Some Irreverent Thoughts 
about Dinosaur Metabolic 
Physiology: Jurisphagous 
Food Consumption Rates of 
Tyrannosaurus rex 
M. K. Brett-Surman and 
James 0. Farlow 
It is agreed by all living humans 
that the highlight of the movie juras- 
sic A** (Universal Studio*, 1993) was 
the consumption of the lawyer by the 
true heroof the movie, Tynmnosowna 
rex. This brings up an obvious ques- 
tion: How many lawyers would it take 
to properly feed a captive 7! rex? For- 
tunately science has now progressed 
to the point where this Important 
question can be answered and 
plans made accordingly. 
Two pieces of Information are 
needed: 
(A) The food requirements of a T. 
rex for one year 
(B) The food value of one lawyer 
Following the way that it was por- 
trayed In /umswc Port let us first as- 
sume that our T. rex Is endothermk. 
Let us also assume that our tyranno- 
saur weigh; 10,000 pounds (4540 
kg}?perhaps a bit on the Bght side 
(Farlow et al. 1995), but dose 
enough. 
Farlow (1990; see Fadow 1976 for 
details about the data used) pub- 
lished an equation relating the food 
consumption rate (in watts, or joules/ 
second; that is, the amount of food 
energy needed per unit time) to body 
mass (in kilograms) in living endo- 
therms (mammals and birds): 
consumption rate = 10.96 X 
body man*" 
For a 4540-kilogram T. rex, the 
equation predicts an average food 
consumption rate of 3978.8 joules/ 
second. Because we are interested in 
the time span of one year, we must 
now multiply this result by 3.1536 X 
10*, which is the number of seconds 
in one year (that b, 60 seconds/ 
minute X 60 minutes/hour X 24 
hours/day X 365 days/year?unless 
you are watching golf on T% In which 
case this number is much higher), to 
give us the tyrannosaur's energy 
needs in joules/year. This results in a 
big number 1.2547 X 10" joules/ 
year. 
This gives us the first part of what 
we need to know in order to begin 
rounding up enough lawyers to keep 
our dinosaur content. We must now 
calculate the energy value of one law- 
yer. 
There are three components of 
the food value, In joules, of one law- 
yer (1) the energy value (In joules) of 
1 kilogram of lawyer flesh; (2) the 
number of kBograms (mass) In our 
sacrifdal lawyer; (3) the digestive 
percentage, or assimilation efficiency, 
of a carnivore dgesdng meat?In the 
present case, this Is the percentage of 
the lawyer that actually has food 
value. (We assume that doming, 
briefcase, cellular phone, and pocket 
organizer have no energy value, and 
so these components of an opera- 
tional lawyer will be ignored In our 
calculations.) 
We assume that the energy value 
of lawyer meat, Hke that of other 
animals. Is 7 X 10* joules/kWogram 
(Peten 1983). We further assume that 
our lawyer weighs 150 pounds, or 
68.1 kilograms. 
The assimilation efficiency of 
carnivores eadng meat is about 90 
percent (Golley 1960; this Is much 
higher than for herbivores feeding 
on high fiber forage?as presum- 
ably was the case lor most herbivo- 
rous dinosaurs; see Tiffney, chap. 25 
of this volume). 
The energy value of a single law- 
yer can now be calculated as 
68.1 kg X (7X10* joules/kg) 
X0.9m4J903X 10* joules 
By dividing the yearly energy re- 
quirements of our T. rex by the energy 
value of a single lawyer, we get the 
yearly lawyer consumption that our 
dinosaur would need: 
(1JS47 X 10" joules/year)/ 
(4.2903 X10* joules/lawyer) - 
292 lawyers/year 
The calculations are the same If 
we assume that our tyrannosaur was 
an ectotherm, except that we must 
use an equation relating food con- 
sumption rate to body mass in rep- 
tiles and amphibians (Farlow 1990; 
same units as for endotherms): 
consumption rate * 0.84 X 
mass** 
For a 4540-kilogram T. rex, thb 
equation predicts a feeding rate of 
991.3 watts, which wodo out to 73 
lawyers per year. 
We can see, then, that genetically 
resurrected tyrannosaurs would have 
a far greater predatory impact on the 
lawyer population if they were endo- 
therms than if they were ectotherms. 
This is perhaps a good reason for 
hoping that dinosaurs will turn out to 
have been endotherms. 
References 
Fwkwt |. 0.1976. A conddeadon of the 
trophic dynamics of a Late Creta- 
ceous large-dinosaur community 
(Oldman Formation). Ecology 57: 
841-837. 
Farlow, |. O. 1990. Dinosaur energetics 
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Weishampel, P. Dodson, and H. 
Osmdbka (eds.), 77* Obosoxdo, pp. 
43-55. Berkley: University of CaB- 
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Farlow, |. O.; M. B. Smith; and |. M. 
Robinson. 1995. Body mass, bone 
"strength indicator," and cursorial 
potential of Tyrannosaurus rex. lour- 
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713-725. 
GoBey, F. B. 1960. Energy dynamic: ol a 
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206. 
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