Robert T Bakker Read online

  148 I THE HABITAT OF THE DINOSAURS

  considerable area. In other words, the fingers supporting the web

  would have to be long and spread out. Present-day ducks are ef-

  fective paddlers—with their hind legs, of course—and their hind

  toes are exceptionally long and widespread, so that the paddling

  web is relatively huge compared to the bird's body size. Beavers

  are among the best of modern mammalian web-propelled pad-

  dlers, and their toes feature a similar wide-spreading arrangement.

  Otters, muskrats, and bullfrogs follow the same rule. But duckbill

  dinosaurs don't. The forepaws of the wide-billed Edmontosaurus or

  of the crested Parasaurolophus are the exact opposite of what could

  be expected in a specialized paddle. Those duckbills' front toe bones

  are short and the three main fingers are carried closely together

  with hardly any spread at all to the overall hand pattern. A very

  strange arrangement indeed if these dinosaurs were as fond of

  swimming as orthodoxy says.

  So the duckbill's forepaw was manifestly inadequate for effec-

  tive propulsion in water; but the orthodox theory maintains a sec-

  ond line of defense, the hind feet. Duckbills concentrated almost

  all their limb power in their huge hind legs, which were twice the

  thickness of their forelimbs. If evolution wanted to design a swim-

  ming duckbill, it would be logical to make the hind paw, not the

  forepaw, the main underwater propulsive organ. Therefore the toes

  of the hind feet should be long and spreading. But, once again,

  they are not. The duckbills' hind toes are among the very shortest

  ever evolved in the Dinosauria—much shorter, for example, than

  those of the meat-eating tyrannosaurs or the plant-eating horned

  dinosaurs.

  Duckbills trace their lineage back to a gazelle-dinosaur, a small,

  long-legged, fast runner like Dryosaurus from Como. Dryosaurus

  possessed relatively longer toes than its duckbill descendants and

  thus might have paddled better. But according to the orthodox

  theory, Dryosaurus was strictly terrestrial in its habits, a confirmed

  landlubber, while the shorter-toed duckbills were supposedly

  committed to a watery life style. This paradox demands further

  scrutiny. Evolutionary processes are supposed to alter adaptations

  so that their possessors become better fitted to their new environ-

  ments. But duckbills became progressively shorter-toed and

  therefore progressively worse adapted for paddling, the very habit

  they were supposedly evolving toward.

  The argument for the swimming duckbill presents a third, ap-

  THE CASE OF THE DUCKBILL'S HAND I 149

  Duckbill ancestors had long toes.

  Dryosaurus and Laosaurus (shown

  here) had much longer hind toes

  than did the more advanced

  duckbills.

  parently very strong point—the flattened tail. Crocodiles and Nile

  monitor lizards are excellent swimmers, which employ the sculling

  strokes of their deep, flat-sided tails to propel themselves through

  tropical lakes and rivers. Deep, flat-sided tails are the characteris-

  tic locomotor equipment of other reptilian swimmers, too—the sea

  snakes of Indonesia and the extinct giant sea lizards of the Creta-

  ceous. When the first complete duckbill skeletons turned up in the

  1880s, one striking peculiarity was immediately noticed: the un-

  precedented depth of the tail vertebrae. The bony spikes rising

  150 I THE HABITAT OF THE DINOSAURS

  from the upper vertebral bodies were of great height, and the lower

  vertebral spines, called chevrons, were nearly as long. And so it

  was proved: duckbills swam with sculling movements of their deep

  caudal organ. And nearly all the textbooks repeat this conclusion

  today, with complete assurance. But this hypothesis is rendered

  highly dubious by every important detail of the anatomy.

  First, there's the problem of muscle power to support the al-

  leged swimming stroke. Swinging the flat-sided tail back and forth

  against the water's resistance would require great muscular power.

  Strong tail-scullers today have thick muscles at the base of the tail

  and great spines of bone, called transverse processes, beneath them,

  sticking out sideways from the vertebral bodies to provide strong

  sites for the attachment of the muscles. Wide transverse vertebral

  processes are found in some dinosaurs—the armored ankylosaurs

  possessed outstandingly wide tail bases and must have had great

  power in the sideways swing of their tails. As the ankylosaur's tail

  ended in a bony war club, it's not surprising that the muscles at

  the base of that tail were provided with strong attachments. The

  duckbill's ancestors were also fairly strong in the rump; the Dry-

  osaurus clan show good-sized transverse processes on the first ten

  tail vertebrae, counting from the hips back. Since evolution sup-

  posedly made duckbills better swimmers than their ancestors, we

  should expect to find duckbills outfitted with very wide transverse

  bony spines. We find no such thing. Edmontosaurus, the wide-

  mouthed duckbill, had a tail base of only moderate width, nar-

  rower relative to its body size than that of the ancestral dryosaurs.

  It would have required a massively muscled rump to send Edmon-

  tosaurus sculling through the Cretaceous bayous, and its modest

  tail base was manifestly inadequate for that.

  There are even more serious problems. The most specialized

  duckbills were the hollow-crested group, Corythosaurus, Parasau-

  rolophus, and their kin. They are inevitably portrayed as water-

  lovers with prodigious natatory prowess. But their transverse tail

  spines were absolutely puny—short, thin, weakly braced prongs of

  bone, which could have supported only an atrophied set of tail-

  flexing muscles. Thus hollow-crested duckbills, allegedly among the

  strongest swimmers in all dinosaurdom, were actually weak-rumped,

  puny-tailed creatures incapable of the powerful contractions re-

  quired of a fast-swimming sculler.

  THE CASE OF THE DUCKBILL'S HAND I 151

  Further problems concerning the caudal configurations are

  raised by the geometry of the upper tail spines. The duckbill's up-

  per spines are indeed very long. The tails of living crocodilians also

  feature long spines. But the geometrical arrangement is totally dif-

  ferent. Crocodile tail spines rise almost straight up, from the seg-

  ments of the backbone. So do those of the Nile monitor lizards.

  Most land-living lizards—the iguanas, for example—also possess tall

  tail spines, but in them the bony spikes slant strongly backward.

  The difference between vertical and slanted spines is explained by

  Why duckbills couldn't swim well. A good tail swimmer—like a modern

  crocodile—has a special arrangement of bony prongs in the backbone. Wide

  prongs that stick sideways attach to the powerful tail muscles. And tall

  vertical prongs give sinuous flexibility. Duckbill dinosaur tails were wrong on

  both counts. Their sideways prongs (transverse processes) were too short to

  support
big muscles. And the upper prongs (neural spines) were too short

  and slanted too far to the rear.

  152 | THE HABITAT OF THE DINOSAURS

  ligament action. A layer of tough ligament runs along the midline

  of the tail, and each spine is embedded into it. When the spines

  slant backward, this ligament is stretched when the tail is bent side-

  ways. Such stretching impels the tail back in the direction from

  which it came, so the land lizard can flex its tail back and forth

  quickly as it runs. Underwater, much slower, stronger flexing would

  be required, and the elastic-rebound effect produced by slanted

  spines would be useless. So specialized tails of swimmers have

  vertical spines.

  Duckbills were supposedly croc-style swimmers, moving by

  strong, easy, side-to-side flexures of their tail. Therefore, the op-

  timal design would feature vertical tail spines. But duckbill spines

  all slanted strongly backward, exactly as in land-living lizards, not

  in swimmers.

  Another problem in the duckbill's swimming equipment lies

  in the profile of the tail. The deepest part of the croc's tail is close

  to the end, because the end swings through a wider arc than does

  the base in moving side to side. Thus the tail is deepest where it

  can do the most good in pushing against the water. All powerful

  tail-scullers have such deep tail ends. But duckbill tails were deep-

  est at the hips and become progressively narrower from top-to-

  bottom toward the tip—another caudal feature nearly totally

  maladapted for its alleged primary function.

  An argument very eloquently expressed in 1964 by John Os-

  trom of Yale administers the coup de grace to the theory that

  duckbills swam. Any sort of tail-propelled swimming requires a

  smooth ripple of tail flexure from the hip out to the tip of the tail,

  a sort of muscular sine wave that pushes against the water's resis-

  tance to propel the animal forward. Even with the handicap of a

  weak rump and their maladapted shape, duckbills could have swum

  at least at slow speed if they could undulate their tails. The only

  anatomical feature that would have entirely prevented a dinosaur

  from swimming would be a tail corset, a stiff latticework of bone

  which would hold the entire tail assembly together as one stiff im-

  mobile mass. Tail corsets evolved in a wide range of dinosaurs,

  including some meat-eaters, some plant-eaters, and the long-tailed

  flying dinosaurs (pterosaurs). No modern reptile has a tail cor-

  set—all the lizards, turtles, and crocs can wiggle their tails freely,

  and even the weak-tailed lizards (desert horned toads, for exam-

  THE CASE OF THE DUCKBILL'S HAND

  153

  pie) can employ their caudal undulations to swim when the animal

  is forced to. But when the skeletons of duckbill tails were found,

  their single most startling feature was a basketwork of long, stiff

  bony rods crisscrossing over the backbone from the mid-chest all

  the way to near the tail's end. A perfect tail corset. Each rod con-

  sisted of dense bone up to half an inch thick and was attached at

  one end to the bones of the vertebral column by a short stiff lig-

  ament. Dryosaurs had a tail corset, too, as did horned dinosaurs,

  but the ultimate in caudal basketwork was developed in the duck-

  bills. *

  The duckbill's tail corset evolved for an obvious mechanical

  purpose: to keep its backbone stiff and immobile from a point just

  behind its shoulders all the way down to the hindmost tail section.

  Even the most devout believers in swimming duckbills are forced

  to admit that this bony latticework would make for an unusually

  unsupple spine, the very reverse of what is necessary for swim-

  ming with smooth, horizontal undulations.

  The supposedly definitive monograph on duckbills came out

  in 1942. Its two authors (one was the senior professor of paleon-

  tology at Yale) had to engage in quite a twisted form of logic to

  explain away the problem of the duckbill's stiff backside. They ad-

  mitted the bony system of rods must have evolved to maintain the

  backbone rigid for perambulations on land when the duckbills chose

  to walk about on terra firma. But perhaps, the authors argued, the

  tendons were a little loose so that a small degree of side-to-side

  movement was possible in the tail. But they ignored a critical

  problem. The duckbill's ancestors had been land livers, with mod-

  erately strong tail corsets, and the duckbills themselves increased

  the stiffness of the corset. The monographers of '42 failed to ex-

  plain why duckbills would evolve in the wrong direction—why the

  duckbill family had stiffer, not more supple, tails than their ances-

  tors.

  The sum of evolutionary evidence is thoroughly damning. In

  nearly every modification of the evolutionary process made in the

  duckbills as they developed from their dryosaur ancestors, the

  duckbills suffered a diminution of their swimming potential. Their

  fore- and hind paws became shorter and more compact, not longer

  and more widely spread. Their tails got weaker and stiffer. Far from

  being the best, the duckbills must have been the clumsiest and

  154 | THE HABITAT OF THE DINOSAURS

  Body-tail corset

  of a duckbill

  (Corytbosaurus)

  slowest swimmers in all the Dinosauria. If pressed, they probably

  could paddle slowly from one riverbank to another. The central

  theme of their bodily evolution was indeed specialized—orthodox

  theory was right on that point—but the direction of specialization

  was landward. These dinosaurs were specialized for a totally ter-

  restrial existence.

  Every so often some paleontologists attempt placing some other

  major dinosaur group in the water. A young Canadian would have

  Alberta horned dinosaurs wading through the sluggish backwaters

  of the Judith Delta. But his evidence derived from the dubious

  notion that the horned dinosaurs spent most of their lives in the

  water because their fossils are found buried in river-channel sand-

  stone. American buffalo often are found buried in river sands where

  their bodies came to rest after a flood, yet the buffalo is hardly an

  THE CASE OF THE DUCKBILL'S HAND

  155

  aquatic creature. One quick way to calculate how well a dinosaur

  would cope with swampy terrain is to calculate the area of its hind

  foot available to support the downward thrust of its hind leg. Any-

  one who has tramped around as many bogs and swamps as I have

  knows that feet get stuck not when you stand still, but when you

  step too forcefully and drive your leg down into the muck. The

  faster you walk, the more downward thrust is applied to the sole

  of the foot. Hence to move speedily over mud or soft earth, de-

  vices such as snowshoes must be used to expand the foot's area.

  Hippos follow this pattern: they have wide-spreading toes relative

  to the power of their legs, a contrast to the small, short-toed feet

  of the rhino. Since all dinosaurs had stronger hind limbs than fore,

  the
largest thrust would be exerted by their thigh muscles. So the

  thickness of the thigh bone (femur) works as a useful gauge of the

  Long toes in a hippo (left) and

  short toes in a brontosaur (right)

  156

  THE HABITAT OF THE DINOSAURS

  force applied to the sole of the feet. From fossil footprints, the

  area of a dinosaur's foot can be calculated and then compared with

  the cross section of the femur.

  This exercise in quantitative paleopodiatry produces dis-

  tinctly counterorthodox conclusions. All the popular books list

  - brontosaurs and duckbills at the top of the list in the preference

  for swamps. But brontosaurs and duckbills had among the small-

  est feet in area relative to the size of their thigh. If these giants

  had tried to spend their lives paddling around marshy terrain, they'd

  have found themselves stuck in the mud with genuinely maladap-

  tive frequency.

  Stegosaurs and ankylosaurs were also compact of foot. But the

  horned dinosaurs had much bigger feet per pound of thrust from

  the thigh. A few dinosaurs were especially large-footed—some lit-

  tle horned dinosaurs, the primitive anchisaurs (brontosaur ances-

  tors), the dryosaurs, and most of the meat-eaters, both large and

  small. Strangely enough, it's these dryosaurs and meat-eaters that

  are supposedly least adapted for soft swampy soils according to

  orthodox dinosaur ecology. But like so much else in traditional

  dinolore, the standard story about feet and mud is not accurate.

  Museum exhibits teach that brontosaurs and duckbills escaped their

  predatory enemies by wading out into the marshes where meat-

  eaters feared to tread. But if an allosaur pursued a brontosaur or

  a tyrannosaur pursued a duckbill, it would be the ponderous pads

  of the plant-eaters that would mire first into the mud to hold their

  hapless owners fast as the killer descended.

  After all this calculation of tail mechanics and foot areas has

  been done, that duckbill mummy's hand, that webbed forefoot

  raised forever skyward in its fourth-floor glass case at the Ameri-

  can Museum of Natural History still requires an explanation. If it

  was not for swimming, then what was it for? A dead camel I ob-

  served in the Transvaal might solve this mystery. While I was in