By Melissa Jayne and Linda Rocha
 Internal heat production through metabolism
 Examples
and
Birds
Mammals
 Obtaining heat from the external environment.
 Examples: Amphibians, insects, and
reptiles.
 “Homeothermy is the maintenance of a constant
temperature independent of external temperatures.”
 According to this hypothesis, dinosaurs were cold-
blooded and had a low metabolism.
 Larger dinosaurs would have had a lower surface area
to volume ratio and were therefore able to maintain a
relatively constant body temperature.
 As body size increases so should body temperature.
 Bakker (1986)
 Only applies to large dinosaurs
 Hypothesis is unable to explain the success of
dinosaurs over mammals.
 Smaller dinosaurs had a high metabolism and
therefore it is unlikely that larger dinosaurs would
have evolved to have a low metabolism.
 Inertial homeothermy does not work in today’s
ecosystems.
 J.F. Gillooly, A.P. Allen, and E.L. Charnov (2006)
 Presented a model that predicted the body
temperatures of dinosaurs using “ontogenetic growth
trajectories obtained from fossil bones.”
 Data on the ontogenetic growth trajectories of eight
different dinosaur species were collected.
 The masses of these dinosaurs ranged from 12kg
(P. mongoliensis) to 12,979 Kg (Ap. excelsus).
 Tyrannosaurus Rex is only 1/12 the size of Apatosaurus
Excelsus.
P. Mongoliensis
T. Rex
This equation is used in a model that predicts the effects of body size and
temperature on growth rate.
G = g0M3/4e0.1Tb
G = Growth rate (Kg day-1)
g0 = Normalization Constant (~ 2 x 10-4 Kg1/4 day-1 )
M = Mass at maximum growth (Kg)
e0.1Tb = Temperature Term (takes into account the biochemical reactions
involved in growth and represents the average activation energy)
Tb = Body Temperature (˚C)
The terms in the previous equation can be rearranged
in order to predict the body temperatures of specific
dinosaur species.
Tb = 10ln(GM-3/4/g0)
P. mongoliensis
M = 12 Kg
G = ~ 1.57 x 10 -2 Kg day-1
g0 = 2 x 10-4 Kg1/4 day-1
By using the data provided above we can solve for T b
Tb = 10 ln[(.0157 Kg day-1 x 12 -3/4kg)/ (2 x 10-4 Kg1/4 day-1)]
T b = ~ 25°C
 According to Parrish, crocodiles are the last living
non-avian Archosaurs.
 Crocodiles are the largest living reptiles and have a
vast ontogenetic size range.
“A plot of the relationship between Average Body Temperature
(°C) and the Logarithm of Body Mass for Dinosaurs and Extant
Crocodiles.”
“ A plot of observed versus the predicted increase in average
body temperature (°C) with body mass for crocodiles.”
 Create and test a model that determines the metabolic
rate of various dinosaurs in order to support or oppose
the inertial homeothermy hypothesis.
 Archosaurs: A group of reptiles represented by modern
birds and crocodilians.
 Ontogeny: the development of an organism from the
fertilized egg to its mature form.
 Bakker, R.T. The Dinosaur Heresies: New Theories
Unlocking the Mystery of the Dinosaurs and Their
Extinction. New York: Kensington Publishing Corp.
1986.
 Gillooly, J.F., A.P. Allen and E.L. Charnov. 2006.
Dinosaur Fossils Predict Body Temperatures. PLos
Biology. 4:1467-1469.
 Gross, L. 2006. Math and Fossils Resolve a Debate on
Dinosaur Metabolism. PLoS Biology. 4:1296.
 Parrish, J.M. 1997. Evolution of the Archosaurs. Farlow
and Brett Surman 191-203
 Ruxton, G.D. 2001. Heat loss from giant extinct
reptiles. The Royal Society. 268:1921-1924.
 Seebacher, F. 2003. Dinosaur body temperatures: the
occurrence of endothermy and ectothermy.
Paleobiology. 29(1):105-122.
 Smith, R.L. and T.M. Smith. Elements of Ecology. 5th
ed. San Francisco: Benjamin Cummings, 2003.
 Terblanche, J.S. 2007. Big Dinosaurs: Hot or Not? The
Journal of Experimental Biology. 210