ever existed in the wild. (Natives keep dogs on Komodo, but these
canines are a wretchedly scrawny lot, hardly a threat to the ora.)
80 I THE CONQUERING COLD-BLOODS: A CONUNDRUM
The conclusion is inescapable: Giant predator lizards can't
evolve in the presence of big mammal predators. So the lesson is
that mammals suppress much of the evolutionary potential of
modern lizards. Is the Komodo dragon a good working model of
how dinosaurs succeeded? Absolutely not. Dinosaurs suppressed
the evolutionary potential of mammals, not the other way around.
And dinosaurs carried out this suppression everywhere, on all the
continents, not merely on a few tiny tropical isles. Dinosaurs suc-
ceeded where Komodo dragons fail.
Crocodiles today teach much the same lesson concerning the
limitations of reptiles. They certainly are dangerous to big mam-
mals, but croc hunting tactics are yet another admission of reptile
inferiority in direct confrontation. Nearly all the large mammals
killed by Nile crocodiles are caught near the water's edge. Mod-
ern crocodiles don't go hunting much over dry land, and don't
challenge mammals in the role of terrestrial meat-eater out on the
savannah or in the woodlands. Croc tactics are variants of the ba-
sic reptilian theme: avoid confrontation with big mammals on land,
ambush from special sites that give a reptile an edge. Their low
metabolism allows crocs to stay underwater much longer than a
mammal or bird could, and thus tropical rivers and streams have
remained the locales for an evolutionary proliferation of big croc-
odilian predators all through the Age of Mammals. But on land,
crocs don't score. (There was a mammal-killing croc on land in the
Eocene Epoch [forty million years ago], but it was rare except in
swamps.)
All these facts of modern reptilian failure are damaging to the
orthodox theory of dinosaurs, which consists of one central credo:
Dinosaur metabolism was nothing unusual, merely the standard
lizard-style system blown up to accommodate multi-ton monsters;
dinosaur hearts and lungs were as inferior to the big mammals' as
giant tortoises' were. If this credo is correct, then the dinosaurs'
successes and failures should follow the identical ecological pat-
tern to that of the modern Reptilia. But the entire history of the
dinosaurs is totally and indisputably the opposite of the tortoise-
lizard—croc—turtle history today. Let's summarize the ecological box
scores:
Modern reptiles score very high, higher than mammals, as
small-sized species. But dinosaurs produced no really small
species, not one with an adult weight of less than two ounces
DINOSAURS SCORE WHERE KOMODO DRAGONS FAIL | 81
(the average for lizards), and very few of less than ten pounds.
So dinosaurs failed miserably where modern reptiles succeed
magnificently.
Modern reptiles dominate the role of large freshwater pred-
ator. But dinosaurs didn't produce any swimming predators at
all. All the dinosaurian meat-eaters— Tyrannosaurus, Allosau-
rus, and their ecological colleagues—were basically dry-land
types. Again, dinosaurs failed where modern reptiles suc-
ceeded.
Modern reptiles and their cold-blooded cousins the Am-
phibia score very high as small freshwater predators—the lakes
and streams abound with little swimming frogs, snakes, and
turtles. But not one dinosaur was specialized for this type of
role. Yet again, dinosaurs failed in roles where modern rep-
tiles and amphibians succeed.
Where cold-bloods score—small
land-living species. Mammals do
well as small land species—they
score 2,400. Cold-bloods do even
better, breaking the 6,000 species
mark.
82 I THE CONQUERING COLD-BLOODS: A CONUNDRUM
Where cold-bloods score—
small species in freshwater.
Only 50 small mammal
species make their living in
streams, lakes, and ponds.
But nearly 1,300 species of
cold-blooded reptile and
amphibian fill out these
ecological roles.
Where cold-bloods score—
big-bodied species in
freshwater. There's only 1
really big mammal today in
the semiaquatic niche—the
hippo. But there are 15
crocs, turtles, and snakes in
this ecological category.
Modern reptiles fail nearly completely as big, active land
predators wherever land predators roam, and mammals clearly
suppress the evolution of big Komodo dragon-type hunters.
But dinosaurs excelled at being big, land predators, and the
dinosaurs suppressed the evolution of large mammals. There-
fore, dinosaurs succeeded where modern reptiles fail.
Modern reptiles can evolve large body size only if they pos-
sess special adaptations—tortoises have their armor and giant
snakes their stealthy shape and habits. But only a few dino-
saurs were heavily armored, and every dinosaur had relatively
long legs. Dinosaurs didn't slither about, trying to hide. They
succeeded gloriously as big, active land critters, roles where
the Reptilia fail.
In the presence of these facts, is there any way of saving the
orthodox theory of dinosaurs? Can the idea of Tyrannosaurus and
Brontosaurus as giant cold-bloods be salvaged? A number of pa-
leontologists believe so. They rest their belief on a theory called
"mass homeothermy." This theory maintains that dinosaurs suc-
ceeded as cold-blood reptiles, and didn't require a high metabo-
lism because they kept their body temperatures high and constant
simply by evolving gigantic body size. "Homeothermy" literally
means constant temperature, and "mass" refers here to body mass.
In a word, mass homeothermy means keeping warm by being huge.
Yale Professor Richard Swann Lull was the first to spell out this
Where warm-bloods score—big land-living species.
There are 100 or more mammal species today that
reach a hundred pounds, but only 5 reptiles.
How big reptiles cope with big mammals. During the Age of Mammals, big
cold-blooded reptiles evolved four different ways of surviving: a) Live on a
remote island too small for big mammals (the Komodo Dragon took this
route); b) Evolve a cryptic, camouflaged body form (giant pythons and boas
are examples); c) Evolve stout body armor (giant tortoises); d) Evolve aquatic
habits in order to stay under water much longer than a mammal can (a tactic
used by big crocodiles and turtles). Which of these four methods did big
dinosaurs use? Answer—e) None of the above.
idea, back in the 1920s, though the general notion had been sug-
gested long before. The idea is popular because it focuses on ecol-
ogy's most important working principles: The principles of how
the performance of every bodily organ, from brains to intestines,
is altered by the ebb and flow of body heat, and of how body size
controls the way in which bodies gain a
nd lose heat.
Mass homeothermy recognizes, quite correctly, that "good
reptiles" and "good mammals" have totally different solutions to
the problems of heat. The Reptilia have a fundamentally laid-back,
nonconfrontationist approach to ecological action and reaction.
Mammals, on the other hand, are aggressive and compulsive about
food, and seem positively frenetic compared to their reptilian
How cold-bloodedness works. When the sun's rays are warm but not too hot,
the ten-pound lizard's blood is every bit as warm as the ten-pound pig's. But
when the sun's rays are blocked by clouds and rain, the lizard's metabolism is
much too low to keep its body temperature up and its mental and physical
condition slips into a somnolent torpor. If the sun is too hot, the lizard can't
sweat or pant the way a mammal or bird can and the poor lizard's brain heats
up until it addles.
86 | THE CONQUERING COLD-BLOODS: A CONUNDRUM
neighbors. Consequently, reptiles have very low yearly metabolic
needs compared to most mammals' and, on average, a reptile doesn't
need to find food every day.
A three-ounce mammal (chipmunk size) has to scurry about
every day to gather nuts and berries to stoke its metabolic fur-
nace. The mammal therefore is forced by its metabolism to be a
confrontationist; it must go out and confront the weather and
predators and competitors daily. But a three-ounce lizard can stay
tucked snugly in its burrow for weeks, waiting until all is safe be-
fore it scuttles out to forage for food. High metabolism does give
the chipmunk some advantages. The constant supply of body heat
lets the mammal keep its temperature high and constant most of
the time despite fluctuations in the weather. Everything else being
equal, constant body temperature is beneficial because enzymes—
the chemicals that keep bodily processes working—reach peak
output within a narrow range of temperatures. And so perfect
homeothermy allows evolution to fine-tune any creature's phys-
iological mechanisms.
Hot-blooded metabolism buys freedom in time and space. If a species has a
high heat production, it can forage around for food at peak efficiency in the
shade. But a cold-blood must shuttle back and forth, basking in the sun to
warm up before chasing prey in the shade.
DINOSAURS SCORE WHERE KOMODO DRAGONS FAIL
87
If body temperatures fluctuate wildly, on the other hand, then
internal body chemistry can never settle into an optimal mode. If
tissues get too cold, metabolism will slow to stalling speed. If tis-
sues overheat, the enzymes can denature and the creatures' in-
nards addle (the central nervous system, for example, is the most
sensitive in humans; brain death takes only a few dozen minutes
at 108°F).
How warm-bloodedness works—Part 1. Typical mammals and birds have
super-high body-heat production nearly all the time. When the weather is
warm, blood flow to the skin increases, so more body heat escapes into the
air. When the weather is cool, blood flow to the skin decreases, so more of
the body heat is kept in the body.
88 | THE CONQUERING COLD-BLOODS: A CONUNDRUM
A useful rule to help us understand all this is that Q 1 0 = 2,
which means that for every ten-degree change in body tempera-
ture (measured in Centigrade), the rate of a physiological process
changes twofold. According to this formula, a lizard which enjoys
peak enzyme activity at 38° Centigrade (normal human body tem-
perature) would suffer a decline to one half of optimal rates at 28°C
and to one quarter at 18°C A chipmunk, with its high metabo-
lism, can keep its internal chemistry operating optimally even when
its habitat cools. Therefore the chipmunk can run at top physio-
logical efficiency even when it spends hours foraging in deep shade
and in other locales lacking warmth. The three-ounce lizard is much
more severely constrained geographically. Its metabolism isn't strong
How warm-bloodedness works—Part 2 . Birds and mammals have extra
physiological adaptations for extreme weather. If it gets too hot, sweating or
panting will increase the heat loss from the body. If it gets too cold, shivering
will increase the body-heat production two or three times.
DINOSAURS SCORE WHERE KOMODO DRAGONS FAIL | 89
enough to keep its body temperature constant in cool, dark places.
High body heat also gives the chipmunk more flexibility in time
than its lizard neighbor. The mammal can keep its temperature high
even during the cool parts of the day, during the early morning
and evening of summer, or all day during winter. Yet the reptile
has some compensating advantages. Since it doesn't have to fuel
its metabolic fires as continuously, it can afford to wait until con-
ditions are just right before it risks confrontation with dangerous
neighbors.
These are the principles that define the boundaries of the
reptile's modern ecological successes: physiological guerrilla war-
fare, conflict by hit-and-run, wait-and-hit. These reptile rules work
perfectly for relatively small species. Small snakes and lizards can
hide in hollow logs, burrows, or up in the trees when enemies
threaten. Eight thousand living species of land reptile and amphib-
ian follow variants of the wait-and-hit strategy. All are small enough
to stay protected in their habitat lairs, waiting for the opportune
time to emerge. There's nothing cowardly or disreputable about
this reptile strategy; their physiological equipment simply repre-
sents an alternative mode of adapting compared to the constant
hyperactivity of most mammals.
Wait-and-hit strategy works only if the reptile has a safe place
to wait. And there's the great problem for big land reptiles: find-
ing a hole to hide a two-hundred-pound lizard is difficult. Ko-
modo dragons seek caves or other lairs, but the bigger the lizard
grows the fewer the lairs that fit. Tortoises solve this problem by
carrying their own cave with them wherever they go. No other
big reptile has solved the problem so well.
But where could a two-ton Allosaurus hide? The theory of mass
homeothermy maintains dinosaurs didn't need such holes to hide
in because they were so big their bodies never cooled to danger-
ously low temperatures. Two laws concerning body heat and body
size serve as the foundations for this argument. First, bigger bod-
ies produce less body heat per pound per hour. Second, bigger
bodies lose less body heat per pound through the skin. Together,
these two laws mean that it's easier to keep warm in a big body
than in a little one.
Physiologists describe these laws as examples of the "mouse-
to—elephant phenomenon." All through the animal kingdom, the
90 I THE CONQUERING COLD-BLOODS: A CONUNDRUM
Big or little, every cold-blood puts out much less body heat than a warm-
blood of the same size. If you have a lizard warmed up to 98.7 degrees F, its
body heat is about one fourth as high as a typical mammal of the same body
they get. If we increase body size ten thousand times, the heat production
drops to one tenth.
production of body heat drops in a very regular way as body size
increases. A simple mathematical shorthand defines this phenom-
enon: M = kfW~' ;A M is metabolic heat production, W is body
weight, and k is a constant. A bunny weighs about one pound; a
five-ton elephant is 10,000 times heavier. So the elephant's pro-
duction of body heat is (lO^OO)'4 times less per pound, or ten
times less per pound than that of the bunny.
An old saw perfectly illustrates this mouse—to—elephant phe-
nomenon: "What will keep you warmer on a cold night at the zoo,
snuggling up with a five-ton bull elephant, or with 10,000 bunnies
who altogether weigh five tons?" Answer: The bunnies. They put
out ten times as much heat.
Producing less heat per pound, however, doesn't mean a big
animal is colder than a small one—just the reverse. When a ver-
tebrate body is at rest, it loses heat to the environment mostly
through its skin. If it has a lot of flesh per square inch of skin, it
saves heat. If size goes up, the skin area per pound of flesh goes
DINOSAURS SCORE WHERE KOMODO DRAGONS FAIL
91
down. Hence the big animal keeps warmer more easily because
the area of its skin surface is less, relative to its heat output. (The
mathematical shorthand for this corporeal geometry is A = k/W~'A;
A is skin area per pound, W is body weight, and k is a constant.
This relationship holds true only as long as body shape stays sim-
ilar. So we can't use the same formula for snakes and turtles.)
Now let's compare the bunny to the bull elephant again. The
elephant is 10,000 times heavier than a bunny. Bunny and ele-
phant have roughly similar shapes—a compact body and one set
of skinny protuberances (trunk for elephant, ears for bunny). The
elephant has much less skin per pound—about 22 times less than
the bunny. So the elephant has proportionately much less skin area
through which to lose its body heat. The two mouse—to—elephant
thermal laws therefore combine to give the big animal better heat-
Robert T Bakker Page 9
