marine propulsion. And its needle-sharp claws would have been
perfect for snaring slippery aquatic prey. Maybe Archaeopteryx
sometimes hunted like present-day fishbats, occasionally snagging
fish with its hind claws as it swoops and glides over the surface of
the sea.
It must be said, restoring Archaeopteryx to its proper place in
the dinosaur's family tree has been a great boost to the morale of
dinosaurophiles. No open-minded observer of the fossil se-
quence, from Coal Age reptiles with stubby legs to the birdlike
dinosaurs of the Jurassic, can be other than convinced that our
present glorious array of feathered creatures is truly the direct de-
scendant of those primitive land creatures via the intermediary
agency of the dinosaurs. There are over eight thousand species of
birds alive in today's ecosystems, and each one, from the hum-
mingbird to the ostrich, is incontrovertible evidence that the
bloodlines of the dinosaurs are still full of evolutionary vigor.
The story of Archaeopteryx is a boon to dinosaur-lovers in an-
other way as well. According to the orthodox theory, remember,
dinosaurs didn't have enough metabolic energy to walk fast, let
alone fly. But both pterodactyls and birds had to evolve high-pres-
sure hearts and lungs before flight could be achieved. Pterodactyls
most probably were the descendants of very primitive dinosaurs,
of the bunnycroc variety, while birds were surely products of the
advanced dinosaurs. If both branches possessed a high-pressure,
ARCHAEOPTERYX PATERNITY SUIT: THE DINOSAUR-BIRD CONNECTION
321
hot-blooded metabolism, then it's not impossible to suppose that
the entire stock of primitive dinosaurs was already equipped for
high metabolism before either aerialist tribe evolved. In other
words, it's quite possible that flying dragons and birds inherited
their high-capacity hearts and lungs from their dinosaur forebears
and that powered flight was simply one application by evolution
of the fundamental bioenergy of the dinosaurs.
322 | DEFENSE, LOCOMOTION, AND THE CASE FOR WARM-BLOODED DINOSAURS
PART 4
THE WARM-BLOODED
METRONOME
OF EVOLimON
15
SEX AND INTIMIDATION:
THE BODY LANGUAGE OF
DINOSAURS
Ever since the first Mesozoic fossils came to light, there have
been features of them that appear to defy explanation, at least
in terms of the usually considered aspects of the Natural Econ-
omy—eating, drinking, preying, avoiding predators. As each new
species was excavated, the list of prehistoric anomalies grew: sail-
backed reptiles from the Coal Age, horned amphibians from the
ancient red beds, battering-ram skulls on the protomammals, ba-
roque crests on the heads of duckbill dinosaurs. American paleon-
tologists traditionally favored a strictly utilitarian interpretation of
these things; bones should be shaped to perform a useful function
for procurement of food or defense. Bones of nonutilitarian shape
were therefore puzzling in the extreme. Faced with a bewildering
variety of crests and cranial ornamentations, the older generation
of American paleontologists sometimes advocated a moralistically
motivated theory of racial decadence: As an evolutionary family
approached its time of extinction, its species would indulge in
nonadaptive decoration. Like biological ancient Romans, they had
supposedly lost control of their adaptive sense and hastened to their
doom amid orgies of useless ornamentation.
Until the 1970s, few American scientists referred to sex when
they analyzed dinosaur skeletons. But evolution is full of sex. And
natural selection favors structures that produce results in winning
or enticing mates and discouraging rivals. The beauty of nature is
SEX AND INTIMIDATION: THE BODY LANGUAGE OF DINOSAURS I 325
The great finback Dimetrodon attacks
the amphibian Eryops.
not spoiled by the great influence wielded by sex and intimida-
tion. Nor does it lessen the fascination of fossils to suspect that
much of the most extraordinary bony paraphernalia may have served
as enticements to prospective mates.
The early chapter of the sexual epic can be read back in the
steamy days of the Coal Age, long before there were any dino-
saurs. The primitive vertebrates with legs of that period would be
classed as amphibians in the reproductive sense of that term, for
they laid eggs, frog-fashion, in water. It is certain they reproduced
in water, because aquatic hatchlings are common fossils in the dark,
carbon-rich shales laid down in the lakes of the Coal Age. Often
the skin of these ancient larvae is outlined in the stone where the
slow decay distilled the living body tissue into an oily stain sur-
rounding the skeleton. These larval amphibians are fossils of
unexcelled loveliness. Dark organic outlines mark out each limb
and, behind the head, the long branched filaments of their gills.
326 | THE WARM-BLOODED METRONOME OF EVOLUTION
Gills just like these, pulsing with oxygen-rich blood, can be found
in the throats of modern salamander larvae. Holding a live sala-
mander in a handful of pond water is like looking back into a past
300 million years old, back to a time when the evolutionary tree
of land vertebrates had just taken root.
For the first fifty million years of life on land, all of the ver-
tebrates with legs were amphibians of one tribe or another. How
did they court each other? Since they reproduced in water, their
pre-nuptial displays must have taken place in ponds and quiet
backwaters or along the banks of ancient waterways. Living am-
phibians feature some of the richest sonic symphonies in today's
ecosystem—the chorus of mating frogs. But another amphibian
family, the salamanders, far more primitive than frogs, is nearly
mute. Some salamanders (the newts) substitute dance for song. The
male newt waves his tall, bright red tail in a kind of underwater
flutter-dance as he minces before his prospective lady love. The
fossil records from the earliest Amphibia do turn up some eel-like
tails that could have been used in this fashion. But what about
sound? When did amphibians evolve that marvelous capacity for
serenade so characteristic of modern frogdom?
The early fishes did not hear airborne sounds, and their ears
were used mostly to maintain body balance. Ears for hearing on
land require a taut membrane in the skull to pick up airborne vi-
brations. Living species of frog have such a membrane shaped like
a tiny drumhead, constructed of special skin. A deep notch in the
frog's skull holds the eardrum (known technically as a tympanum),
and between it and the brain stands an air-filled chamber: the mid-
dle ear. To transmit sound to the brain, a slender ear bone runs
from the eardrum to the canals of the ear in the side of the brain-
case. If it could be discovered when this type of ear first evolved,
it would constitute an important
clue about when the sexual chorus
first began.
The eardrum doesn't preserve in fossils, but the notch for it
in the skull does. Earliest of all amphibian fossils is the famous
Ichtbyostega from the lake beds of Greenland (its name means "fish
with a roof," a reference to its primitive fishlike structure and the
thick roof of its skull). This Ur-amphibian has no definite notch
for an ear, and couldn't have possessed any special auditory ad-
aptations. Therefore, when Ichthyostega and its kind waddled over
the primeval land, they must have marched into a silent world where
SEX AND INTIMIDATION: THE BODY LANGUAGE OF DINOSAURS | 327
the humid stillness was broken only by the rustling of ancient rushes
in the wind and the near-silent footsteps of Ur-spiders hunting in
the leaf mold.
But it did not take long for the fledgling land vertebrates to
evolve greater sensory complexity. Early in the Coal Age, quite
large notches for eardrums appeared prominently in the skulls of
the keyhole amphibians (loxommatids), a tribe of aggressive, sharply
fanged predators with alligatorlike skulls. ("Keyhole" refers to the
peculiar shape of their eye socket; an enlargement at the front of
it may have housed a gland.) Keyhole amphibians clearly could hear
airborne sounds, and therefore quite possibly used their voices to
bluff and challenge and court. Since their heads reached a length
of two and a half feet, they would surely have uttered a croak that
would command respect. Other ear-equipped amphibians evolved
Armor-plated bone-braced
amphibian eardrum holder.
The Early Permian Cacops
shows how amphibians
evolved a way to keep their
eardrums tight—a large
notch in the skull, just
behind the eye, acted as a
bony drum head. Cacops was
a land-living hunter, about
two feet long, and had bony
armor above its backbone,
but the same sort of
eardrum holder was
standard equipment in many
water-living amphibians too.
328 | THE WARM-BLOODED METRONOME OF EVOLUTION
Quick history of butting, bluff, and intimidation. It all started with the
evolution of eardrum skull notches in the Coal Age, proceded through the
Age of Finbacks in the Early Permian, and then up to the head-butters of the
Late Permian-Triassic, the tooting and butting Cretaceous-Jurassic dinosaurs,
and the modern mammals of the Cenozoic.
after them as the Coal Age continued, so the spring mating season
probably witnessed a diversified range of timbre and tone.
Reptile ears are built to the same general pattern as are am-
phibian ears, but the details of how the nerves pass through the
auditory apparatus are different. Most paleontologists presently
believe that reptiles evolved their ear independently and did not
simply inherit their auditory machinery from amphibian ancestors.
Today, the ears of lizards work much like the ears of frogs, but
the ears of Coal Age reptiles are biosonic puzzles. A good notch
for the eardrum evolved in some reptile tribes very early, yet the
bone of the middle ear was thick and ponderous, not the delicate,
thin bone absolutely required for hearing mid and high frequen-
cies. Massive ear bones wouldn't transmit most vibrations from the
eardrum to the brain, and some of these early reptile ear bones
are as big as a man's thumb. What could these ancient reptiles have
heard, if anything? It remains a mystery. Some anatomists have
suggested that the heavy ear bone was suspended by delicate lig-
aments and acted as a kind of seismograph for detecting very low-
frequency sound. This suggestion evokes visions of a mating dance
in which the courting couple stomps about producing minor earth
tremors to communicate their lust. Reptiles did not evolve ears of
high sensitivity until late in the Permian Period, long after the Coal
Age, and the Reptilia certainly weren't equipped to transmit and
receive airborne melodies before then.
Sex is not all melody. Pushing and shoving, intimidation, have
their place too. Frog suitors often try to kick their rivals off the
back of a female in the mating pond. The rhinoceros iguana lizard
of Cuba indulges in male-male wrestling contests. Males push each
other with their snouts, grab loose skin in their teeth, and may
clamp on each other's mouths in what is technically known as jaw
wrestling. Not many living amphibians have specialized organs for
sexual wrestling, but among the Coal Age fossils there is one
spectacular case.
Most amphibian skulls are designed quite straightforwardly.
With few exceptions, they can be explained in terms of jaw mus-
cles, bracing for teeth, sucking in prey underwater, or other purely
dietary needs. But diet can't explain the most grotesque amphib-
ians skull ever evolved—the boomerang-shaped head of Diplocau-
lus ("two-tailed," a reference to its double-spined tail bones).
330 | THE WARM-BLOODED METRONOME OF EVOLUTION
Battle of the boomerang-heads. Swoosh, clunk, and thud on a Texas stream
bottom during the Early Permian Period. Diplocaulus, a three-feet-long flat-
bodied amphibian, probably used its grotesque head horns for sideways
slugging matches. Eyes faced directly upward, so the underwater head-
bashing had to be done by touch.
The jaws, teeth, and face of this animal were quite "normal";
its snout was flat top to bottom and its eye sockets faced directly
upward. The animal was probably a pond and stream predator, lying
in ambush on the murky bottom, awaiting unwary prey. This was
an ecological role that evolved many times in separate amphibian
tribes. Probably all of Diplocaulus's life—including courtship and
mating—was spent underwater. Its young exhibited standard cra-
nial geometry for the role of bottom-predator: a generally wide,
rounded skull without significant protuberances. But as it grew into
adolescence, a transformation carried it into an exceedingly un-
usual development of the skull. The rear corners grew outward at
great speed. Well before it was fully adult, its skull had become
twice as wide as it was long. And even faster grew the hornlike
devices at the extreme ends, until at maturity the head was finally
four to six times wider than long. Viewed from the top, these heads
resembled nothing so much as organically grown boomerangs.
Paleontologists tried to explain the boomerang shape as an
adaptation for swimming; supposedly it worked like an underwa-
ter wing, imparting hydrodynamic life as the beast swam at high
speeds through the Coal Age streams. But Diplocaulus was not a
strong swimmer. Its body and tail were too flat to have borne the
muscles needed for fast underwater propulsion. So hypotheses based
on locomotion just don't seem plausible for the boomerang shape.
To my knowledge, no one has suggested an hypothesis based upon
sex and intimidation as the biological function that might make sense
o
f the grotesque cranial shape.
Diplocaulus was at a disadvantage in evolving organs for in-
timidating other members of its species. Its life was spent looking
up, so it couldn't easily see its neighbors lying alongside. It was
moreover an animal that lived in flat areas—hence its very low and
wide skull and body, no doubt to help it hide in ambush. And the
most vigorous movement available to it was rather awkward un-
dulation along the pond bottom. So how was evolution to work to
create a sexually impressive Diplocaulus} The evolution of intimi-
dation devices usually operates by modifying preexisting patterns.
Diplocaulus moved by wriggling across pond bottoms. During its
evolution, males and females must often have bumped into each
other in so doing. Genes that favored wider corners of the skull
could therefore yield an advantage. The longer the hornlike ex-
332 | THE WARM-BLOODED METRONOME OF EVOLUTION
tension, the greater the range of the bumping action. Boomerang-
heads couldn't see one another, but they could reach out and bump
someone.
While Diplocaulus was evolving in the waters of the Late Coal
Age and the following epochs of the Early Permian, evolution on
land was producing a spectacular show of its own. In water and on
land, walking tall has very frequently served as an effective sexual
advertisement. Several kinds of modern lizards grow exaggerated
spines from the backbone to provide themselves with a dominant
profile. The dorsal crests displayed by the Jesus lizards of Mexico,
for example, are impressive indeed. But none of this display can
compare with that of the long-spined clans that began in the Coal
Age. And most dramatic of the Permian finbacks was the predator
Dimetrodon, a genus that included species up to seven feet long.
Dimetrodon means "two sizes of tooth"—its razor-sharp dentures
varied from large fangs in front to short molars behind. Its jaws
were designed like Tyrannosaurus's (long before that creature saw
the light of day) and its lethal combination of jaws and teeth made
it the king of the Permian deltas.
However, Dimetrodon's formidable head was not its chief
characteristic. Far more impressive was the unusually long row of
spines rising from its neck, torso, and hips. Complete Dimetrodon
Robert T Bakker Page 33