floodplain mud preserves mostly landlubbers. What is needed, then,
beyond the single Cam Bench Camarasaurus, to solve the mystery
of the brontosaur's habitat is a broad statistical survey. Thanks to
a National Geographic research grant, a group of brontosauro-
THE CASE OF THE BRONTOSAURUS: FINDING THE BODY I 115
philes called the "Morrison Dinosaur Habit Research Group" was
able to make just this type of survey between 1974 and 1977.
A study trench was dug up through the whole three-hundred-
foot thickness of the Morrison Formation at Como. It laid bare
cycle after cycle of life, death, burial, and new life. Twenty differ-
ent kunkar layers were exposed, each marking a time when a
floodplain was dry and green and its vegetation nourished dino-
saur life. And just above each kunkar layer were zones of fossils
—chewed dinosaurs—whose bodies had been written into rock his-
tory by entombing layers of mud. When the statistics were tabu-
lated, eighty percent of the brontosaur graves were in floodplains,
twenty percent in river channels and zero percent in lakes or
swamps.
But the quarries at Sheep Creek, Wyoming, twenty miles north
of Como, posed a special mystery. Here was a big quarry full of
brontosaurs—and their carcasses had been entombed in lake-bot-
tom limestone. Had lake-dwelling brontosaurs been found at last?
Did the Sheep Creek skeletons represent bottom-walking behe-
moths that fed on soft lake plants just as brontosaur orthodoxy
had preached for eighty years? If the Sheep Creek limestone was
deposited in a deep lake, then perhaps the brontosaurs found here
were the classic dwellers in aquatic habitats.
A careful investigation of the quarry made it clear that some-
thing was wrong with the deep-lake theory. As a carcass sleuth looks
for clues, he or she must be alert for negative evidence; some-
times what's missing reveals more than what is present. And neg-
ative clues were everywhere at Sheep Creek. No fish bones or
crocodile bones and almost no turtle remains (only one fragment
of shell) were ever found in the Sheep Creek limestone. What sort
of lake had no fish or crocodiles or aquatic turtles? Nearly all
tropical lakes today are quite full of these swimming creatures. Snail
shells were found, but only of the type usually present in ponds
and along lake margins.
More perplexing clues turned up. Kay Behrensmeyer, among
the best young American taphonomists, found giant dinosaur
footprints in the same limestone which contained the dinosaur
bones. Bottom-walkers can make shallow prints in the mud under
deep water. But these prints were far too deep to have been made
by a brontosaur buoyed by twelve feet of lake.
116 | THE HABITAT OF THE DINOSAURS
Finally, a key piece of the puzzle fell into place. "Fossil sun-
light," in the form of mud cracks in the lake bottom, turned up.
When mudflats are exposed to air, the mud surface dries and con-
tracts, cracking itself into a mosaic of hexagons separated by fis-
sures. In a sunny, dry climate, mud cracks can grow to depths of
a foot or more quite quickly. And such cracks can fossilize when
a subsequent flood washes a layer of sand over the cracked mud-
flat, filling the fissures with sediment. Usually the soil filling the
fissures has a different texture from that of the mudflat. So when
a fossil mudflat and its crack-filling are exposed by erosion, the
ancient dried surface faithfully preserves the record of sunrays
millions of years old.
Mud cracks in the lake-bottom limestone proved that the lake
had dried up repeatedly. Such sun cracks were found on several
layers piled on top of one another on the ancient lake bottom. If
the Sheep Creek dinosaurs had died in a shallow lake, then the
strange negative clues could be easily explained. Shallow lakes are
subject to cycles of drying up and wetness; some lake beds in to-
day's tropical Africa are dry most of the time and fill up only dur-
ing exceptional floods. Small snails can live in such shallow water,
but bigger swimming creatures—fish, turtles, and crocodiles—ob-
viously cannot. The best explanation for the peculiarities of the
of swamp-living brontosaurs. These brontosaurs probably did die
on a lake bottom, or at least near it. But there probably was not
enough water in the lake to float a small crocodile, let alone a multi-
ton dinosaur.
The ultimate irony at Sheep Creek is that the dinosaurs may
have died there during a drought. When dead bodies lie on dry
land for awhile, the air and sun desiccate the muscles and back
ligaments, contorting the entire body so that the neck and tail are
twisted up above the level of the back. Did drought kill the bron-
tosaurs? There was strong evidence for dry seasons during the
brontosaur's heyday in the late Jurassic. Beds of lime pellets show
up in dozens of layers, and each kunkar zone recorded a time of
repeating dry seasons. But the contorted state of the brontosaur
bodies provided the strongest proof of terrible drought. At Sheep
Creek, the eighty-foot body of a brontosaur was twisted precisely
in the manner of a drought victim. And at Dinosaur National
THE CASE OF THE BRONTOSAURUS: FINDING THE BODY | 117
Monument in Utah, a four-hundred-foot-wide stream bed pre-
serves dozens of gigantic dinosaur bodies, all twisted with their huge
necks and tails over their backs. Similar scenes of Jurassic death
by drying are repeated in quarry after quarry.
Ordinarily, carcasses are pulled apart by scavengers right after
death. If the weather is mild, lions, hyenas, and jackals can reduce
a dead elephant to a scattered mass of disjointed bones in a few
days. But drought kills animals faster than the scavengers can dis-
member them, and severe drought kills the scavengers too. So the
landscape becomes full of bodies drying up under the sun. Scores
of brontosaur bodies found in the Morrison beds show the telltale
signs of mummification under the merciless sun of Jurassic droughts.
Our scenario of what occurred at Sheep Creek contains the
script for a Jurassic tragedy. Around the shores of a drying lake
bed gather the beleaguered giants— Diplodocus, Brontosaurus, Steg-
osaurus. With their huge elephantine feet they dig into the mud,
trying to reach the water table fast receding under the desiccating
Mesozoic sun. For a few weeks the giants survive, drinking from
the muddy water which seeps into the deep holes excavated by
their feet. Smaller dinosaurs sneak in to drink when the giants are
unaware, though the biggest brontosaurs angrily defend their
dwindling water stores. Finally even the strongest cannot survive.
Twenty-ton bodies collapse on the lake shore and twist into sun-
dried mummies. After six months or a year or two, the monsoon
rains return. The level of the lake rises, spreading a soft blanket
of limy mud over the sun-dried bodies lying on the parched clay.
The final box score tabulated for the survey of brontosaurs
was emphatically in favor of land habits. Few brontosaurs were
buried in deep lakes. Many died and became entombed on flood-
plains where the water creatures—crocs and turtles—were rare or
absent. Altogether, the brontosaurs showed the same burial pat-
tern Kay Behrensmeyer has observed for land-living elephants in
East African sediments.
We then reconstructed the overall environment from the
patchwork of different individual habitats found throughout the
landscape during Morrison times. This broader level of sleuthing
yielded a picture of the Jurassic world in the Western United States.
It consisted of a system of broad, flat floodplains, small rivers,
shallow ponds, and occasionally deep lakes, all subjected to cycles
of killing droughts.
118 | THE HABITAT OF THE DINOSAURS
After the results of our carcass-sleuthing in the Morrison, a
nagging question remained. Why did the brontosaurs die out in
Wyoming and Colorado at the end of the Jurassic Period?
After achieving extraordinary success right up into the last
Late Cretaceous brontosaurs avoided swampy forests. The Alberta delta was
wet year-round most years, and brontosaurs weren't there. But in North
Horn, Utah, there was a distinct dry season (producing kunkar) and the
THE CASE OF THE BRONTOSAURUS: FINDING THE BODY
119
zones of the Jurassic, the brontosaur clan declined suddenly in
Wyoming and Colorado before the waves of new dinosaur fami-
lies flooding the land ecosystems at the beginning of the Creta-
ceous. These new dinosaurs of the Cretaceous were all members
of the beaked Dinosauria. And the entire Cretaceous Period re-
cords the proliferation of beaked dinosaurs into several rich fam-
ilies of duckbill dinosaurs, armored dinosaurs, and horned dinosaurs.
This transition from the Jurassic to the Cretaceous marks the most
profound shake-up in the history of dinosaurian families.
Why did brontosaurs lose their ecological preeminence in these
areas? According to most books on dinosaurs written for children,
the swamp-loving brontosaurs would have died out as their marshy
haunts drained away. Our comprehensive survey of brontosaur
quarries has already shown that this view simply won't hold—Ju-
rassic brontosaurs were living and breeding for millions of years
in habitats with a distinct dry season.
There is, however, another good explanation for the absence
of the brontosaurs from the areas they had formerly dominated,
an explanation that takes dinosaur orthodoxy and stands it on
its head.
To understand this disappearance of the brontosaurs prop-
erly, we must turn to the great deltas of the Cretaceous. Deltas
are formed where rivers meet the sea. Where the modern Missis-
sippi flows into the Gulf of Mexico, for example, the mud-laden
river water dumps millions of tons of sediment every year along
the boundary between land and ocean. This influx of sediment is
building a huge mud platform out into the Gulf. In Late Creta-
ceous times, a series of short rivers flowed eastward from the ris-
ing young mass of the Rocky Mountains into a broad and shallow
sea that covered most of what is now the High Plains country of
eastern Alberta, Montana, and Wyoming. Together, these Creta-
ceous rivers built a continuous sequence of overlapping deltas from
Canada south to New Mexico, and these deltas are full of dino-
saur skeletons.
These Cretaceous deltas are among the best-studied dinosaur
habitats of the entire Mesozoic, because compelling economic in-
terests drive geological exploration—the deltaic sands are often full
of oil and the deltaic swamp deposits are full of coal. Thanks to
the oil and coal companies, which have poured millions into re-
120 I THE HABITAT OF THE DINOSAURS
search, and to American and Canadian museums, which have con-
sequently excavated hundreds of dinosaurs, the climate and
landscape of the Cretaceous deltas can be reconstructed in minute
detail. Conditions had clearly changed from Jurassic days. Gone
were the dry meadows and kunkar-layered soils. In their place stood
stagnant bayous, estuaries, and cypress swamps like those of pres-
ent-day Louisiana. Beneath these broad bodies of delta water, or-
ganic residue from innumerable rotting leaves and branches was
continuously pressed into a compact, carbon-rich coal.
These deltas began yielding dinosaurs in the 1880s. The rock
layers they contained were named the Laramie Beds after the Wy-
oming frontier town. Now, if the orthodox story of brontosaur
habits is to be believed, then the Laramie Deltas should have been
prime brontosaur country. But the brontosaurs aren't there. Di-
nosaurs in profusion are found in the Laramie Deltas—beautifully
preserved skeletons, with every joint in place, of duckbill dino-
saurs, horned dinosaurs, armored dinosaurs. But after a century of
thorough exploration, not one brontosaur has turned up.
Yet brontosaurs did still exist during this time. Late Creta-
ceous beds in Brazil, Argentina, India, Mongolia, and even in close-
by New Mexico have yielded dinosaurs. Why then did these
latter-day brontosaurs avoid the Laramie Deltas?
Perhaps a consummately heterodox suggestion answers that
question: Maybe the brontosaurs did not need soggy terrain, maybe
they positively hated it. Some of today's large animals—zebra, wil-
debeest, and lions, for example—dislike swamps intensely. Bron-
tosaurs may have disliked the mushy soil so much that they avoided
the swampy deltas entirely.
This idea could be tested in the quarries of the North Horn
Mountains of Utah, the northernmost locales that contain Late
Cretaceous brontosaurs. If the North Horn quarries contain evi-
dence for dry, well-drained floodplains—the type of habitat miss-
ing further north in the area of the Laramie Deltas—then a strong
case for hydrophobic dinosaurs can be made, and their decline in
Wyoming and Colorado in Cretaceous times consequently ex-
plained.
Alamosaurus, "lizard of the Alamo," is the name given to the
Cretaceous brontosaur found in Utah. "Alamo" in this case refers
to the Ojo Alamo Mountains of New Mexico where the beast was
THE CASE OF THE BRONTOSAURUS: FINDING THE BODY I 121
The Alamo brontosaur in its dry Utah home. Two Alamosaurus (at left) watch
as a meat-eating Albertosaurus tries to attack the spiny-frilled Styracosaurus (at right). A trombone-crested duckbill (Parasaurolophus) flees the scene. During
these Late Cretaceous times, the brontosaur clan avoided the humid habitats
of the northern deltas in Wyoming and Montana and Alberta, but farther
south, where summers were dry and hot, Alamosaurus reigned supreme as the
biggest plant-eater.
first found in 1922. When that first Alamosaurus was found, it jolted
American paleontology; until then, no one had found a single scrap
of Late Cretaceous brontosaur in the United States. And it had
been assumed that all the North American brontosaurs had died
out long before Late Cretaceous times.
The best specimen of Alamosaurus was excavated from a
beautiful cliff face within the North Horn Mountains of Utah. Di-
nosaurs from the North Horn constitute an intriguing mix. Sci-
entists from the Smithsonian Institution have disinterred horned
dinosaurs, duckbills, and flesh-eating tyrannosaurs—all three groups
that dominate in the Cretaceous deltas of Wyoming-Alberta. But
they have also discovered several gigantic brontosaurs, all belong-
ing to Alamosaurus. And the North Horn quarry did not at all re-
semble a typical Cretaceous delta. Instead, it looked precisely like
a Jurassic quarry from Como. A walk up the cliff face yielded a
count of seven distinct layers of lime pellets. So the North Horn
habitat in Late Cretaceous times was much less soggy, on average,
than the contemporaneous locales on the deltas in Wyoming. Like
its Jurassic forebears, therefore, Alamosaurus lived and died in a
landscape of dry, well-drained floodplains.
The ultimate in heterodox thinking seems justified. And
brontosaur orthodoxy had it completely incorrect. Brontosaurs
didn't require deep swamps to buoy their bulk; they didn't even
like to be near swamps. Brontosaurus and its kin of the Jurassic
Age favored truly terrestrial haunts with dry soils. And when great
swamps did spread across vast areas of the Cretaceous world, as in
Wyoming and Colorado, the brontosaur clans simply eschewed this
soggy terrain and moved their evolutionary centers elsewhere, to
locales where the brontosaurs could feel the reassuring texture of
dry floodplains beneath their feet.
124 | THE HABITAT OF THE DINOSAURS
6
GIZZARD STONES AND
BRONTOSAUR MENUS
Seen from a distance, a live Brontosaurus would appear not to
have any head at all. Both neck and tail would just seem to
taper gradually to a point both fore and aft. Up close the head
would appear, of course—about the size of an average horse's. Less
than two feet of brontosaur head to go with seventy feet of neck,
body, and tail. A two-foot horse's head, with a mouthful of big
molar teeth, can feed an eight-hundred-pound horse body. A two-