Robert T Bakker Read online

  head and the prey's limbs point away. Then the snake opens its

  jaws and begins to engulf the monkey. Not hurriedly, not with

  crude gulping and gnashing of teeth, but deliberately and pre-

  cisely, the snake draws the monkey's head and shoulders into its

  mouth. We humans are limited by our rigid and brittle jaw, whose

  right and left sides are firmly joined at the chin so that the width

  of our mouth is fixed. The right and left halves of the serpent's

  jaw are joined only by an elastic ligament, so the "chin" can stretch

  MESOZOIC CLASS WARFARE: COLD-BLOODS VERSUS THE FABULOUS FURBALLS | 71

  as the monkey's head is swallowed. Within both right and left lower

  jaw, the snake possesses a hinge that allows even more expansion.

  Our human jaws move sideways only slightly where they meet the

  skull at the jaw joint, just in front of the ears (try moving your

  jaw from side to side with your finger resting on the jaw joint—

  you will feel only about Va" of movement). But the right and left

  halves of the snake's jaw are hung on the skull by a long, folding

  strut, divided into two hinged sections like a carpenter's ruler. As

  the snake engulfs the monkey's shoulders, these joints swing out-

  ward on their flexible struts, enormously increasing the gullet's di-

  ameter to accommodate the outsized prey.

  So far we have witnessed only the passive aspect of the puff

  adder's swallowing act—the hinges and elastic joints being pushed

  out by the prey's body as it is drawn into the snake's mouth. But

  the greater marvel is the way the snake powers its jaws to drag the

  prey down its throat. We think of swallowing as a minor muscular

  feat. We chew a few dozen times and gulp. Down goes a little

  masticated food accompanied by minor contractions of our tongue

  and esophageal apparatus. Our chewing muscles do most of the

  work; swallowing is not a major event. But since snakes don't chew,

  the entire body of the monkey is actively drawn into the snake's

  throat by the backward pull of fanged jaw bars, two above and two

  below. Unlike the soft roof of our mouth, the snake's palate pos-

  sesses bars of bones, studded with backwardly curved teeth, on

  each side. The snake's jaw muscles can manipulate each palate bar

  backward by itself, the recurved teeth dragging the prey backward

  into the throat. After the bar has pulled as far backward as it can

  go, the jaw muscles lift it up and forward, while disengaging the

  curved teeth from the prey, and move the bar forward to start an-

  other stroke. The lower jaws can also be retracted independently,

  one side at a time, to aid in dragging the monkey down its throat.

  To get a mental picture of the process as it might work in our

  heads, imagine that your jaw could expand at chin and jaw joint;

  imagine that you had two short hands, each holding a fork, at-

  tached to the roof of your mouth. You have a big monkey on your

  plate. You wrap your expandable jaws around it and your palate-

  forks stuff it down your throat in alternated strokes until the whole

  monkey carcass slides down. Finally, only the monkey's tail can be

  seen disappearing into your mouth.

  72 I THE CONQUERING COLD-BLOODS: A CONUNDRUM

  No other land vertebrate today swallows more elegantly than

  the snakes. Serpent success—nearly three thousand living spe-

  cies—surely owes much to this sophisticated machinery for diges-

  tion, which allows snakes to exploit very large prey relative to their

  own body size. Human evolution produced a rather dull, simple

  jaw apparatus. Our brain size permitted us to compensate by in-

  venting stone knives, steel carving sets, and Cuisinarts, so we can

  take a whole steer and swallow it, piece by piece. We should ad-

  mire how evolution has solved this prey-bigger-than-your-head

  problem in snakes with entirely internal adaptations.

  How the boa head works.

  In the roof of the mouth

  the two double-tooth rows

  move alternately—the left

  side pulls the prey backward

  down the throat as the right

  side reaches forward, and

  vice versa. To expand the

  gullet, all the cranial joints

  bend outward: The rear jaw

  strut swings out, the joint in

  each lower jaw flexes, and

  the right and left lower jaws

  stretch apart at the chin.

  MESOZOIC CLASS WARFARE: COLD-BLOODS VERSUS THE FABULOUS FURBALLS | 73

  Panzercrocs—the exception that proves the rule.

  During the Age of Mammals, very few cold-

  blooded reptiles evolved large size and aggressive

  habits and challenged the warm-blooded Mammalia.

  An exception was the Panzercroc— Pristichampsus—

  an eight-feet-long crocodilian that evolved long,

  fast-running legs and hooflike claws for land

  locomotion and steak-knife—like teeth for killing

  and cutting up mammal prey (shown here is the

  Dawn Horse, Eohippus). Pristichampsus hunted

  during the Eocene Epoch, about 49 million years

  ago, but it was very rare, much rarer than big

  mammalian predators, proof that cold-bloodedness

  was a great disadvantage.

  4

  DINOSAURS SCORE WHERE

  KOMODO DRAGONS FAIL

  inosaurs must be viewed as a giant evolutionary system, a vast

  D conglomerate of species who shared a common adaptive plan.

  No adaptive plan is perfect—neither warm-bloodedness nor cold-

  bloodedness, for example, works best all the time. If we probe the

  nature of the dinosaurs' success, we can feel out the basic strengths

  and weaknesses that existed within the dinosaurian organization.

  And that will allow us to understand more about precisely what

  kind of animals they were.

  Orthodox theory has it that dinosaurs were merely "good

  reptiles," essentially scaled-up versions of modern lizards and crocs

  whose metabolism was pitifully low compared to mammals'. So we

  can begin our inquiry into the nature of the dinosaurs' success by

  asking, What are the limitations of the cold-blooded reptiles—where

  do they fail today? As we saw in the previous chapter, reptiles and

  amphibians do overwhelmingly outscore mammals in total species

  count. But it must also be said that there are ecological categories

  where the cold-blooded league is almost entirely shut out. If the

  basic organization of the dinosaurs really was reptilian, then the

  pattern of deficiencies we observe in today's Reptilia should match

  the picture we get from the dinosaurian world. But what if the

  dinosaurs' successes turn out to be totally different from those of

  modern reptiles? What would that mean for the orthodox theory?

  If we discover that dinosaurs succeeded where modern reptiles fail,

  and vice versa, then such a theory would be totally incorrect.

  DINOSAURS SCORE WHERE KOMODO DRAGONS FAIL | 75

  Why body temperature is so important. All physiological performance peaks

  at one narrow temperature range, and the whole body machinery slows down

  when body temperature falls. Many lizards are at peak form at a body


  temperature close to a human's—about 98 degrees F. But when body

  temperature drops 10 degrees C (18 degrees F), performance drops to half—

  running speed is half as fast and digestion takes twice as long. When

  temperature drops another 10 degrees C, performance falls to only one

  quarter of the peak levels.

  Super-giant tortoise— Colossochelys. Today a big Galapagos tortoise can reach

  fifty inches long (measured front to back on the bottom shell) and five

  hundred pounds. But a few million years ago Colossochelys grew to eighty

  inches and four tons or more. Shown here is the profile of a five-hundred-

  pounder with rider and, in silhouette, the giant Colossochelys.

  In this chapter we can begin by considering the reptilian giants

  that came after the end of the Cretaceous, after the end of the

  dinosaurs. These cold-blooded monsters evolved during the Age

  of Mammals. Their story teaches many lessons about reptilian fail-

  ure. Colossochelys, the king of the giant tortoises, presents one such

  lesson. Bones from the two-million-year-old sediment of the Si-

  walik Hills in India contain fragments of elephant, hyena, hippo,

  bear—and of Colossochelys. The fossils of the tortoise king has been

  found everywhere in the Old World tropics, from Kenya to Cape

  Province to Java (fragments suggest its presence in Florida, too,

  during this age). Everywhere it was found, there was an accom-

  panying rich fauna of big, modern-type mammals. Complete Co-

  lossochelys shells are one of the most breathtaking displays in all of

  terrestrial turtledom. They look like fossilized Volkswagen Bee-

  tles, enormous bone domes six feet long and three feet high. When

  alive and fully grown, Colossochelys dwarfed even the largest giant

  tortoise alive today.

  DINOSAURS SCORE WHERE KOMODO DRAGONS FAIL I 77

  Tortoises are paradoxical reptiles. Their history is a success

  story, but they also betray the basic flaws in the economic orga-

  nization of the Reptilia. Tortoises constitute a family of the turtle

  group, and represent the acme of turtle adaptation to dry-land

  habitats. Their feet are super-compact, with short toes and ele-

  phantlike cushion pads, and their beaks enable them to crop grass

  like a cow (most other modern reptiles are carnivores). Tortoises

  aren't an ancient tribe at all; the first tortoise didn't evolve until

  the Eocene Epoch of the Age of Mammals, fifteen million years

  after the last dinosaur died. So tortoises are one of the very last

  big-bodied reptiles to make their appearance. And their dome-

  shelled clan scored major ecological successes for forty-five mil-

  lion years despite the potential danger from mammalian meat-eat-

  ers and plant-eaters.

  Giant tortoises could defeat any mammalian predator except

  one—man. Because of man, two-ton tortoises are totally extinct

  today and even the three-hundred-pounders are very rare, re-

  stricted to a few desert islands—the Galapagos off Ecuador and

  the Aldabras in the Indian Ocean. The demise of the giant tor-

  toises is thus a very recent event for which our own species is

  probably to blame. One human hunter couldn't kill a giant tor-

  toise easily, but six together could use a branch to tip the tortoise

  on its back, then build a fire under its shell, and stew the poor

  beast in its own carapace. Human hunters were a very late devel-

  opment in the Age of Mammals, and they started multiplying sig-

  nificantly only in the last two million years. But once they got going,

  our primordial forefathers cut a wide swath through both the Old

  World and the New, exterminating dozens of big species of mam-

  mal—mammoths, mastodons, saber-toothed cats, giant ground

  sloths, to name but a few. And they killed giant tortoises. That

  must not allow us to forget the remarkable success of giant tor-

  toises up till the advent of human hunters. The best nonhuman

  predators couldn't kill off the big tortoises; saber-toothed cats, giant

  bears, oversized hyenas, clever wolves, all in their heyday failed to

  suppress Colossochelys.

  These giant tortoises demonstrate that cold-blooded reptiles

  could handle mammalian enemies (nonhuman ones). But their

  manner of success also reveals the limitations of the reptile's adap-

  tive equipment. Tortoises were "cold-blooded" in the narrow,

  78 | THE CONQUERING COLD-BLOODS: A CONUNDRUM

  physiological sense of the word: they had very low metabolism

  compared to that of a mammal of the same size. A tortoise could

  heat up its body tissue only if it had access to abundant solar en-

  ergy in the form of direct sunlight or solar-warmed sand or rocks.

  Tortoises were also typically reptilian in the small size of their heart

  and lungs. They couldn't keep up a level of activity anywhere nearly

  as high as a dog, bear, or hyena could. How, then, could the tor-

  toise overcome the debilitating effects of its low metabolic perfor-

  mance? Armor. Quite simply, tortoises succeeded because they

  didn't confront mammals in direct tests of strength and coordina-

  tion. Tortoises didn't have to flee the lions the way wildebeest do

  today, with a burst of high speed. And tortoises didn't have to de-

  fend themselves the way wild boar do, with aggressive counterat-

  tacks. When threatened, the tortoise simply pulled in all its

  appendages—head, tail, and legs—and waited out the danger, with

  vulnerable body tissue withdrawn into its incredibly strong bony

  shell. If it had to, a giant tortoise could wait for hours, for days,

  even for months, because its low metabolism allowed long fasts.

  Tortoises beat mammal attacks by a totally passive defense. There's

  a lesson here, one that orthodox paleontologists ignore: When

  warm-blooded mammals abound, reptiles can't evolve large size on

  land unless very special adaptations permit the reptiles to avoid

  direct confrontation.

  In the very same tropical woodlands and bush where giant

  tortoises flourished for so long, another exceptional reptilian

  evolved—the giant land snake. Big snakes labor under the same

  limitations as tortoises when faced by mammal predators. Giant

  pythons have a low metabolism so they can't keep their bodies warm

  if solar heat isn't abundant. Their heart and lungs are low-powered

  affairs compared to the typical mammalian design. And snakes can't

  compete in prolonged contests of violent activity. How, then, do

  giant snakes survive among the lions and hyenas? By stealth and

  patience. Giant snakes don't try to compete with hyenas in run-

  ning down antelope over long chases. They don't prowl over

  hundreds of acres the way lions do. A twenty-foot python glides

  silently out of its hole near a waterhole's edge and lies in wait,

  concealed by its camouflaged hide and long, low silhouette. Here

  again, the low reptilian metabolism permits the giant snake to wait

  as no mammal could, for weeks if necessary. Finally, an unwary

  DINOSAURS SCORE WHERE KOMODO DRAGONS FAIL I 79

  antelope comes to drink and steps too close to the python. In one

  moti
on two hundred pounds of snake coil around the antelope's

  chest. The snake kills by subtle alterations of its grip, not by vio-

  lent contractions. The snake's body musculature can't work a tenth

  as hard as a lion's over an hour's time. But by contracting every

  time the antelope exhales, the snake's coils can finally tighten into

  a suffocating straitjacket.

  Big snakes, like big tortoises, deserve credit for their success

  in the Age of Mammals. Giant land snakes have hunted mammals

  in all tropical continents for the last thirty million years. But we

  can see that their success comes only by avoiding mammal-style

  hunting tactics. The great serpents succeed by being something a

  warm-blooded mammal could never be—a hunter of infinite pa-

  tience, with a legless body designed for maximally cryptic loco-

  motion and ambush.

  Is there any reptile which has successfully challenged large land

  mammals for the role of normal, four-footed predator? The Ko-

  modo dragon lizard is a possible candidate. Orthodox paleontolo-

  gists often point 'to the Komodo dragon as the perfect modern

  analogue of the dinosaurs—a big terrestrial reptile that succeeds

  in dominating a warm tropical ecosystem. But the. Komodo dragon

  is a red herring.

  The truth about it helps demonstrate that the dinosaurs' suc-

  cess couldn't possibly be the result of a lizard-style metabolism.

  Komodo dragons, it is true, can kill the largest land mammals on

  Komodo—even adult horses and water buffalo. But the dragon rules

  a kingdom of tiny extent. No dragons survive on the nearby big

  islands of Java or Sumatra. Dragons swim well and could easily get

  to these bigger areas, yet their entire breeding population remains

  restricted to a handful of tiny islands. And unlike the tortoises,

  these dragons in the past have never extended to the big islands

  and mainland areas. There's an obvious explanation for these geo-

  graphical limitations.' The dragon succeeds only where it's free from

  interference from large mammal predators. Leopards, tigers, and

  sun bears prowl the big Indonesian islands, and there were large

  hyenas too until a few million years ago. The mainland of South-

  east Asia has hosted big cats, wolves, and hyenas in dangerous

  profusion. On Komodo Island not one large mammal predator has