storage drawers in the United States and Canada. The effort to do
so would be incomparably rewarding for both professionals and
the public, if for nothing other than the opportunity of at last
viewing one of the most formidable gastrointestinal systems in the
Dinosauria. From the side, the ankylosaurs and domeheads pre-
sent a tubby appearance—deep ribs arching out from the chest and
belly. Looking from above straight down on the ribs and hips, the
entire hind region from belly to tail was enormously expanded,
nearly beyond the anatomically credible. Ribs became longer from
mid-torso to hips, until the rearmost ribs arched out so far that
the afterbelly must have been wider from side to side than it was
deep from top to bottom. This extra-wide fermenting compart-
ment continued beneath the upper hip bones (the ilia), where the
normally narrow pelvic architecture was transformed into an im-
mensely broad horizontal roof. The ensemble was a dinosaurian
body broadened to twice the usual width through the compart-
ments housing the intestines and colon.
No other dinosaur's gastrointestinal system was nearly so en-
176 I THE HABITAT OF THE DINOSAURS
Guts of a nodosaur
larged relative to the body mass. No mammal or bird possesses
comparable skeletal architecture today. The exact layout of stom-
ach, intestines, and colon in ankylosaurs will never be certainly
known. It is certain however that every leafy bolus received an
extraordinarily thorough biochemical treatment in a long series of
enzyme baths and fermentation vats. The ankylosaur's teeth were
indeed weak, but its beak was strong and sharp-edged. So the an-
DINOSAURS AT TABLE I 177
kylosaur began the process of feeding by stuffing broad mouthfuls
of leaves into its capacious cheeks. Then with its simple row of
teeth it cut the longer leaves and stems a few times, and wadded
up the pieces between its cheeks and tongue into a coarse bolus.
The entire ball passed down to the superenlarged gastrointestinal
chambers. Now, the coarsely chopped wad was broken down by
successive biochemical assaults. The huge compartment for the
colon at the base of the tail provided room for the enormous af-
terburner, so a final posterior appendix exposed the fodder to one
last digestive procedure.
The ankylosaur's rearward digestive system with its special af-
terburner surely was big enough to make up for its weak teeth.
Even quite tough vegetation could have been handled in large
volumes. My colleague and friend Ken Carpenter has evidence in-
dicating some species had gizzard stones as well. Could gastro-
chemical treatment have supplied the ankylosaurs with enough food
energy to be warm-blooded? Absolutely—at least the boundary
conditions from the dietary perspective must include this possibil-
ity. And at the very least the ankylosaurs too are rescued from the
category of soft-food-eating, low-energy semi-invalids.
Besides the major families of herbivorous dinosaurs dis-
cussed so far, there were a dozen smaller groups all outfitted with
plant-eating equipment of the sort already described for the major
families. Iguanodon was a relative of the duckbill. It won interna-
tional fame as the first dinosaur made known to science, when it
was dug from road-gravel quarries in Sussex, England, in 1822. The
iguanodont's adaptations were styled after the duckbill's—closely
packed chopping shredding teeth (although iguanodont's weren't
as complex as duckbill's). Dryosaurs must have been very selec-
tive eaters, using their narrow muzzles to crop carefully chosen
fodder. The fabrosaurs, the most primitive beaked dinosaurs, were
bipeds with small, loosely packed teeth like those of the much later
ankylosaurs.
Altogether, each dinosaur dynasty, from Early Jurassic to Late
Cretaceous, was equipped for a comprehensive attack upon fo-
liage, buds, bark, tubers, and fruit. Not one plant-eating dinosaur
has been found to subsist on aquatic plant mush. Every herbivo-
rous clan could have harvested land plants at rates and quantities
sufficient for high metabolism.
178 I THE HABITAT OF THE DINOSAURS
9
WHEN DINOSAURS
INVENTED FLOWERS
Darwin and his followers regarded the ecological drama as a
complex, choreographed struggle among competitors, pred-
ator, and prey. "Nature red in tooth and claw" expressed the vio-
lent aspect of natural selection, the killing and bloody rending of
flesh by predators' fangs, the maiming of sexual rivals during the
vicious combats between dominant males during the mating sea-
son. But Darwin was clever and observant; for all the violence of
nature, he knew that most evolutionary dramas were played to a
subtler script, the day-to-day interaction between the antelope and
the grass, the squirrel and the acorn. Plants and plant-eaters co-
evolved. And plants aren't the passive partners in the chain of ter-
restrial life. Hence today's Pop Ecology movement is quite wrong
in believing that plants are happy to fill their role as fodder for
herbivores in a harmonious and perfectly balanced ecosystem. A
birch tree doesn't feel cosmic fulfillment when a moose munches
its leaves; the tree species, in fact, evolves to fight the moose, to
keep the animal's munching lips away from vulnerable young leaves
and twigs. In the final analysis, the merciless hand of natural se-
lection will favor the birch genes that make the tree less and less
palatable to the moose in generation after generation. No plant
species could survive for long by offering itself as unprotected
fodder.
Plants evolve all sorts of devices to foil plant-eaters: They
WHEN DINOSAURS INVENTED FLOWERS I 179
The pygmy dinosaur, Nanosaurus, in the Late Jurassic underbrush.
Nanosaurus was a four-feet-long omnivore and a very primitive beaked
dinosaur. The understory plants are: a gingko (upper left), two cycadeoids
(on both sides, with diamond-sculpture trunks and big fronds), a fern (lower
left), and ground pine (foreground creepers).
poison them with deadly alkaloids; they keep them away with thorns
and spines; they render plant tissue unchewable by incorporating
rock-hard phytoliths into the plant cells or by toughening plant fi-
bers with cellulose; they avoid being eaten by producing new leaves
in early spring when plant-eating populations are low. Of course
the plant-eaters fight back. The evolution of herbivores leads
inexorably to better teeth for crushing the toughest leaves, to more
complex digestive systems where enzymes can detoxify plant poi-
180 | THE HABITAT OF THE DINOSAURS
sons, to taller shoulders and longer necks to reach higher into the
trees, or to lower heads and square muzzles perfect for cropping
ground-hugging leaves.
The warfare between plants and herbivores began on land 400
million years ago, when the first algae colonized the bare ground
during the Silurian Period and the herbivoro
us arthropods evolved
to follow them. Vertebrate plant-eaters on land appeared much
later, during the last epochs of the Coal Age, 270 million years
ago. Dinosaurs captured the herbivorous niches on land during the
Triassic, 200 million years ago, and subsequently maintained their
dominance through the entire Jurassic and Cretaceous. But how
did dinosaurs co-evolve in relation to the plants of their world?
Dinosaurs held the roles of large land herbivores for longer than
any other vertebrate group, so there must have been a rich history
of adaptive attack and counterattack between plant-eater and plant.
Moreover, herbivorous dinosaurs suffered several episodes of ex-
tinction and adaptive revolution that must also have been re-
flected in contemporary plant systems. And there was a momentous
development in the plants during the Mesozoic, for the Jurassic
and Cretaceous witnessed the single greatest event in the evolu-
tion of the modern system of plants—a turning point that must
have changed the life of every plant-munching dinosaur—the ap-
pearance of the flowering plants.
Today flowering plants, known collectively as angiosperms, are
by far the most numerous of land foilage, literally thousands of
species, including nearly all the plants that feed mankind and our
mammalian relatives. So numerous are angiosperms that to the av-
erage person, the term "plant" is synonymous with "flowering plant."
Oaks, birches, maples, and all the other broad-leafed trees are an-
giosperms, as are nearly all the berry-producing bushes and shrubs.
Palms, grasses, sedges, and dandelions also belong to the angio-
sperms, as do tulips and all the other species with showy flowers:
squash, beans, coconuts, lilies-of-the-valley, peaches, apples, or-
anges, rhubarb, tomatoes, cucumbers, onions, garlic, potatoes,
scallions, leeks, lettuce, spinach, broccoli, and thousands more. All
angiosperms are members of one natural group, descended from
a common ancestor that first appeared at the midpoint of the di-
nosaurs' reign.
The anatomy of the angiosperms is the key to their success.
WHEN DINOSAURS INVENTED FLOWERS | 181
They have distinctively complex reproductive organs—flower and
fruit—and most woody species additionally possess highly ad-
vanced conduction tubes in their roots, stems, and leaves, which
give them enormous advantages over other plants. Angiosperms
use their brightly petaled flowers to attract animal pollinators (in-
sects, bats, birds), and many use large fruit containing tough seeds
to attract animals as agents of dispersal. (Some modern angio-
sperms are wind-pollinated, but this is an evolutionary reversal. The
earliest flowering plants probably exploited animal vectors exclu-
sively.) Different flower shapes attract different species of insects,
bats, and birds, and thus each angiosperm creates the opportunity
of spreading its pollen efficiently without the wholesale waste in-
evitable in pollination by wind. The same is true for angiosperm
seeds and fruit, which are far more diverse and distinctive than
those of non-angiosperms.
So overwhelming is the advantage of the angiosperms today
that non-angiosperms are forced to play subordinate roles in the
flora of most areas. Today, the most conspicuous non-angiosperms
are conifers, cycads, ferns, ground pine, and horsetails. None of
these non-angiosperms produce flowers, and most rely upon the
wind to spread their spores, pollen, and seeds. Conifers—the
needle-leafed trees—are important in temperate forests, but they
are outnumbered by angiosperms ten to one on a worldwide av-
erage. Cycads with their spiny fronds are always a tiny minority in
every flora. Ferns, ground pine, and horsetails, very ancient relics
of Coal Age flora, make important contributions to the forest un-
dergrowth and to swampy herbiage. But these living Coal Age fossils
are outnumbered thirty to one by angiosperm species in nearly all
habitats.
How did flowering plants begin to win this unchallenged he-
gemony? Whatever the story, dinosaurs must have had a hand in
it because the earliest angiosperms sprouted up in a landscape
dominated by dinosaur plant-eaters. And they remained the major
outside factor for plants all through the first forty million years of
the angiosperms' evolution. But, for no apparent reason, modern
science has ignored the dinosaurs' role in plant evolution nearly
completely. Paleobotanists theorize about new insect groups which
might have co-evolved with the flowers in Late Cretaceous times.
Mammal paleontologists assert that Cretaceous mammals, no mat-
182 | THE HABITAT OF THE DINOSAURS
Iguanodon browses among the broadleaf saplings. Flowering plants began their
spectacular evolutionary career during the Early Cretaceous, when big-beaked
dinosaurs like Iguanodon fed close to the ground. Early angiosperm leaves
included some sassafraslike species (upper left), the broadly rounded
Proteaephyllum (lower left and in Iguanodon % mouth), and the oaklike
Vitiphyllum (right).
ter how tiny and unimportant, made a major impact on the evo-
lution of angiosperm fruits, nuts, and leaves. But hardly anyone
has argued for the interaction of Cretaceous dinosaurs with the
plants that fed them—an extraordinary oversight, considering the
dinosaurs were the only herbivores large enough to gobble an en-
tire flowering shrub in one gulp or strong enough to push an an-
giosperm tree so as to get at the tender young leaves at the top.
The consistent neglect of the dinosaurs' potential role in the
evolution of plants is one of the most pernicious examples of the
orthodoxy that relegates the dinosaurs to what amounts to an evo-
WHEN DINOSAURS INVENTED FLOWERS I 183
lutionary sideshow, a menagerie of irrelevant dead ends that can
be ignored so far as any large implications are concerned. Today,
large herbivores can change the structure of the flora overnight.
Rhinos and elephants can level acacia groves and rapidly crop down
thickets, converting dense African bushland into open woodland.
In the early nineteenth century, the American buffalo kept push-
ing back the boundary between prairie and forest by its intensive
grazing on seedlings. Surely four-ton nodosaurs and three-ton
iguanodonts did the same in the Early Cretaceous system.
Another bias also works against herbivorous dinosaurs, how-
ever. Paleobotanists are a bit chauvinistic about their objects of
study. They tend to regard plants as the movers and shakers in
evolution, and the plant-eaters are consigned to the role of reac-
tors and followers. As one paleobotanist expressed it, "The sun
gives energy to plants, and plants give energy to the animals.
Therefore, the plants evolve and the animals must co-evolve." Stated
thus, the assertion is understandable, but it's misleading. Co-evo-
lution works both ways. When plant-eating dinosaurs evolved more
effective teeth or fermenting chambers, the plant
species had to
adjust to the new weaponry or die. Whichever evolved faster, plant
or animal, had the evolutionary initiative. And plant-eating dino-
saurs evolved fast, faster than the plants. On average, a species of
dinosaur endured two or three million years before becoming ex-
tinct and being replaced by a new species. That's a brisk rate of
evolutionary turnover, as fast as the mammals'. Such rapid re-
placement of old adaptive models by new ones guaranteed that the
dinosaur plant-eaters were always coming up with novel ways to
bite, chew, ferment, and digest plant tissue. Mesozoic plants, on
the other hand, usually evolved more slowly—the average species
of plant lasted eight million years before being replaced by a new
one. Since the turnover wasn't as fast, the plants must have been
lagging behind the dinosaurs in the evolutionary race.
Herbivorous dinosaurs in fact were the fastest-evolving part
of the entire Mesozoic land ecosystem, even faster at adaptive re-
modeling than their meat-eating relatives. Tyrannosaurus rex, the
fifty-foot-long Cretaceous killer with seven-inch teeth, was really
just a sophisticated variation on the basic predator plan first evolved
a hundred million years earlier in the Late Triassic. Bone by bone,
Tyrannosaurus rex was fundamentally little different from its an-
184 I THE HABITAT OF THE DINOSAURS
cient Triassic ancestors. But the Cretaceous plant-eaters—three-
horned Triceratops, club-tailed Ankylosaurus, broad-beaked Edmon-
tosaurus—carried skull and jaw developments totally unknown in
the Triassic.
To follow the pattern of co-evolution between dinosaurs and
plants, the major turning points in the development of each must
be defined, then laid side by side. Among the herbivorous dino-
saurs, three grand periods of development are clearly marked:
I. The Age of Anchisaurs. The Late Triassic and Earliest Juras-
sic, when the long-necked anchisaurs ruled. Anchisaurs were
primitive, crude plant-eaters by Cretaceous standards. They had
simple, iguanalike teeth, suitable for soft leaves only, and their
digestive system wasn't much expanded.
II. The Age of the High Feeders (stegosaurs and brontosaurs).
The Mid and Late Jurassic, when the spike-tailed stegosaurs joined
Robert T Bakker Page 19