Robert T Bakker

by The Dinosaur Heresies (pdf)

position it occupies in modern opinion. Dimorphodon's sharp teeth

  jutted directly upward from the lower jaw and directly downward

  from the upper. Therefore its strong bite must have been deliv-

  ered by a quick, simple snap of uppers and lowers together.

  But Dimorphodon's prey-catching devices weren't limited to that

  simple snap of the fangs. Dimorphodon % neck was also constructed

  to deliver rapid lunges. All pterodactyl necks were long and grace-

  ful, and all had joints between the vertebrae of the neck which

  allowed their owners to hold their head and neck in an S-shaped

  curve. Since they all possessed large skulls compared to their body

  size, this S-shaped curve allowed them to fly with their heavy heads

  held far back over their shoulders. And this posture permitted

  better distribution of weight both for flight and for walking, ex-

  actly as modern pelicans tuck their big heads over their shoulders

  DINOSAURS TAKE TO THE AIR | 283

  Rhampkorhynchus

  to gain better balance. But the S-shaped neck also provided Di-

  morphodon with the ability to lunge; it could rapidly flip its head

  and neck forward to make a quick grab at prey.

  Other early pterodactyls shared the Dimorphodon's basic de-

  sign but with variations. One Italian species had three-cusped mo-

  lar teeth interspersed with tall fangs—a very strange arrangement—

  crowded together along its jaws. The entire row of teeth could slice

  fish into strips in a matter of seconds. Swallowing big prey is a

  challenging biomechanical problem for today's shorebirds, be-

  cause most can't easily tear up fish carcasses with their beaks, and

  speed is of the essence because there are always thieves around

  trying to run off with the prey. Most birds solve this problem the

  same way dinosaurs did—the joints of the skull and jaws expand

  sideways to enlarge the gullet's capacity. Pterodactyls faced the

  problem but couldn't expand the rear of their jaws because the

  skull's bones were too tightly knit. However, at the halfway point

  of their lower jaws there was a zone of weakness that might have

  allowed the jaws to bow outward so a large fish could slip down

  the throat.

  Fish and squid are tricky prey for an aerial hunter. These quick-

  moving, slippery creatures can detect a pelican or puffin's dive just

  before it strikes the water, and the whole school of them may scatter

  in all directions. The pterodactyl's hunting tactics evolved to max-

  imize the quickness of its strike. In the lustrous, lithographic lime-

  stone of Bavaria are preserved the Late Jurassic squadrons of flying

  dragons arrayed with a wide variety of head and body shapes. Still

  in evidence are the straight-toothed biters similar to Dimorphodon

  in design. But other tribes exhibit features for a tactic newly evolved

  among flying reptiles—spearing with the head. Most numerous of

  the tern-sized Bavarian pterodactyls is spear-headed Rhampho-

  rhynchus ("beaked-jaws"). The S-shaped neck of primitive ptero-

  dactyls was accentuated in this animal so that the head could be

  carried coiled tightly against the shoulders. Rbamphorhynchus had

  jaws and teeth shaped exactly like the fishing spears used by some

  Amazonian Indian tribes today. Long, sharply tapered teeth in both

  its upper and lower jaws were bent forward, so all the points would

  converge to form a thrusting fish trap. Even the tip of the snout

  and chin tapered to deadly points to form the apex of the spear.

  Amazonian Indians hurl their spears at the heads of the fish: the

  DINOSAURS TAKE TO THE AIR | 285

  intermeshing set of points snags the fish's body, and its struggles

  to escape only serve to drive the barbs in more deeply. Just so

  Rhamphorhynchus could dive toward a fish, suddenly uncoil its S-

  shaped neck flexure, and hurl its spear-shaped head at its prey,

  impaling a hapless fish in the intermeshing barbs. This aerial fish-

  ing spear must be ranked as one of the most effective fish traps

  ever to evolve.

  Baron Cuvier's Pterodactylus hunted for its daily ration in the

  same reef-fringed waters as Rhamphorhynchus. But it had a totally

  different apparatus for snaring prey. Extremely long, gently taper-

  ing jaws terminated in a cluster of short, straight teeth. Pterodac-

  tylus % jaws looked just like the barbed tweezers used to manipulate

  squirmy invertebrates in today's zoology labs. And quite possibly

  Pterodactylus was an airborne worm tweezer. It may well have

  probed the sand flats like a Jurassic sandpiper, poking its long snout

  into the burrows of polychaete worms, shrimplike crustaceans, and

  sand fleas.

  There's excellent evidence that one rather rare Argentine

  species, the bristle-toothed pterodactyl, pursued a flamingolike style

  of life. Modern flamingos derive their pink coloration from the

  pigments stored in the tiny shrimplike creatures they filter from

  the shallow salty waters. The shrimp, in turn, get this pigment from

  tiny algae that they filter through their leg bristles. Captive fla-

  mingos fade to off-white when given prepared zoo food, much to

  the disappointment of curators and public alike. Fortunately, the

  natural pigment can be replaced by simple food coloring (the same

  kind used to dye Easter eggs) added to the flamingo's diet, so most

  zoos can keep their birds in the pink. Shrimplike crustaceans are

  a very ancient group, as are the red algae that are the ultimate

  suppliers of the pigment. Salty pools must have hosted red algae

  blooms in Jurassic days exactly as they do today. Then, as now,

  both algae and shrimp were an excellent source of food for any

  larger animal equipped to sieve them out of the water through an

  anatomical strainer. Was there, then, a pink strainer pterodactyl?

  Probably. The Argentine pterodactyl in question possessed a fla-

  mingo-shaped mouth with a dense row of thin, bristlelike teeth.

  Without question this bristle-toothed pterodactyl pumped water

  through its mouth with its tongue, straining out tiny food particles

  in the process. And since blooms of red algae were common in

  286 | DEFENSE, LOCOMOTION, AND THE CASE FOR WARM-BLOODED DINOSAURS

  Rhamphorhynchus fishing technique

  briny water, it's reasonable to suppose it would often filter both

  algae and shrimp, and behold, a pink pterodactyl!

  Flamingos appear especially awkward when they are hard at

  work feeding because their filtering bristles are in the upper jaw

  and their head must be upside down to perform its function in the

  water. Bristle-toothed pterodactyls didn't have to perform head-

  stands, because their filtering apparatus was located in the lower

  jaw, so the head could be lowered right side up into the water.

  Curiously enough, flamingos and bristle-toothed pterodactyls aren't

  the only examples of algae-straining aerialists to evolve in the his-

  tory of life. Forty-five million years ago a long-legged duck with

  flamingolike bristles in its lower jaw waded through the salty lakes

  of Wyoming, Colorado, and Utah. Fossil beds laid down in these

&n
bsp; briny lakes preserve the skulls, skeletons, footprints, and even some

  mound-type nests and the eggshells of the bristle-beaked duck.

  These three filter feeders are an extraordinary example of how

  evolutionary processes can shape unrelated clans into one and the

  same specialized ecological mode.

  While on the subject of color, Dimorphodons snout deserves

  DINOSAURS TAKE TO THE AIR

  287

  comment. Seeley reconstructed this animal with a dark snout. But

  more likely Dimorphodon's face was positively gaudy. Its high-

  snouted profile was more like a puffin's than that of any other bird,

  and puffins employ their tall beaks to advertise their social status.

  Juvenile puffins start out quite drab in the snout, but adults are

  marked by faces run riot with white, red, and orange stripes and

  splotches. Dimorphodon % deep snout cannot be explained by any

  hypothesis involving its jaw muscles or teeth. It's quite likely that

  Dimorphodon % snout evolved its unique high contours to advertise

  its owner's rank in pterodactyl society. Since pterodactyls were

  highly visual creatures, with large eyes and bulbous optic hemi-

  spheres in their brain, it's very probable in fact that colorful de-

  vices evolved many times among the various branches of the family

  The flamingo pterosaur

  —Pterodaustro from

  Argentina

  tree. Of course there is no direct evidence allowing reconstruction

  of the color pattern for any particular species of pterodactyl, but

  their color must have evolved to brighten Jurassic and Cretaceous

  skies in many ways.

  Everywhere in the world's ecosystems the transition from the

  Jurassic to the Cretaceous was marked as a time of disaster, dis-

  turbance, and extinction. Flying dragons did not escape this vast

  ecological shake-up. The experts divide all pterodactyls into two

  great tribes: the long-tails and the short-tails. After the Late Juras-

  sic extinctions wiped out most of the previously dominant long-

  tails, the short-tailed species moved in to fill the Cretaceous skies.

  Rhampborhynchus, with its fishing-spear head, was a long-tail; Baron

  Cuvier's Pterodactylus was a representative short-tail. By and large

  the long-tailed species did have fairly long tails—and at least some

  of them possessed kitelike tail rudders. Professor Othniel Marsh

  of Yale bought a superb Rhampborhynchus from German fossil

  dealers in the 1880s and subsequently announced to the envious

  Europeans that his skeleton possessed a tail rudder, previously un-

  known. Rhampborhynchus carried a vertical diamond-shaped fin at

  the end of its very long tail. The fin consisted of tough skin rein-

  forced by rods of connective tissue. The entire tail could be en-

  ergetically swished by muscles at the base of the tail. The precise

  aerodynamic effects of this intriguing equipment aren't yet under-

  stood, but the kite-tailed pterodactyl must have exercised precise

  control over its maneuvers, at least at slow speeds.

  Short-tailed pterodactyls generally had more specialized skulls,

  longer necks, and longer forearms than their long-tailed fore-

  bears—implying a fundamental change (still not well understood)

  in flight mechanics. This short-tailed Cretaceous dynasty certainly

  won an undisputed place in the book of aerial records, for it in-

  cluded the largest flying creatures ever to evolve. Marsh made

  headlines in the 1880s when he announced short-tailed pterodac-

  tyls from Kansas with wingspans of twenty feet or more. But the

  mind-boggling pterodactyl was yet to come. In the 1970s, Profes-

  sor Wann Langston led teams from the University of Texas into

  the scorching badlands of Big Bend National Park where the Rio

  Grande makes its huge loop on its way to the Gulf of Mexico.

  When Langston discovered a Cretaceous pterodactyl at Big Bend,

  its upper arm bone measured twice the size of the next-largest

  DINOSAURS TAKE TO THE AIR | 289

  known, and its jaws indicated a head eight feet long. Preliminary

  reconstruction, based on the wing plans of smaller species, pro-

  duced an estimated wingspan of up to twenty meters—sixty-three

  feet, greater than the wingspan of the old twin-engine DC-3 air-

  liners. Quetzalcoatlus was featured on the cover of Science, the most

  widely read scholarly journal in the United States. Immediately after

  their paper came out in Science, Wann Langston and his students

  were attacked by aeronautical engineers who simply would not

  believe that the Big Bend dragon had a wingspan of forty feet or

  more. Such dimensions broke all the rules of flight engineering: a

  creature that large would have broken its arm bones if it tried to

  fly. Quite a flap erupted over whether the Big 3end pterodactyl

  could even have powered its wings in the up-and-down strokes

  necessary for active flight. Under this hail of disbelief, Langston

  and his crew backed off somewhat. Since the complete wing bones

  hadn't been discovered, it was possible to reconstruct the Big Bend

  pterodactyl with wings much shorter than fifty feet.

  I believe Langston and his Texans were right—the Big Bend

  aerial leviathan was stupefyingly large. Mechanical engineers go

  often astray when analyzing the strength of skeletons. The most

  common difficulty with their method is that they calculate the

  strength of an arm bone as though the bone by itself had to with-

  stand all the stresses of flapping the wings. If the pterodactyl were

  a man-made machine, the wing skeleton would indeed bear all the

  stress. But naturally evolved arms are far superior to mechanical

  ones. The bundles of muscles sheathing the arm bones of birds or

  humans contract to reorient stresses when the body is exercising

  vigorously. Such contractions are automatic, since the muscles are

  sent a constant flow of orders from the posture-control centers of

  the nervous system. Therefore a live Quetzalcoatlus was stronger

  than an engineering analysis of its bones might indicate. More-

  over, calculating the stresses in a sixty-foot pterodactyl's wing is

  also subject to extreme variation—the Big Bend animal may well

  have flapped its wing from the wrist and not from the shoulder,

  for example. And in fact until the joints of the wing are clearly

  understood, any attempt to calculate stresses remains dubious at

  best. In general, I believe it dangerous to argue a priori that

  Quetzalcoatlus couldn't have been as big as seems indicated. The

  theories of bioengineering relating to flight in live mammals are

  290 | DEFENSE, LOCOMOTION, AND THE CASE FOR WARM-BLOODED DINOSAURS

  still too crude to yield anything more than imprecise boundary

  conditions that set limits only on the most extreme possibilities.

  Based on the proportions from the wings of other Cretaceous

  pterodactyls, the best estimate of the wingspan for the Big Bend

  dragon remains, in my opinion, the original fifty feet plus.

  Cretaceous pterodactyls from North America are notable not

  only for their size but for their flamboyant head crests as well.

  Pte
ranodon ("wing without teeth"—a reference to the toothless

  beak), Professor Marsh's big Kansas specimen, had a long, narrow,

  bony prong sticking out rearward from the top of its skull. What

  was the function of this extraordinary cranial ornament? Some have

  suggested this prong was a sort of rudder; others that it was a bony

  banner for display and intimidation. Closely related species that

  are very similar in body outline have little or no crest, so this

  problem is complicated. And no bird, living or extinct, possesses

  anything even remotely similar to Pteranodon s headgear.

  On the subject of pterodactyls, two questions are enjoying

  considerable debate: their warm-bloodedness and their relation to

  the dinosaurs. Professor Seeley summed up the nineteenth-cen-

  tury view: If pterodactyls flapped actively during flight, the heat

  generated by their muscles would have warmed their bodies to

  temperatures higher than that of the air. Seeley was almost cer-

  tainly correct (he usually was).

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  Recently developed measuring devices such as those sensitive

  in the infrared and ultra-violet allow zoologists to measure heat

  production and body temperature in all sorts of creatures engaged

  in various exercise. The various heat detectors and oxygen ana-

  lyzers placed on creatures of small size have yielded startling re-

  sults. Nineteenth-century zoology reckoned "warm-bloodedness"

  as the highest level of adaptation, reserved for the top rungs of

  Scala Naturae. Birds and mammals were clearly warm-blooded,

  snakes and insects clearly weren't. But this view was wrong, as the

  delicate apparatus of the late twentieth century reveals. Hawk-

  moths are powerful, nocturnal flying insects whose torsos are cov-

  ered with dense, hairlike scales. Elegant experiments show that

  hawkmoths heat themselves with their own flight muscles. Before

  they begin their mighty flights, hawkmoths send shivers of con-

  traction through their powerful flight muscles, generating waves

  of body heat. After the moth has raised its temperature above that

  of the air, it takes off—a warm-blooded, fur-covered flier. As long

  as it keeps flying, the hawkmoth keeps its body temperature high

  through the heat of its own movements. Powered flight requires a