as a gazelle's or an ostrich's, and most large dinosaurs had a
shank + ankle -5- thigh index of 1 or perhaps a little higher. There-
fore, it's been concluded that short-shanked dinosaurs were lim-
ited to low-gear locomotion. Triceratops had a quite stubby ankle
index and was therefore allegedly incapable of any fast movement
at all. But all horned dinosaurs had shanks that were actually much,
much longer than a rhino of the same weight. These dinosaurs only
seem to have relatively short ankles and shanks because the thigh
is much larger than a rhino's.
Triceratops was indeed shorter in the shank than a modern rhino
is, but that doesn't prove Triceratops couldn't run as fast or faster.
Triceratops had tremendously strong limb bones, and that strength
must have evolved to withstand great forces. The unbelievers who
scoff at the notion of a galloping Triceratops will have to explain
why dinosaurs evolved such strong, thickly shafted limbs if they
were going to do no exercise more strenuous than a shuffle through
the swamps.
A third argument has occasionally been advanced against the
notion of fast speeds in quadrupedal dinosaurs. Mammals today
use their shoulder blades as arm extenders, swinging each long blade
fore and aft with every stride. Dinosaurs supposedly possessed rigid
shoulder blades that had to remain in place against the ribcage. If
THE TEUTONIC DIPLODOCUS: A LESSON IN GAIT AND CARRIAGE I 219
this theory of the stiff shoulder is correct, Triceratops would have
had considerable trouble locomoting because its forelimbs were
much shorter than its hind limbs. If both fore- and hind limbs were
working at full stride, the rear end would move faster than the
front end and the five-ton monster would have the option either
of turning circles or of flipping over altogether—a most maladap-
tive model of locomotion!
Working on my undergraduate thesis, I had toyed with the
hypothesis that the dinosaurs' shoulder blades might have swung
across the ribcage, but I was unable to build a reliable support for
220 | DEFENSE, LOCOMOTION, AND THE CASE FOR WARM-BLOODED DINOSAURS
such heterodox mechanics. Later, at graduate school, I met a fel-
low student, Jane Petersen, who had just completed a thesis about
the shoulders of chameleons. She proved that chameleons could
swing their long shoulder blades fore and aft more freely than other
lizards, because the chameleon's blade was not locked onto the chest
by a bulky collarbone. This impressed me because I had already
noticed that chameleons were the only lizards that looked like di-
nosaurs in the shoulders. Both dinosaurs and chameleons have very
long, slender shoulder bones that work completely free of re-
straint from the collarbone, which anchored the shoulder blades
Triceratops—stronger than a
bull elephant. A five-ton
African bull elephant has
legs that are much thinner,
and much weaker, than
were those of a five-ton
horned dinosaur. And so
the dinosaur was able to
withstand much greater
stresses during running.
THE TEUTONIC DIPLODOCUS: A LESSON IN GAIT AND CARRIAGE | 221
in all most primitive reptiles. Chameleons evolved from some
"normal" lizard ancestor that possessed a thick, stiff collarbone
which held the shoulder blade in place. But chameleons shed that
collarbone along their evolutionary path to provide themselves with
more participation from their shoulders in the strokes of their fore-
limbs. Dinosaur evolution must have been the same—dinosaurs
experienced the same reduction of the collarbone and must have
developed a similar free-swinging shoulder. And the big quadru-
pedal dinosaurs evolved the longest shoulder blades of any verte-
brate, past or present. As its yard-long shoulder swung alongside
The horned dinosaurs—longer, faster,
stronger legs than rhinos. A two-ton
centrosaur had legs that were thicker, longer,
and more powerfully muscled than those of a
two-ton black rhino.
222 | DEFENSE, LOCOMOTION, AND THE CASE FOR WARM-BLOODED DINOSAURS
Triceratops % ribcage, the extra length added to its forelimb must
have given the animal a grand propulsive boost. Both fore- and
hind limbs were consistently designed for fast, maneuverable
movement.
Such outlandish heterodoxy proves doubly sweet when sup-
ported by independent confirmation. Fossil footprints are the only
direct evidence left by locomoting dinosaurs, so a set of tracks left
by some speeding Tyrannosaurus would provide dramatic confir-
Swinging shoulder blades—a
modern horse, a modern
chameleon, and the three-
ton horned dinosaur
Centrosaurus
BELOW: Collarbone
prevented shoulder-blade
swinging. Primitive dinosaur
ancestors—like this Early
Triassic Chasmatosaurus—
couldn't use their shoulder
blades for long fore and aft
swings because the
collarbone held the
shoulder blade tightly
against the sides of the
chest and the breastbone.
THE TEUTONIC DIPLODOCUS: A LESSON IN GAIT AND CARRIAGE | 223
Five tons of Triceratops'
at full gallop
mation. The English biologist McNeil Alexander has worked out
a clever formula for computing speed from trackways: all that is
necessary is the length of stride and the toe-to-hip measurement.
When first applied to some samples of dinosaur prints, the for-
mula yielded low speeds—two to four miles per hour. Some com-
mentators immediately jumped to the conclusion that this
conclusively proved the theory of slow dinosaurs. That is non-
sense. Most fossil trackways represent slow cruising speeds, not
top speed, because all species spend most of their time moving
along in an unhurried fashion. Bursts of maximum velocity erupt
only rarely, when a predator charges or a plant-eater scampers for
its life. Most tracks left by gazelles and rhinos today are made at
a slow speed when these animals are feeding or going to or from
water holes. Rhinos don't live their entire lives at thirty-five miles
per hour; a trackway that caught one of these rare moments when
the rhino was galloping full tilt would be a most extraordinary find.
Trackways from big quadrupedal dinosaurs are rare—there exist
only four sites with good brontosaur tracks—so the sample is far
too poor to argue any case about top speed.
224 | DEFENSE, LOCOMOTION, AND THE CASE FOR WARM-BLOODED DINOSAURS
Bipedal dinosaurs are represented by more tracks—hundreds
altogether—so a few tracks might conceivably capture a moment
of high speed. And a few two-legged trackways do provide such
proof. Several medium-sized, fifty-pound to half-a-ton bipedal
predators have left long-striding tracks which compute to speeds
of twenty, thirty, or even forty miles per hour.
Narrow tracks,
swinging shoulders, stout-shafted limbs that
bounced at every stroke—all these bits of modern evidence agree
with the lively restorations drawn for Marsh and Cope way back
in the 1890s. Cope had a painting made of Dryptosaurus, showing
a pair of the giant meat-eaters excavated from the phosphate mines
of New Jersey. Cope's dryptosaurs were portrayed in violent lo-
comotor exercise. One was flung on its back, hind legs lashing out
in claw-tipped defensive strokes; the other was painted in mid-leap,
its great hind legs having propelled its body far above the ground.
A good painting, far more faithful to the real structure of dinosaur
locomotion than the shuffling reconstructions popular in most or-
thodox textbooks today. Speed and vigor were the way of the
dinosaurs, multi-ton monsters able and ready to break into a fast-
paced charge whenever necessary. The Mesozoic was life in the
behemoth fast lane.
THE TEUTONIC DIPLODOCUS: A LESSON IN GAIT AND CARRIAGE | 225
11
MESOZOIC ARMS RACE
Humans are one of the least armored products of evolution.
Perhaps our own defenseless hide renders the apparently bi-
zarre armor plate sported by three great clans of beaked dino-
saurs—the Stegosauria, the Ankylosauria, and the horned
dinosaurs—especially fascinating. The story of these armored di-
nosaurs is a drama out of the Mesozoic arms race, the co-evolu-
tionary link between ever deadlier meat-eaters and ever more
formidably protected prey.
Stegosaur tails were without question one of the most dan-
gerous weapons ever evolved by a plant-eating animal. At the ex-
treme end of the stegosaur's long tail sprouted a fearsome war club,
composed of four or eight sharply pointed spokes between two
and three feet long. Extra-thick connective tissue in the skin an-
chored the bases of these bony spikes so that the points extended
outward, and upward, and backward. And pits left by blood ves-
sels on these spikes show that they were sheathed by a very thick
horn cover in life, much like the outer sheath of longhorn cattle
today. Horn constituted the ideal sheathing material for such sharply
pointed weapons because it is more flexible and less brittle than
bone and thus can be honed to a much sharper point.
To drive all those pointed tail spikes deep into the body of
its adversaries, Stegosaurus required a tail of great power and flex-
ibility, and both qualities were in abundant supply. To acquire
226 I DEFENSE, LOCOMOTION, AND THE CASE FOR WARM-BLOODED DINOSAURS
flexibility in the tail, the stegosaurs' evolution had to dispose of a
major feature of their ancestry, the system of stiff tendons. Most
beaked dinosaurs featured a latticework of bony tendons running
down either side of their backbones from torso to tail. And all the
earliest, most primitive beaked dinosaurs possessed such equip-
ment. As has already been discussed, this latticework—best seen
in duckbills and horned dinosaurs—would have provided an ad-
vantage for supporting the body weight without muscular effort.
But such bony tendons would have stiffened the stegosaur's tail
The big-plate stegosaur Diracodon
battles a Ceratosaurus
MESOZOIC ARMS RACE | 227
too much for easy swinging. Evolution therefore eliminated the
system of tendons and the stegosaurs were the only beaked dino-
saurs to do away with bony tendons entirely. But merely elimi-
nating bony tendons wouldn't have been enough to render the
stegosaur's tail optimally dangerous. Since the spikes stood at the
tail's extreme tip, the bones of the tail had to be both strong and
flexible all the way to the end. In most dinosaurs the tail joints
grew progressively stiffer toward the end, but not so in stego-
saurs. The joints between the successive segments of the tail gave
its entire length from rump to tip enough suppleness to flex in a
graceful S-shaped curve, and the vertebrae were much stronger than
usual near the end.
To achieve the muscular strength necessary to swing its club,
the stegosaur evolved enlarged shelves of bone for anchoring its
muscles (similar shelves had evolved in the big-tailed brontosaurs,
such as Diplodocus). A twenty-foot-long stegosaur would have had
more strength in its tail muscles than a large modern elephant has
in one of its hind legs. And when the mighty tail muscles con-
tracted, the stegosaur's caudal club swung with irresistible authority.
The eight-spiked Stegosaurus ungulatus
228 | DEFENSE, LOCOMOTION, AND THE CASE FOR WARM-BLOODED DINOSAURS
Stegosaurs had need of such a war club because they faced
predators nearly as large as elephants. Allosaurus and Ceratosaurus,
the two most common Late Jurassic flesh-eaters, both grew to
lengths of thirty feet and more and would have weighed between
one and two tons. Even larger was Epanterias (possibly a very large
reached four tons, six times heavier than a large lion. If such huge
flesh-eaters attacked in groups (a tactic widely believed possible),
only the most heavily armed plant-eaters could have survived.
Imagine the potential of the stegosaur's tail spikes in such a con-
frontation. If the three- to four-foot-long spikes were driven full
force into the chest or belly of even the largest predator, the re-
sult would have been devastating. Not even Epanterias would have
survived a direct hit.
But to fight well, Stegosaurus would have had to maneuver
quickly, pivoting about to keep its tail club facing the attacker. Al-
losaurus and Ceratosaurus were long-legged and nimble-footed, and
could have danced around the stegosaur in order to lunge in for
bites at the vulnerable neck or shoulders. How could evolution
equip the stegosaur with the necessary maneuverability to employ
its tail club to best advantage? The solution was found in its unique
body proportions and its short but thickly muscled forelegs.
Stegosaurs appear ungainly at first sight—their hind leg was much
longer than the fore, the hips much taller than the shoulder. The
combination of a heavy rump and tail with short forelimbs placed
the point of balance of the stegosaur's body just forward of the
hips, so that the beast could easily have pivoted around by push-
ing sideways with its forepaw.
The muscles employed to push sideways with the arms are
known as the deltoids. In most dinosaurs the deltoids were mod-
erately strong but not unusually so. But stegosaurs possessed prize-
winning deltoids, and the site where they attached to the upper
arms (humerus) was gigantic, larger than in any other vertebrate.
Obviously then, when threatened by a predator, the stegosaur
shifted its weight back onto its hind feet, then pushed with its fore-
feet, to rotate right or left in order to keep its deadly tail facing
the foe. Its huge deltoids provided sufficient power for pivoting
its entire body mass with ease.
Stegosau
rus is, however, best known not for its war club, but
MESOZOIC ARMS RACE I 229
Stegosaur muscles for quick turns. The deltoid muscle group had a huge
sideways-facing crest on the upper arm (humerus) so that stegosaurs could
push their bodies to one side or another. Powerful triceps muscles running
from shoulder blade to elbow gave the stegosaur a forward-lunge capacity.
for the spectacular triangles of bone that rose up to four feet above
its backbone. Though tall and broad, they were thin in section and,
like the tail spikes, were sheathed in life by an outer layer of horn.
Roughened zones along the bases reveal that these bony plates were
embedded in the skin along the top of the spine. Most restora-
tions show these plates sticking straight up from the back. But that
is a most puzzling orientation for them. What could have been the
bioengineering purpose of these strange triangles? Some paleon-
230 | DEFENSE, LOCOMOTION, AND THE CASE FOR WARM-BLOODED DINOSAURS
How stegosaurs flapped their plates. Stegosaur ancestors had bony armor
plates shaped like those of gators—the plate base was very wide and firmly
embedded in the outer layer of tight skin. But during stegosaur evolution the
plate base became very narrow and a sheet of skin muscle attached to the
sides of the plate to swing it from side to side.
tologists have suggested that if the stegosaur's plates stood up ver-
tically, they might have offered some defense against bites directed
at the backbone. But the stegosaur's spinal cord was already well
protected without the plates. It lay deep beneath the very tall ver-
tebral spines and the ligaments, which together constituted a very
tough hump over the torso and hips, much like the ridge on a
modern razorback hog. Any Allosaurus unwise enough to bite into
that ridge would have broken off its teeth without inflicting sig-
MESOZOIC ARMS RACE I 231
nificant damage. Moreover, the largest plates were located over the
hips and base of the tail, where the spinal cord was already best
protected by vertebral spines. The stegosaur's spinal cord was so
well armored by the backbone that the triangular plates really
wouldn't have added extra protection. And it appears like a re-