cles (the temporals) pull upward and backward, their combined
crossing action preventing stress from building up in our jaw joint.
Every time we tackle an especially tough steak, we should harbor
a little thought of thanks to our cynodont ancestors.
No doubt that the Triassic protomammals were the best and
the brightest ever produced by the protomammals. And, in sharp
contrast to their pervasive bias against any notion of warm-blooded
dinosaurs, orthodox paleontologists have been more than willing
to accept the idea that advanced cynodonts were warm-blooded
creatures. No one voiced surprise when Armand de Ricqles an-
nounced he had found mammal-type bone texture in the Triassic
dicynodonts and cynodonts. Orthodoxy had always maintained, after
all, that advanced protomammals were physiologically far more
sophisticated than the reptiles were.
All these assumptions might lead one to believe these dog-
faced protomammals exercised unassailable hegemony over their
ecosystem. But that was not the case. The biggest, strongest, most
dangerous predators of the Early Triassic were not cynodonts or
any sort of protomammal at all. That role belonged to those crim-
son crocodiles, the shock troops of the rival empire. They attained
a weight of half a ton, and were armed with dinosaurlike heads
three feet long, and saw-edged teeth.
418 | DYNASTIC FRAILTY AND THE PULSES OF ANIMAL HISTORY
Orthodox paleontologists and mammal loyalists cannot es-
cape the meaning of the ecological takeover by these crimson
crocodiles. Before they evolved, the honors for top predator had
gone to protomammals—the anteosaurs of the Kazanian, the gor-
gons of the Tartarian. After the Tartarian mass extinction, the role
of top predator lay open for the taking, for whichever group was
best adapted to claim it. Filling that role is an ecological challenge
like no other, because the competition is bloody and merciless.
Top predators struggled for hunting territory and for scavenging
rights over the biggest carcasses. Natural selection is therefore es-
pecially unforgiving when it comes to top predators—the survi-
vors will be the fastest, meanest, and most efficient species every
time.
Now, even though the cynodonts were among the fastest and
most efficient predators available at the opening of the Triassic
Period, there can be no doubt that the crimson crocodiles even-
tually seized undisputed possession of the top predator niches. Not
only did the early archosaurians fill the top predator roles, they,
their descendants, and close relatives (as a group, formally known
as the Thecodontia) usurped more and more of the medium and
small predatory niches as well as the Triassic Period went on. No-
where else does the fossil history of life display such a clear-cut
case of evolutionary imperialism; as the archosaurs' reign ex-
panded, the cynodonts' contracted. By the Mid Triassic, the cyn-
odonts had retreated to small and medium-small predators and to
herbivores. Meanwhile, the thecodonts filled the ecosystem with
fox-sized, wolf-sized, lion-sized, and polar bear-sized carnivorous
species, from a few pounds to half a ton as adults.
By Late Triassic times, the erythrosuchians' descendants had
branched out into two distinct river-and-lake groups of fish-eaters.
The proterochampsids, with their flat heads and long snouts, pro-
pelled themselves through the waters by means of their large hind
legs. The heavily armored phytosaurs, on the other hand, swam by
virtue of their crocodile-like tails. The crimson crocodiles' descen-
dants also developed into an herbivorous group, the aetosaurs. They
developed body armor top and bottom, with extra protection in
some species of curved, bony spikes over the shoulders. For their
time, the aetosaurs were the best-protected land animals that had
evolved anywhere.
Working on my senior thesis at Yale, I did a great deal of
THE KAZANIAN REVOLUTION: SETTING THE STAGE FOR THE DINOSAURIA | 419
Early Triassic class warfare: A pair of dog-faced cynodonts, Cynognathus, are
threatened by two 1,000-pound Erythrosuchus.
meditating about the success of the erythrosuchians. Could it be
that Erythrosuchus and all its relatives had had superior adaptive
equipment? Had the thecodonts in fact been warm-blooded? If they
had been, the evidence would have to come from the microtex-
ture of their bones and their predator-to-prey relations. And both
forms of evidence came tumbling into the laboratory during the
1970s. Armand de Ricqles found mammal-type bone texture in
Erythrosuchus itself and in its close kin. I counted Erythrosuchus
specimens in museums from Cape Town to Berkeley. The case for
high metabolism was every bit as conclusive as it was for the ad-
vanced protomammals.
There was therefore nothing at all paradoxical about the suc-
cess of the crimson crocodiles. This vigorously evolving group had
wrested control of the predatory roles from the protomammals
because of the erythrosuchian anatomical equipment, which had
been equal to, or better than, the best produced by the two-
tuskers or the dog-faces. This was an heretical conclusion indeed
because the erythrosuchians and all the Thecodontia were uncles
of the dinosaurs, the evolutionary cousins of the direct ancestors
of the true Dinosauria. There was the spark of dinosaurness about
everything the thecodonts did, and the earliest true dinosaurs, of
all sorts, shared many of the anatomical features of the Thecodon-
tia. Most notable of these were the extra openings in the side of
the snout and in the lower jaw that had been the trademarks of
Erythrosuchus and other early thecodonts. All the early dinosaurs'
skulls were characterized by the loose, open construction directly
modeled on the thecodonts. Without any doubt, the dinosaurs had
inherited fundamental adaptive equipment from thecodont ances-
tors, and they owed much of their success to the momentous de-
velopments among the first crimson crocodiles of the Earliest
Triassic.
All the many thecodont families went extinct at the end of
the Triassic. But their end corresponded with the beginning of the
first great Age of Dinosaurs. As the Jurassic Period began, the ter-
restrial ecosystem was once again riddled with unfilled niches, and
into these ecological opportunities streamed a horde of new spe-
cies. In Late Triassic times the dinosaurs had been a minority group,
but in the Jurassic every single large land predator and herbivore
role was filled by their newly evolving species.
422 | DYNASTIC FRAILTY AND THE PULSES OF ANIMAL HISTORY
When we place the history of the dinosaurs into its proper
context, therefore, the high metabolic adaptations of the Dinosau-
ria are not at all surprising. They were the inevitable results of
evolutionary processes that had begun long before the first true
dinosaur appeared. Dinosaurs weren't the first dynasty of warm-
bloode
d creatures. Neither were they the first to have a fast-paced
evolutionary tempo, punctuated by sudden mass extinction. The
world's ecosystems had been shaken out of their plodding, cold-
blooded rhythm long before the dinosaurs made their entry into
Two lines of the crimson-croc takeover: the armored aeotosaur Desmatosuchus
and a big-headed rauisuchid predator. Both from the Late Triassic.
the evolutionary race. The Kazanian protomammals were the pi-
oneers of high metabolism, revolutionizing the rules of competi-
tion and predation in the epochs of the Late Permian. Once high
metabolic adaptations had been introduced onto the ecological stage,
no group of large land vertebrates could hope to achieve domi-
nance without such physiological equipment. So when the first di-
nosaurs began elbowing their way into the roles of large predator
and herbivore late in the Triassic Period, they were simply em-
ploying the same strategy for success that had been followed by
their predecessors of the Early Triassic, and by the Tartarian pro-
tomammals before that, and by the Kazanians before that.
The untenable nature of orthodox views about cold-blooded
dinosaurs stands revealed in the context of this progression from
the Kazanian to the Late Triassic. If dinosaurs were 100 percent
cold-blooded, with a metabolic system no more sophisticated than
a lizard's, then the Age of Dinosaurs amounted to an inexplicable
Age of Throwbacks, a monumental step backward in the progres-
sion of life on land, a return to the slow-motion conditions of the
Coal Age. It makes no historical sense to believe the dinosaurs
were cold-blooded. All the fabric of fossil evidence comes to-
gether to weave a coherent story of an unbroken succession of
warm-bloods following one another down through the ages, from
the Late Permian, straight through the entire Mesozoic Era—the
Triassic, Jurassic, and Cretaceous—and finally, consistently, into our
own Age of Mammals.
424 | DYNASTIC FRAILTY AND THE PULSES OF ANIMAL HISTORY
21
THE TWILIGHT OF THE
DINOSAURS
T he mass murder that marked the end of the Cretaceous Period
seems to attract all manner of solutions. Perfectly respectable
scientists, who pride themselves on their caution when dealing with
their own specialty, indulge in the wildest flights of fancy when it
comes to cracking the mystery of the Cretaceous killer. I keep a
file of published "solutions." Among its contents, it is suggested
the dinosaurs died out "because the weather got too hot"; "be-
cause the weather got too cold"; "because the weather got too dry";
"because the weather got too wet"; "because the weather became
too hot in the summer and too cold in the winter"; "because the
land became too hilly"; "because new kinds of plants evolved which
poisoned all the dinosaurs"; "because new kinds of insects evolved
which spread deadly diseases"; "because new kinds of mammals
evolved which competed for food"; "because new kinds of mam-
mals ate the dinosaurs' eggs"; "because a giant meteor smashed into
the earth"; "because a supernova exploded near the earth"; "be-
cause cosmic rays bombarded the earth"; or, "because massive
volcanoes exploded all around the earth."
It has always seemed a bit strange to me that otherwise sober
scientists should leap to conclusions about the extinction of the
dinosaurs. Perhaps, as Zorba the Greek told us, scientists and
nonscientists alike are seduced into believing far-fetched solutions
because we all need a little madness. The events in question had
THE TWILIGHT OF THE DINOSAURS
425
Sea-monster victims of Cretaceous extinction:
The great sea lizard Mosasaurus and the
plesiosaur Dolichorhynchops.
no eyewitnesses and were heroic in size, larger than life, unlike
anything we see in our modern world. As a consequence, we are
lured, attracted by the notion that mysteries of heroic scale re-
quire solutions of equally heroic scale, solutions totally different
from the mundane, day-to-day events we experience all around us.
I am firmly convinced that all the great mysteries—the Mayan
426 | DYNASTIC FRAILTY AND THE PULSES OF ANIMAL HISTORY
Pyramids, Stonehenge, the stone heads on Easter Island, and the
dinosaur extinctions—are solvable. In fact, I believe most have al-
ready been solved long ago. But the solution is usually so obvious,
so nonfantastic, that its very mundaneness comes as a jolt. So what
is the obvious, mundane solution to the great mass murder of the
Cretaceous? Let us build up the evidence piece by piece, before
we speak the name of the murderer.
The attempt to solve the crime of mass extinction begins by
encountering one of the basic problems in criminology: the reli-
ability of circumstantial evidence. Scientists have occasionally hoped
dinosaur carcasses would yield direct evidence about the agent of
death. In the 1920s, one paleontologist concluded the duckbills
had all died from some ghastly poison because their skeletons were
contorted into what looked like postures of agony. But it turned
out those skeletons were contorted—the neck twisted upward and
backward—because this was the normal posture for any corpse since
the muscles and tendons of the neck contracted after death. And
in fact, fossil skeletons seldom if ever yield a clue about the cause
of death at the end of the Cretaceous or any other time. Thin sec-
tions from dinosaur bones usually show no obvious signs of pa-
thology. But even this is not conclusive since most fatal diseases
leave no clear mark on bone.
The only clues for finding the murderer^ then, are those re-
siding in the circumstantial evidence—the conditions at the scene
of the crime. The problem with such evidence, however, is the
great difficulty in separating the relevant facts from the mass of
irrelevant details. A very standard procedure adopted by those at-
tempting to solve the mystery is to pore over the many details we
know about the circumstances surrounding the final death of the
dinosaurs in North America, with scattered bits and pieces of in-
formation from elsewhere in the world. The hypothesis here is that
some shift in the habitat must have doomed the dinosaurs. So in-
vestigation must concentrate on what changed at the end of the
Cretaceous. The crippling flaw in this method of approach is that
habitats in the world are never really stable, they are always changing
through time. If we look for evidence of environmental change
anywhere in geological history, therefore, we are certain to find it.
As an example of the problems inherent in this method of
dealing with the circumstantial evidence, paleontologists inter-
THE TWILIGHT OF THE DINOSAURS I 427
ested in plants have found that winters became cooler at the
end of the Cretaceous. As a result, many geologists concluded the
dinosaurs died from climatic chill. But such a judgment was
premature. Perhaps the
chilling trend was only an innocent envi-
ronmental bystander, a change in habitat that just happened to oc-
cur at the same time the real agent of death was killing off the
Dinosauria. It cannot be considered guilty merely because it was
present at the scene of the crime.
The single most important first step for judging the evidence
about the mass extinction is unfortunately the one usually ig-
nored: the search for a repeated pattern through time. All too often,
the extinction of the dinosaurs is viewed as a single, isolated out-
break of evolutionary mayhem, an ecological St. Valentine Day's
Massacre inflicted upon the denisons of the Cretaceous plains and
forests. If the extinction were indeed a unique, never-repeated
event, then it would be nearly impossible to sort out the irrele-
vant coincidences from the true trail of the killer. But if the true
culprit was a repeat killer that struck the ecosystem again and again
all through geological history, we would be presented with a far
superior chance of sifting out the irrelevant evidence. Repeated
attacks from the same agent under a variety of circumstances will
eventually reveal a modus operandi, the characteristic pattern of the
criminal.
The first step in solving the mystery of the great Cretaceous
mass extinction, then, is to ask, Were there any others? The an-
swer is a resounding affirmative. Mass extinction struck at the end
of the Permian, when the Tartarian families of gorgons disap-
peared along with their dicynodont prey, and at the end of the
Triassic, when the big two-tuskers on land and the long-bodied
fish-lizards at sea died out. It also struck at the end of the Ju-
rassic Period when many (but not all) lines of dinosaurs died out.
Altogether the stratigraphic record indicates eight sudden mass
extinctions among the dominant families of large, land-dwelling
vertebrates. The most recent occurred only ten thousand years
ago when most of the giant species of mammal—mammoths,
mastodons, super-large camels, saber-toothed cats, and others—
perished.
The next step is to ask whether these mass extinctions follow
any coherent pattern. Again, the answer is affirmative—Baron Cu-
428 I DYNASTIC FRAILTY AND THE PULSES OF ANIMAL HISTORY
Robert T Bakker Page 43