Caudipteryx may have
been used for mating displays.
- Clutches of about 15 eggs from the late Cretaceous of the Gobi Desert were
initially thought to belong to the primitive ceratopsian Protoceratops.
Oviraptor ("egg thief") was thought to feed upon the eggs
by crushing them in its toothless jaws. The eggs are now attributed to
Oviraptor based on embryos in eggs. An exciting recent
discovers shows apparent brooding behavior by Oviraptor.
- Eggs initially attributed to Orodromeus, a hypsilophodont, are now
attributed to Troodon based on embryos in eggs and from a skeleton of
Troodon found on top of eight eggs.