Dinosaur Metabolism
Endothermy or
Ectothermy?
“Ask, and knowledge will be yours”
I. Temperature Control in Vertebrates
A. Three general features of temperature
control systems:
too hot or too cold
1. a source for body heat
2. a way to conserve heat
3. a way to get rid of excess heat
and DNA &
proteins do not
function correctly
B. Importance of temperature control systems:
1. allows the body to maintain an internal
temperature suitable to keeping the organism
alive
2. Muscles (for movement) only function at
proper temperature.
II. Two Models for Temperature Control
A. Ectothermy (“cold-blooded”)
1. an internal body temperature (only
slightly lower than “warm-blooded”
animals) that varies with external
(environmental) conditions due to a slow
metabolism
2. example: reptiles
B. Endothermy (“warm-blooded”)
1. a relatively high, constant internal body
temperature that is regulated internally to
a fast metabolism
2. example: mammals
Metabolism:
the rate that
energy is
obtained
from food.
III. The Debate: Endothermy vs.
Ectothermy
Were dinosaurs ectothermic or endothermic? Here
are some of the arguments:
A. There is evidence that suggests that dinosaurs
had physical characteristics that are similar to
those of endotherms:
1. large rib cage  large heart (needed to
circulate oxygen to fast-working muscles)
2. fast growth rate  required to grow so big
3. could live in cold regions (tundra) 
requires high internal body temperature
III. The Debate (continued)
4. trackway speeds  modern endotherms
5. high predator to prey ratio  endotherms
require more food than ectotherms
6. hip structure supports upright posture 
allows for higher levels of activity
7. holes in the skull, feathers (maybe) and other
anatomy like birds (endotherms)  may be to
get rid of excess heat, insulate needed heat
8. Dinosaurs seem to exhibit parental care 
usually only endotherms can afford this energy
expenditure
III. The Debate (continued)
B. There is evidence that suggests that
dinosaurs had physical characteristics that
are similar to those of ectotherms:
1. Mass homeothermy/ Gigantothermy: Large
objects retain heat longer than small objects
of similar composition  theory states that,
although large dinosaurs were ectothermic,
they were able to maintain relatively high,
constant, internal temperatures because of
their size.
2. Lacking holes in nasal passages (turbinates)
 like reptiles (ectotherms)
III. The Debate (continued)
3. Predator/prey ratio  Athough fossil record
supports endothermy, fossilization is a
chance process and record is incomplete.
4. Lung structure may not have allowed for
sufficient oxygen intake  Ectotherms need
less oxygen
5. Bone formation  Similar to active present-day
reptiles (ectotherms)
6. Large dinosaurs may not have been able to
consume enough food to support endothermy
 ectotherms require less food