Robert T Bakker Read online

  ther birdlike characteristics turned up in the dinosaurs' backbone.

  Many species of dinosaur had hollow chambers in their vertebrae.

  In life, these bony caverns were filled with air sacs connecting to

  the lung, just as in many birds today. Later nineteenth-century

  discoveries made the dinosaur-bird connection very intimate. Ar-

  chaeopteryx, the oldest fossil bird, was discovered in 1861 and made

  headlines because it looked so much like a small dinosaur with

  20 | THE CONQUERING COLD-BLOODS: A CONUNDRUM

  One of the first dinosaurs discovered—the thirty-foot predator Megalosaurus,

  dug up in the 1820s in England. Here the great megalosaur is attacking a sea

  crocodile, Te/eosaurus.

  In the 1860s Thomas Henry Huxley argued that birds descended from

  dinosaurs, and that view is now being revived—the six-feet-long predator

  Deinonychus, shown here attacking an ostrich dinosaur, is a near-perfect

  missing link between dinosaurs and modern birds.

  feathers. The great Darwinian orator and advocate Thomas Henry

  Huxley pounded the pulpit of evolutionary theory by pointing to

  Archaeopteryx as the missing link between dinosaurs and modern

  birds.

  It's important to be clear about the reverse definition as well:

  what dinosaurs are not. Dinosaurs are not lizards, and vice versa.

  Lizards are scaly reptiles of an ancient bloodline. The oldest liz-

  22 I THE CONQUERING COLD-BLOODS: A CONUNDRUM

  ards antedate the earliest dinosaurs by a full thirty million years.

  A few large lizards, such as the man-eating Komodo dragon, have

  been called "relicts of the dinosaur age," but this phrase is histor-

  ically incorrect. No lizard ever evolved the birdlike characteristics

  peculiar to each and every dinosaur. A big lizard never resembled

  a small dinosaur except for a few inconsequential details of the teeth.

  Lizards never walk with the erect, long-striding gait that distin-

  guishes the dinosaurlike ground birds today or the birdlike dino-

  saurs of the Mesozoic.

  Snakes are lizard nieces—descendants of a close relative of

  lizards. Some lizards have lost their limbs and slither like snakes,

  but true snakes have specialized eyes and jaws. Snakes, of course,

  are not at all close to dinosaurs.

  Crocodiles and their next of kin, alligators, are unquestiona-

  bly dinosaur uncles, relatives of dinosaur ancestors. Baron Cuvier,

  Sir Richard Owen, and other early dinosaurologists discerned many

  important anatomical characteristics shared by dinosaurs and croc-

  odiles. For example, dinosaur teeth are set in sockets—so are the

  teeth of crocodiles—whereas lizard and snake teeth are fused to

  the inside of the jawbone without sockets. Dinosaurs have a deep

  socket in the hip bones for the thigh, and so do crocodiles, but

  lizards do not. Crocodiles even show the beginnings of birdlike

  development in hip and thigh. Crocodiles first enter the chronicle

  of the rocks long after lizards but a few million years before di-

  nosaurs.

  Frogs and their short-legged relatives the salamanders are am-

  phibians, not reptiles. Amphibians lay water-breathing eggs, and

  usually the newly hatched young breathe via gills for a while be-

  fore becoming air-breathers. Like the reptiles, the amphibians have

  "cold blood." ("Cold blood" means that metabolism is so low that

  body temperature falls to air-ground temperature unless the ani-

  mal can heat up by basking in the sun.) Amphibians have only a

  very distant kinship to dinosaurs.

  Turtles are marvelous organic creations and very worthy ob-

  jects for contemplation, but turtles aren't dinosaurs. Turtles have

  a scaly skin and a leathery or porcelaneous egg, points of resem-

  blance to both lizards and crocodiles. But the body architecture of

  the turtle is so thoroughly unique that after nearly two centuries

  of research, turtle relationships are murky at best.

  Are dinosaurs true members of the reptile class? Good ques-

  BRONTOSAURUS IN THE GREAT HALL AT YALE I 23

  Bird, crocodile, and mammal adaptations combined—the three-ton

  herbivorous dinosaur lguanodon, first found in the 1820s in England. The

  spike of bone on the thumb must have been a dangerous weapon.

  tion. Hard to answer—that's what this book is all about. The late

  nineteenth-century naturalists defined Reptilia by blood, skin, and

  sex. If an animal had "cold blood," skin covered with scales, and

  laid eggs on land, then it was a true reptile. Despite the obvious

  similarities of design between crocodiles and birds, therefore, the

  scaly, naked hide of crocodiles and their "cold blood" have per-

  suaded most naturalists to separate them from the birds. Birds have

  their own class, the Aves. But crocodiles are left in the Reptilia

  with their more distant relatives, lizards, snakes, and turtles.

  Birds and mammals differ from each other in extraordinarily

  numerous ways, in nearly all details of their joints, muscles, and

  other organs. But birds and mammals do share two key adapta-

  tions which color their entire evolutionary style: both have insu-

  lation for the skin (feathers for birds, hair for mammals) and both

  are "warm-blooded" (they have such a high metabolic rate that their

  bodies are generally heated from the inside). Mammals have their

  own zoological class. Although the "warm-bloodedness" of birds

  and mammals is very similar in physiological detail, it is quite clear

  that the "warm-blooded" condition evolved separately, once in birds,

  once in mammals.

  Now, nineteenth-century science was self-consciously preoc-

  cupied with "progress." The Industrial Revolution had wrought

  such rapid advancement in machines, small and great, that mid-

  Victorian scientists could see no end to the upward perfection of

  technology. And Darwinism, in its vulgar "survival of the fittest"

  version, seemed to preach that there was a natural law guiding the

  continuous perfection of life forms through all geological time.

  Which was most perfect? Homo sapiens, of course—especially a male,

  English, Protestant Homo sapiens. And so our class, the Mammalia,

  had to be the highest zoological grouping. Birds were close be-

  cause, like mammals, they had insulation and metabolic control of

  their body temperature.

  Progress also meant freeing oneself from the uncomfortable

  whims of the environment—the sudden changes in heat and light.

  The poor reptile could bask happily on a rock in the sun but slipped

  back into a chilled torpor when clouds blotted out the warming

  rays. Not so the bird or mammal whose body furnaces burned so

  fast and so continually that blood and flesh remained warm. And

  Victorian biochemistry had progressed far enough to discover that

  BRONTOSAURUS IN THE GREAT HALL AT YALE | 25

  most vital processes function best when the body temperature is

  nearly constant. English homes—upper-class ones, at least—were

  enjoying the dependable warmth of coal-fed furnaces, devices that

  finally made the damp winter climate cozy and comfortable. Clearly

&n
bsp; the highest zoological classes were the ones that had evolved an

  analogous metabolic adaptation.

  The zoologists of the last century knew well that there was a

  case for a crocodile—bird relationship and an even better case for

  a dinosaur—bird kinship. But the scientists of the time nonetheless

  slipped into the habit of calling dinosaurs "reptiles!'—cold-blooded,

  scaly creatures that laid eggs.

  Nineteenth-century naturalists used their warm blood/cold

  blood dichotomy to classify all vertebrates into two grand divi-

  Two ways dinosaurs

  could be classified—as

  cold-bloods because

  dinosaurs share

  adaptations with

  crocodiles, or as warm-

  bloods because

  dinosaurs have many

  birdlike features.

  26 I THE CONQUERING COLD-BLOODS: A CONUNDRUM

  sions, one above the other. At the bottom were the "lower ver-

  tebrates," the classes without metabolic control of their body heat.

  Here were lumped all the fishes, the Amphibia, and of course the

  Reptilia. At the top were the "higher vertebrates," the two classes—

  Aves and Mammalia. Dinosaurs were thrown into the Reptilia and

  so into the "lower vertebrates" by early naturalists, but an equally

  good case could have been made to classify dinosaurs as primitive

  birds. No one, either in the nineteenth century or the twentieth,

  has ever built a persuasive case proving that dinosaurs as a whole

  were more like reptilian crocodiles than warm-blooded birds. No

  one has done this because it can't be done.

  Generally speaking badges are harmful in science. If a scien-

  tist pins one labeled "Reptile" on some extinct species, anyone who

  sees it will automatically think, "Reptile, hmmm . . . that means

  cold-blooded, a lower vertebrate, sluggish when the weather is dark

  and cool." There are never enough naturalists around, in any age;

  so most scientific orthodoxy goes unchallenged. There are just not

  enough skeptical minds to stare at each badge and ask the embar-

  rassing question, "How do you know the label is right?"

  Be kind to colleagues, ruthless with theories, is a good rule.

  A scientific theory isn't merely idle speculation, it's a verbal pic-

  ture of how things might work, how a system in nature might or-

  ganize things—atoms and molecules, species and ecosystems. But

  old paleontological theories too often aren't treated roughly enough.

  Old theories—like the reptilian nature of dinosaurs—are accepted

  like old friends of the family. You don't yell at old Aunt Cecilia.

  So hundred-year-old dinosaur theories live on without being

  questioned, and too often they are assumed to be totally correct.

  Even when such theory is caught in an error, it's likely to be

  excused.

  Traditional dinosaur theory is full of short circuits. Like the

  antiquated wiring in an overaged house, the details sputter and burn

  out when specific parts are tested. I have enormous respect for

  dinosaur paleontologists past and present. But on average, for the

  last fifty years, the field hasn't tested dinosaur orthodoxy severely

  enough.

  I'd be disappointed if this book didn't make some people an-

  gry. A lot of modern scientists—even some paleontologists—in-

  sist on saying that fossils are misleading. "Dead bones don't

  BRONTOSAURUS IN THE GREAT HALL AT YALE I 27

  metabolize so how can physiology in dinosaurs be discussed?"

  Ecologists who study the Serengeti Plain or the rain forests of

  Burma are impressed by the complex ways animal species interact

  with each other and with their habitats: "How can a few spare bones

  capture all the organic subtlety of long-extinct systems?" Many

  people dismiss the record of the rocks as an incomplete and nearly

  unreadable document. Darwin himself did that; he didn't trust fos-

  sils to indicate the entire truth. But these views are wrongheaded.

  The Book of Job—oldest in the Bible—admonishes, "Speak to the

  Earth and it will teach thee." If we look and listen carefully, the

  record of the rocks can unlock the richly textured story of the di-

  nosaurs and their ways.

  The Stonesfield specter. From the very first discoveries of dinosaurs in the

  1820s there was proof positive that our mammalian order had existed under

  the shadow of the gigantic dinosaurian monsters. Earliest of the dinosaur

  quarries was the road-gravel pit in the Stonesfield Slate, where giant jaws of

  Megalosaurus could be found with teeth so large that a single tooth was

  longer than the entire jaw of the mammals found in the same strata. Shown

  here, natural size, is Phascolotherium standing next to the lower jaw of

  Megalosaurus.

  28 | THE CONQUERING COLD-BLOODS: A CONUNDRUM

  2

  WYOMING REVERIE:

  MEDITATION ON THE

  GEOLOGICAL TEXT

  From my Field Book, 1981

  July 3, 6:35 A.M.

  Como Bluff, Wyoming. 7,020 feet above sea level. No human being

  or human structure visible. Air clear, dry, cool. A pair of mule

  deer browsing along Rock Creek. Put the coffee water on the

  Coleman stove to heat up. No one else is awake in camp yet, but

  the smell of bacon will entice them out of their tents.

  I have been in the business for twenty years—digging up fos-

  sil bones—but I'm still excited by the first dinosaur of the sum-

  mer. I sit here on the crest of a little sandstone hogback, remnant

  of a stream that flowed a hundred million years ago, and look down

  on my crew's work of the last four days. It's becoming a sizeable

  hole, a proper dinosaur dig, twenty-five feet across, dug by pickax,

  army-surplus trenching shovel, icepick, and fingernails.

  I saw my first dinosaur in that splendid Mecca for Mesozoic

  relics, the American Museum of Natural History in New York, at

  the age of nine. But those skeletons seemed tamed by civilization,

  mounted as they were on steel and plaster, posed for the benefit

  of countless parades of schoolchildren and tourists. A dinosaur in

  the rock is different. This one before me is huge, and its six-foot-

  long thigh bone, which would dwarf any elephant's, lies half ex-

  posed to the Wyoming sunrise. Its coal black form is clearly etched

  WYOMING REVERIE: MEDITATION ON THE GEOLOGICAL TEXT I 29

  The great dinosaur graveyards

  of the American West

  against the surrounding pale rock by thousands of careful chisel

  marks. This bone is a holy relic for me, as beautiful in its roughly

  hewn outline as Michelangelo's bound slaves struggling to free

  themselves from the enveloping marble.

  From where I sit on the quarry's rim I can see the dinosaur's

  great trochanters, the attachment site of the immense hip muscles,

  and the bone surface pitted and rough where tendons and liga-

  ments were anchored to the femur. A hundred thousand millennia

  ago, those tendons and muscles were full of dinosaur blood cours-

  ing through capillary beds, bringing oxygen to the cells that pow-

  ered the stride of this ten-ton giant. Muscles pulsed in cycles of
r />   contraction and release, and the hind limb, fully twelve feet long

  from hip to toenails, swung through its stroke covering six feet

  with every pace.

  Broken chips of bone lie under my boots, wretched frag-

  ments from now unidentifiable bones which had eroded long be-

  fore we found the site. Even though I know I can't identify the

  bits of bone, I pick one up anyway because there is something

  special about the feel of dinosaur bone very early in the morning.

  Some of the broken bits are incredibly delicate bubbles of bone,

  a frothy texture of holes and vesicles that housed the living sub-

  stance of the animal's cells. These bits crumble into shards if I rub

  them too hard, but in life the brittle bone crystals were embedded

  in a fabric of tough connective tissue, collagen fibers whose great

  tensile strength combined with the hardness of the bone crystals

  to produce a living bony architecture capable of resisting enor-

  mous loads of both compression and tension. Collagen has long

  since rotted away, along with all the muscle fibers and blood ves-

  sels. But the fossilized bone faithfully preserves the canals left by

  every capillary that made its passage through it to serve the dino-

  saur in life. Those living cells, now gone, left one other signature

  on this carcass. A black powder rubs into my gloves as I finger the

  bone chips. This powder is carbon dust mixed with granulated bone,

  the dried and distilled residue of all the cell membranes, cell fluids,

  and organelles whose work within the bone was ended when the

  dinosaur died.

  Reverie is normal in Wyoming at sunrise. I suppose a no-

  nonsense laboratory scientist, clad in his white lab coat and steely-

  eyed objectivity, might think I was wasting my time communing

  WYOMING REVERIE: MEDITATION ON THE GEOLOGICAL TEXT I 31

  Our camp at Como Bluff and how the rock layers would look if cut through

  vertically

  with the spirit of the fossil beast. But scientists need reverie. We

  need long walks and quiet times at the quarry to let the whole

  pattern of fossil history sink into our consciousness.

  As I walk back to camp from the quarry, I climb through the

  ledges of hard rock, benches of limestone, each an irregular mo-

  saic of ovoid nodules, each extremely hard and long-lasting in this