Robert T Bakker Read online

  joint, but not nearly to the degree found in Diplodocus.

  In living species, the position of the head relative to the neck

  is often determined by the animal's feeding habits. Hence the hor-

  izontal head and the vertical neck in Diplodocus imply that its neck

  was held nearly vertically during feeding. Since the neck is very

  long, Diplodocus must have been feeding at very high levels—twenty

  or thirty feet above the ground. Not many clams are found living

  at such heights. More likely the Diplodocus searched the upper

  reaches of Jurassic trees for select vegetarian morsels. With its

  sharply tapered snout, Diplodocus could probe deeply in among the

  branches, choosing its menu with more care and delicacy than the

  big-toothed Camarasaurus or Brachiosaurus could.

  Diplodocus's head—neck anatomy simply contradicts those tra-

  ditional restorations of the beast portrayed as feeding exclusively

  on ground level with its long neck outstretched. Why evolve a

  twenty-foot neck at all if feeding was done exclusively on the

  ground? Diplodocus had short front legs, so a six-foot neck would

  have sufficed quite nicely for ground feeding. Ostriches are long-

  necked ground feeders, but they have very different problems—

  they are very long-legged and require their long neck just to reach

  the ground.

  The most troublesome part of a Diplodocus's head is not its

  GIZZARD STONES AND BRONTOSAUR MENUS I 139

  Diplodocus nostrils were in a whale-type position—on the forehead between

  the eyes.

  teeth but its whalelike nostrils. Most air-breathing vertebrates have

  their nostrils at the tip of the snout. Air is drawn in through the

  nostrils, passes through a tube in the snout, and is then drawn

  downward through a hole in the roof of the mouth into the wind-

  pipe. The windpipe lies just behind the base of the tongue. But

  whales do it differently. Whale nostrils—their blowholes—are lo-

  cated way back on the skull right above the eyes. When a whale

  exhales after a deep dive, a geyser of humid air is blown nearly

  directly upward from its forehead. (Sperm whales have a long tube

  running through their fleshy snout from the blowhole in the skull,

  so, rather exceptionally, sperm whales blow from the front of the

  snout.) Nostrils in the whale position seem an obvious advantage

  for a swimming air-breather. The typical whale can inhale and ex-

  hale from its blowhole without danger of ramming water into its

  nostrils. And nostrils at the tip of the snout would be more vul-

  nerable to the rush of water caused when the head plunges back

  below the ocean's surface.

  Diplodocus had nostrils in the whale position—just in front of

  and above the eyes. If you are inclined to believe the water-living

  theory, the interpretation of Diplodocus's nostrils is obvious: The

  140 i THE HABITAT OF THE DINOSAURS

  Did Diplodocus have an elephant-style trunk? Modern

  elephants have bony nostrils located in the forehead position.

  beast used its skull as a combination snorkel-periscope to simul-

  taneously breathe and look around while only the forehead was

  exposed above the level of the water.

  An alternative explanation is however possible. There is one

  type of forehead structure found among living species that matches

  the Diplodocus's—the foreheads of mammals with trunks. Ele-

  phants have nostrils located exactly in the Diplodocus position, be-

  tween the eyes on the forehead. Tapirs—short-legged relatives of

  horses—possess nostrils located halfway between the elephant po-

  sition and the usual mammal location at the end of the snout. Ta-

  pirs have trunks of moderate length. A trunk is actually a highly

  GIZZARD STONES AND BRONTOSAUR MENUS | 141

  modified set of upper lip muscles that surround the fleshy nostrils

  and wrap around to form a mobile muscular tube. Usually the fleshy

  nostril—the hole in the skin through which the breath passes—is

  located in the flesh that more or less directly covers the bony nos-

  tril hole in the skull. But in a trunk the fleshy nostril is carried at

  the end of the mobile tube. In fossil mammal skulls, a trunk can

  be hypothesized if the bony nostril is located in the elephant or

  tapir position, and the skull bones around the nostril show attach-

  ment sites for the modified lip muscles.

  I find the similarity between a Diplodocus's forehead and an

  elephant's thoroughly unsettling. Could Diplodocus have been a di-

  nosaur equipped with a proboscis? A horrendously heterodox

  thought, but not a new one. The possibility of trunked dinosaurs

  has been raised in paleontological journals on and off for half a

  century. There are all sorts of evolutionary problems generated by

  this theory. First of all, to produce a trunk, evolution requires a

  start with a set of muscular lips. Nearly all mammals possess a

  complex set of lip and face muscles, so evolving a trunk from any

  given mammal ancestor poses no great difficulty. But reptiles pos-

  sess hardly any lips at all. Lizards have thin muscular bands run-

  ning along the inner edges of their lips—just enough muscular tissue

  to flare the lips a bit to bare the teeth. But lizards don't have enough

  lip muscle to pucker, suck, flare the nostrils, or wiggle the nose.

  Crocs are even more lipless. The muscular lip band found in liz-

  ards is gone entirely in crocs, which have only a thin, scaly layer

  of skin over the gums. These thin croc lips are so tightly con-

  nected to the jaw and skull bones that they can't move at all. The

  thin band of the lizard lip hangs down enough to hide the teeth

  when the mouth is closed. But the croc lips hide nothing; its up-

  per teeth are visible sticking down out of the gums even when its

  mouth is closed. Crocs have achieved the ultimate tight-lipped

  condition. The croc jawbone curves upward at the rear, which ac-

  counts for a smile the animal seems to have frozen on its face. In

  point of fact, crocs can't smile at all.

  What sort of lips did dinosaurs have? Primitive brontosaur

  relatives, like Massospondylus, possessed bony gums just as mod-

  ern lizards do. On the fossil gumline along the outer edge of the

  upper and lower jaw there is a gently beveled edge which must

  have been the attachment site for thin, muscular, lizard-style lips.

  142 | THE HABITAT OF THE DINOSAURS

  Crocodile lips. Croc facial skin is thin and tightly fixed to the skull bones, so

  there are no movable lips along the gum line. Tooth shape shown at right.

  Lips require blood for nutrition and nerve fibers to carry sensory

  information to the brain. Massopondylus shows a series of holes in

  the jawbones precisely where the lips would lie in life. Through

  these holes passed the requisite blood vessels and nerve tracts. An

  identical pattern of holes can be found in the jawbones of living

  lizard species. So Massospondylus, the brontosaur uncle, was

  equipped with a little bit of lip, and primitive dinosaurs of the

  Triassic Period were all similarly lizard-lipped. The predatory di-


  nosaurs, Allosaurus, Ceratosaurus, and the tyrannosaurs, retained this

  lizard-lipped condition into the later periods. Therefore Tyranno-

  saurus can be restored accurately with a sneer on its face or in the

  act of baring its teeth.

  It is not totally impossible that evolution could convert the

  lips of Massospondylus into a big complex system of elephantlike

  face muscles, complete with proboscis. If Diplodocus really walked

  around with a trunk hanging from its forehead, some evidence of

  big proboscis muscles attaching to the skull bones near the edges

  of the bony nostril would have to be found. I can't find any such

  marks. But the Diplodocus's lips were definitely different from those

  of lizards—the gum lines along its jawbones were not beveled, and

  the holes for blood vessels and nerves did not make an evenly

  GIZZARD STONES AND BRONTOSAUR MENUS | 143

  spaced row like the one in lizards. Diplodocus's lips were different

  from those of crocs, too. In the tight-lipped crocs, the skull bone

  beneath the thin scaly lip tissue is pitted and grooved so that the

  horny skin can attach very firmly to this roughened bone surface.

  Diplodocus's jawbones were quite smooth compared to crocs'.

  It's very unclear how Diplodocus's lips were attached to its skull,

  but the possibility of a proboscis must be explored by more ana-

  tomical research. Alternative explanations for the locations of Di-

  plodocus's nostrils should also be explored—were they perhaps

  adaptations for tooting and honking? Primitive dinosaurs close to

  the brontosaurs, such as Massospondylus, may have snorted. The

  bony nostril hole is quite capacious in these early species and must

  have housed a series of pockets and compartments structured from

  skin, cartilage, and nasal lining. Compartments of soft, nonbony

  tissue in horses' skulls amplify their snorts and whinnies. Perhaps

  Massospondylus's nostrils performed the same functions. Stout-

  toothed brontosaurs like Camarasaurus and Bracbiosaurus had truly

  gigantic bony nostrils, so large that the eye sockets appear small

  by comparison. The bony nostril hole on each side of the skull is

  so enlarged in these species that only a tiny strip of bone separates

  the right from the left orifice. In life, these gigantic apertures were

  filled by some form of enlarged nasal device. The nasal organ was

  sufficiently large to spread over the snout bones, because the mark

  left by the soft-tissue nose can be seen on the top surface of the

  fossil snout. What important biological function required such a

  huge nose? The Camarasaurus's bony nostril vaguely resembles a

  Tyrannosaur lips.

  Tyrannosaurus, like

  Massospondylus and

  other primitive

  dinosaurs, had a lizard-

  style lip band along the

  gum line. A row of

  bony lip holes in the

  skull and jaws shows

  how blood vessels and

  nerves reached the

  movable lips.

  144 | THE HABITAT OF THE DINOSAURS

  tapir's, and therefore the possibility of a short proboscis cannot be

  dismissed. Or the nostril hole may have housed resonating cham-

  bers to provide its owner's voice with a rich and varied timbre.

  If brontosaurs in general possessed nasal adaptations for bel-

  lowing out Jurassic songs, perhaps, just perhaps, Diplodocus's fore-

  head nostrils were part of its nasal symphony. Diplodocus had small

  nostrils but probably evolved from an ancestor with gigantic bony

  nostrils like those of Camarasaurus. If Diplodocus's ancestors had

  been nose-honkers, roofing over the narial tissue would have al-

  tered the tone—probably making it brassier.

  Brontosaur faces and noses are still full of mystery. Right now,

  fossil tongues are the exciting topic in paleontology. The tongue

  itself doesn't fossilize, but the tongue bones in the throat do—and

  tongue muscles leave their marks where they attach to skull and

  jaws. But too few researchers are studying lips and their evolu-

  tion. Someday someone will win his or her place in the history of

  science by solving the mystery of brontosaur noses and lips. When

  I'm asked by students what they should study, I always reply, "Think

  lips."

  Diplodocus nostrils as

  nose flutes. Primitive

  brontosaurs—like

  Camarasaurus and

  Bracbiosaurus—had

  huge bony nostrils that

  must have been

  covered with a fleshy

  chamber. The big

  chamber may have

  been used to amplify

  sound. In Diplodocus

  the nasal chamber is

  roofed over by the

  snout bones, so that

  the sound produced

  would have been

  brassier than that of a

  camarasaur or

  brachiosaur.

  GIZZARD STONES AND BRONTOSAUR MENUS | 145

  7

  THE CASE OF THE

  DUCKBILL'S HAND

  On the fourth floor of the American Museum of Natural His-

  tory in New York, in a square glass case, stands the nearly

  complete, mummified carcass of a twenty-foot duckbill dinosaur.

  That mummy is famous worldwide for its hands.

  In the early days of paleontology, the scientists of Europe and

  America expected that if dinosaur skin impressions were ever found,

  they would reveal a scaly hide. Up to 1900 only a few small patches

  of skin marks had been recovered from European dinosaurs and

  none from American. The Late Cretaceous delta beds of the

  American West changed all that. Expeditions from the American

  Museum to the Red Deer River in Alberta uncovered complete

  duckbill skeletons, including enormous patches of skin impressed

  in the sandstone around the ribcage, tail, and neck. The skin's

  substance itself was of course not preserved—it had rotted away

  after the duckbill had been entombed by a sudden influx of sand.

  But sand and mud had infiltrated the duckbill's body cavities while

  the dried hide still separated the animal's insides from the sur-

  rounding sediment. Consequently, when the sandstone was care-

  fully chipped away, the surface of the vanished skin acted as a

  separation layer, so the stone faithfully recorded the living skin's

  texture. The American Museum's technicians—probably the best

  in the world at the time—erected twenty-foot slabs of sandstone

  in their exhibit hall, displaying the Alberta duckbill skeletons as

  146 | THE HABITAT OF THE DINOSAURS

  Web-propelled swimmers,

  like modern ducks, had

  long, widely spread toes.

  Duckbills supposedly

  paddled with their webbed

  feet. But both forepaws and

  hind paws had very short

  toes that did not spread

  much, not a good design for

  fast swimming.

  they had lain, half-embedded in rock, still partially clothed in their

  skin texture.

  Even more spectacular mummies subsequently came from

  Wyoming's Lance Creek beds. The Alberta skeletons lay on their

  sides,
their skin impressions flattened by the overlying rock bod-

  ies—producing a two-dimensional appearance. The Wyoming

  mummies however were nearly entire bodies, preserved lying on

  their backs, their chests expanded as if in a last gasp for breath,

  both fore and hind feet extended outward in an agonized pose.

  Impressions of skin covered each carcass on all sides. So lifelike

  do these three-dimensional mummies look, it is easily possible to

  imagine driving across a dried-up lake and happening upon just

  such a carcass, victim of a drought, sprawled with its collapsed belly

  pointing upward, legs contorted into unnatural angles by the con-

  traction of sun-dried skin. Something about these contortions of

  death, so eloquently preserved in sand, drives home the message:

  This twenty-foot carcass was once alive, with full, pulsating mus-

  cles filling out the now cadaverous torso.

  Duckbill dinosaur skulls and skeletons had entered the annals

  of science during the 1880s. The broad, ducklike muzzles sug-

  gested in a vague way some sort of mud-grubbing habits. But when

  the hands of the recently arrived three-dimensional mummy were

  finally cleaned, they caused a sensation. The skin impressions con-

  tinued down the wrist, and between the duckbill's fingers. The

  conclusion was obvious—the duckbill's feet were webbed! The

  concept of aquatic duckbills, up till then an ill-defined theory,

  crystallized into a solid scientific "fact"—duckbills had webbed feet,

  duckbills swam. From that moment on, nearly every popular and

  scientific account of duckbill dinosaurs portrayed them paddling

  through lakes and rivers. The exhibits in the New York Museum

  depicted crested duckbills rushing into the water, with huge wad-

  dling strides; the caption read: "Escape to the Swamps." And once

  the aquatic theory became "fact," all the quirks of the duckbill's

  anatomy were forced into supporting the notion of an aquatic mode

  of life. The hollow crests of some duckbills were even hypothe-

  sized as air reservoirs adapted for prolonged diving.

  A more careful consideration of the duckbill mummy's webbed

  paddle raises important heretical doubts about its aquatic role. If

  three-ton duckbills paddled at fair speed through the swamp waters

  of their Cretaceous delta home, they would require a paddle of