Robert T Bakker

by The Dinosaur Heresies (pdf)

  swered, it will provide unique insights into how it lived, what ene-

  mies it feared. This mangled carcass can in fact help test the widely

  believed theory that brontosaurs were swamp dwellers, sloshing

  around lakes and rivers up to their armpits to keep their imprac-

  ticable bulk buoyed up by the tepid waters. If that theory is true,

  then this Camarasaurus very likely died in its favorite watery hab-

  itat. Can that idea be tested? Very easily. If the body sank in an

  aqueous grave, it should be resting on the type of sediment laid

  down on lake or stream bottoms.

  Along this limestone outcrop where the bones are eroding out,

  there is only this one carcass—scattered vertebrae from the neck

  THE CASE OF THE BRONTOSAURUS: FINDING THE BODY

  105

  How sediment was

  laid down at Como

  and back, a shoulder blade, a thigh bone—all the right size to fit

  together and make one skeleton. The bones aren't jumbled on top

  of each other. They lie close together in a layer one bone deep.

  Clearly this body fell apart, ligaments rotted, knee detached from

  thigh, neck vertebrae separated from one another. Such rotting of

  the ligaments could have happened underwater while the body lay

  in the muck. Crayfish, turtles, and other bottom scavengers would

  have crawled over it, tugging and biting at every shred of flesh. Or

  it could have happened on land, where dryshod predators could have

  pulled the meat and gristle apart. Which scenario is correct?

  The surrounding rock of the bone layer is a dark gray mud-

  stone containing little streaks of sand grains here and there. No

  distinct layers, though; no fine horizontal bedding. And that is a

  clue. Mud settling through standing water—a pond or swamp—

  usually deposits clear-cut layers, one piled on top of the other, be-

  cause the flow of mud particles is almost never constant. Usually,

  the flow of mud into the lake varies with rainfall and flooding. A

  spring flood sweeps coarser sand into the pond, the sand sinks, a

  106

  THE HABITAT OF THE DINOSAURS

  layer is formed. Gentle showers wash fine mud into the pond, the

  mud sinks on top of the sand, another layer. Such layers of mud

  undisturbed often form delicate sheets, because the fine clay par-

  ticles which compose them are in the shape of microscopic plates

  that lie flat on top of each other. The lack of layering thus suggests

  this body didn't lie on a deep lake bottom. Very deep lakes usu-

  ally possess bottom mud with very clearly defined layering.

  Protruding from under the bones is the limestone of the Cam

  Bench. Why does this layer stick out from the eroded bank? Ob-

  viously because it's harder than the bone-bearing layer above it.

  But why is the lower layer harder? Because it's a limestone—and

  limestone resists erosion in this dry Wyoming climate. But this is

  not an ordinary limestone. Most limestones form underwater, when

  lime (calcium carbonate) precipitates out of solution. This lime-

  stone is made up of little balls, from pinhead size to golfball size,

  packed together, jammed onto each other.

  A closer look at these broken lime balls reveals that some have

  a tiny grain of sand at the core, others a few mud streaks. Such

  lime balls can form in gently agitated warm water—the action of

  the waves rocks small particles as they clothe themselves with layer

  after layer of lime. But these aqueous lime balls, called ooids ("oh-

  oyds"), are usually all of nearly one size, not at all like these in the

  Cam Bench, where pin-sized balls lie adjacent to others a hundred

  times bigger. Furthermore, ooids usually show internal layering,

  like an onion. These lime balls below the skeleton don't. Instead,

  the Cam Bench lime balls look like the ones called kunkar that

  grow in well-drained soil today in tropical India. So the camara-

  saur could have died on dry land.

  Now, do such irregular lime balls as these grow anywhere to-

  day—and if they do, in what kind of habitat? An answer to that

  question might tell us where this one dinosaur body lays, and

  therefore where it lived and died. Soil scientists in Australia and

  India have found exactly the right thing. In tropical soils where

  the particles are well drained for most of the year, a trench dug

  into the soil layers will reveal a zone of lime balls a foot or so

  beneath the surface. Lime in solution washes down from the soil's

  surface during the rains. As the water dribbles and oozes down-

  ward, some lime drops out of solution and tiny lime pellets form,

  growing bigger each year. In many tropical landscapes these lime

  THE CASE OF THE BRONTOSAURUS: FINDING THE BODY I 107

  Death of a camarasaur. Adult camarasaurs were too big to fear most

  predators—the camarasaur's fifteen-ton bulk was immune to attack by the

  average one-ton Allosaurus, But when sickness weakened their resistance,

  even a full-grown camarasaur could fall victim to the steak-knife teeth of the

  dinosaurian hunters.

  balls lack internal layering—just like the ones under the fossil di-

  nosaur. Aussie soil scientists call this type of lime ball "kunkar."

  If the lime balls under the skeleton are truly kunkar, that would

  be grounds for considerable excitement. Kunkar nodules would

  prove that this soil was originally not swampy and wet, because

  swampy soil water is usually acid and dissolves lime balls as quickly

  108 | THE HABITAT OF THE DINOSAURS

  as they form. In such acid soil a conspicuous kunkar layer never

  forms. If brontosaurs died on kunkar-growing soil, it means they

  probably lived on dry, firm ground, and not in swamps at all.

  Layers of lime balls growing today in Indian soils have one

  characteristic signature: the balls get bigger toward the top of the

  layers, because the top balls receive more lime from the water

  THE CASE OF THE BRONTOSAURUS: FINDING THE BODY I 109

  percolating downward. A trench hacked into this limestone out-

  crop exposes unweathered rock, and the balls do indeed get big-

  ger toward the top! It certainly looks as if this particular brontosaur

  died on a land surface, just above a layer of irregular-sized lime

  balls growing in the soil.

  Could we prove, however, that this was a land death? What's

  on trial here is not a murder suspect, but a suspect theory. Tra-

  ditional theory maintains that the big dinosaurs were water crea-

  tures—and old theories are tough antagonists in court. The scientific

  establishment tends to believe that old, accepted views are correct

  unless shown to be wrong beyond any reasonable doubt.

  Here at Como we need the equivalent of the spent bullet,

  lodged in the carcass, that can be securely traced to the murder

  weapon. We need to find one more independent piece of evi-

  dence that this multi-ton giant met its end on land. Further inves-

  tigation around the eroding carcass reveals that some of the bones

  are scarred by deep, knifelike wounds. These could be teeth marks

  of the predator that killed the brontosaur or of the scavengers t
hat

  stripped the body after death. In the dust a gleaming piece of tooth

  enamel catches the sun: a tooth, four inches long, pointed, sharp-

  edged, with sawlike serrations along front and back. Not the Ca-

  marasaurus's tooth—the victim was a vegetarian. The tooth is from

  a big Ceratosaurus, a bipedal predator.

  The Ceratosaurus tooth is the spent bullet. This predator's tooth

  clearly broke off as the flesh-eater bit into the brontosaur. At the

  base of the tooth, where the root should be, is a deep pit where

  the root had been dissolved by the Ceratosaurus gums. We hu-

  mans think of tooth loss as a tragedy, because once gone, our adult

  molars leave nothing but a hole in our jaw. But Ceratosaurus and

  all the other dinosaurs had an endless supply of teeth forming at

  each socket. As a new tooth grew in the socket, its pointed tip

  pushed out the old tooth. The new tooth grew upward as its root

  grew longer—the old tooth's root was dissolved to make room for

  the new. An X-ray of a ceratosaur jaw reveals four or five teeth,

  all in a row from top to bottom, each growing upward, pushing

  the one ahead.

  Fractured edges around the root remnants of the ceratosaur

  tooth show that it broke off during life; the big predator was bit-

  ing into something hard enough to break the tooth off its jaw.

  110 I THE HABITAT OF THE DINOSAURS

  How new teeth grow out

  and push old teeth from

  their sockets (shown is the

  predator Ceratosaurus)

  There is another Ceratosaurus tooth, and another. All three

  are the right size to come from the same animal, and all three broke

  off during life. This is the killer—or at least a beast that bit into

  the dinosaur carcass after death. And Ceratosaurus was a land

  predator, not a swimming meat-eater like the crocodile. Ceratosau-

  rus hunted for prey on land, either killing the young and weak

  brontosaurs or searching for brontosaurs that had died of other

  causes. So broken ceratosaur teeth supply our sought-for clue. The

  case for death on land is solid.

  If a brontosaur carcass lay on a pond bottom or floated on a

  lake surface, it wouldn't attract land predators, it would attract

  crocodiles, which swarm over any available meat. Crocs shed their

  teeth just as dinosaurs did, and when crocs bite into a big carcass,

  a few teeth usually detach and stick embedded in the body. If our

  brontosaur carcass had ever been in water for a long time, we would

  THE CASE OF THE BRONTOSAURUS: FINDING THE BODY | 111

  expect to find some croc teeth with it. But in digging around the

  site for five days, not one croc tooth turns up. A few feet above

  the lime-pellet bench there is a stream deposit full of broken and

  shed crocodile teeth mixed with clamshells and turtle bones. This

  deposit clearly preserves the record of water-living predators and

  their victims, a record which is absent in the case of our Camara-

  saurus.

  The case is looking good—the vegetarian Camarasaurus died

  on land and was chewed up by a Ceratosaurus. But now a compli-

  cation. The plot thickens when the shed teeth of a second big

  predator, Allosaurus, a very different species, turn up among the

  Camarasaurus bones. And then yet another predator's teeth—this

  time a very small killer, Coelurus, only the size of a very big tur-

  key.

  A moment's reflection produces a clear solution to this case.

  In land ecosystems today, a big carcass is an enormous amount of

  protein waiting to be used by any and all predators. Whether a big

  water buffalo dies of disease or from a lion's attack, the sight and

  smell of the dead hulk will attract lions, hyenas, jackals, and vul-

  tures from a wide radius. After the biggest, most aggressive flesh-

  eaters have eaten their fill, the smaller jackals and foxes nip in to

  tear off their share. And thus one buffalo carcass gets chewed and

  pulled apart by successive crews of large and small predators.

  Only one more piece of evidence of how the Cam Bench

  brontosaur died and was preserved is necessary to complete the

  case. The chewed-apart Camarasaurus carcass had somehow to be

  covered by a layer of sediment. But the layer of rock entombing

  the skeleton is unambiguous at this point. It was deposited as a

  blanket of mud when a turbid sheet of water inundated the flood-

  plain. Floodplains are special places. They can remain dry and grow

  a rich carpet of bushes, young trees, ferns, and ground pines for

  half a year, ten years, or as much as a thousand years. It's during

  these intervals that the kunkar lime balls form in the soil below

  their surface. But floodplains get their layers of sediment when

  neighboring rivers and streams overflow. The floodwaters that have

  been rushing through river and stream channels slow down dra-

  matically when they spill over and spread across the flat lowland.

  Homeowners in Cincinnati and other floodplain cities today know

  firsthand how such sheets of floodwater can bury even large ob-

  112 | THE HABITAT OF THE DINOSAURS

  jects in mud—sometimes objects as large as a station wagon or a

  one-story house can disappear in a few days. Our Camarasaurus

  carcass, chewed and pulled apart, was gently and thoroughly cov-

  ered by just such a mud deluge. Then the floodwaters receded.

  The new layer of mud dried out. Plants began to germinate, ferns

  sprouted. A new soil surface developed atop the new blanket of

  mud, supporting the very same type of plants that had fed the cam-

  arasaur during its lifetime. Once again, kunkar nodules began to

  grow below the surface and among the camarasaur bones.

  But other arguments are possible here. The Russians have

  given a name to this type of paleontology, "taphonomy," coined

  from the Greek word for "burial" and the word for "laws." Ta-

  phonomy is when a paleontologist reconstructs the corpse's burial

  so it can reveal how and where it lived. It is important not to be

  fooled by first impressions. A fossil body's location may not be

  where the death occurred. Fossilization can be misleading. A dead

  brontosaur like the Camarasaurus lying on a floodplain probably

  means the death occurred on land. But maybe a flood washed the

  body from a river onto the land. It could happen.

  Worse yet, there's the possibility the body was dragged from

  a watery death site by the actual killer. Meat is meat and in short

  supply in most habitats. So a land predator, such as a lion, might

  pounce on a crocodile in shallow water if the croc were unwary.

  Without the least concern for whether it were messing up a po-

  tential fossil, it would drag the dead croc hundreds of yards from

  the shore to some secure spot on dry ground where the big cat

  could enjoy its scale-wrapped dinner in comfort. Large land-hunt-

  ing dinosaurs could have done the same, dragging aquatic prey into

  their terrestrial habitat.

  Taphonomy is therefore a science requiring subtlety, broad

  knowledge, and a good eye for detail. The diligent carcass sleuth

  mus
t be alert for signs that the dead body has been moved from

  water to land, or vice versa. Crocodiles are usually as hungry as

  lions and nearly as crafty. A big croc will wait in the reed-choked

  shallows for an unwary zebra to come and drink. In a minute the

  zebra disappears beneath the river's surface. And an unwary pa-

  leontologist, excavating the scene a million years later, might be

  similarly ambushed—he might conclude that the zebra was aquatic

  because he found its mangled bones buried in river sand.

  THE CASE OF THE BRONTOSAURUS: FINDING THE BODY | 113

  Rivers are moreover terrible deceivers. When modern rivers

  overflow, they wash all sorts of living and dead matter off the

  floodplain into the river channel. Consequently, sediment buries

  dead squirrels, unfortunate cows caught in the flood, lawn furni-

  ture, shopping carts, and other terrestrial debris, along with the

  fish bones and clamshells that belong there. If hundreds of dino-

  saur skeletons from a single species are found preserved in river-

  channel sediment, could it safely be concluded that the species was

  water-loving? Not at all. Big floods along the Missouri wash

  114 | THE HABITAT OF THE DINOSAURS

  hundreds of Hereford steers into the rivers, where they eventu-

  ally become buried in sandbars. Does that prove Herefords are an

  aquatic species? Dinosaurs of all kinds have been found in stream-

  and river-laid sandstones—predators like Allosaurus, armored steg-

  osaurs, and giant brontosaurs. A few years ago, a young Canadian

  paleontologist was misled into concluding that duckbill and horned

  dinosaurs were aquatic because in Alberta their skeletons are con-

  centrated within the river sandstones. But Mesozoic rivers were as

  deceptive as modern ones. Dinosaurs in rivers prove nothing con-

  clusively.

  If rivers can't be trusted, where can paleontologists turn for a

  truthful account of the brontosaur's habitat preference? Lake bot-

  toms and floodplains are the most trustworthy locales. Some fish

  and crocs do get washed and dragged up onto plains, and some

  zebras and lions do get washed or dragged into lakes. But, on av-

  erage, lake-bottom mud preserves mostly water creatures, and