Robert T Bakker

by The Dinosaur Heresies (pdf)

using its strong snout and thickly muscled torso. In the tropics sal-

  amanders are scarce, but the soil is churned up by hundreds of

  species of legless amphibians, the Apoda (Greek for "legless ones").

  Several families of frog are well-equipped excavators, digging with

  pointed snout or spadelike feet. In the Malay Archipelago, herps

  reach the summit of their locomotor evolution. Here is found the

  flying frog. Spreading the thin membranes between its long fin-

  gers and toes, the flying frog launches off a forest perch and glides

  effortlessly to another tree a hundred yards away. It's not true

  Rhacophorus—

  Flying Frog of Malaya

  MESOZOIC CLASS WARFARE: COLD-BLOODS VERSUS THE FABULOUS FURBALLS | 55

  powered flight, like the flapping progression of birds and bats, but

  the frog's powerless glide has a certain herp elegance.

  All told, in habitats from all climates, the Class Amphibia scores

  three-thousand species, just as many as the total number of non-

  flying mammals. We're not living in the Age of Mammals, we're

  living in the Age of Frogs.

  Mammal chauvinists also underestimate turtles. Compared to

  frogs and their amphibian kin, turtles don't score high in the spe-

  cies competition—only two hundred and thirty species fill the

  modern turtle clans—but turtle limbs, necks, backs, and skulls are

  true marvels of joint architecture. Most turtles can fold up every-

  thing that sticks out from the shell—neck, limbs, tail—and tuck it

  into the armored box, leaving little exposed. Several turtle species

  go even further in safeguarding their soft parts. Hinge lines have

  evolved in the top shell (the carapace) or in the bottom (the plas-

  tron) so that after it has pulled in its appendages, the turtle can

  close up the neckline and limb apertures, sealing its entire body

  into a nearly impregnable strongbox. The basic turtle shell itself is

  a most unusual structure that has evolved only through a bizarre

  bit of embryological hocus-pocus. Turtle shells have three layers:

  (1) the outer horny plates, a tough covering sheathing the bone

  beneath, like the horn-core sheaths of bison; (2) the outer bony

  plates, which lie just under the horny sheath and grow within the

  lower skin layer; and (3) the ribs, which arch around the body and

  fuse to the underside of the outer bony plates. Turtle hips and

  shoulder bones lie more deeply inside the body, beneath the ribs—

  a startling arrangement because in humans and all other verte-

  brates the ribs lie beneath the shoulder (reach around and feel your

  own ribcage beneath the edge of your shoulder blade if you don't

  believe this statement). In order to get the ribs up and on top of

  the shoulder, the turtle embryo inside its egg must grow the ribs

  much more rapidly than usual, pushing the developing ribcage up

  and between the shoulder and hip, and attaching the rib edges to

  the underside of the shell bones. No other vertebrate—not even

  the tanklike nodosaurian dinosaurs—has ever evolved a mobile body

  armor so complete and effective as the turtles'.

  Turtle heads also command the respect of bioengineers. Tur-

  tle jaw and joints guide the chewing stroke into a long backward

  slide of the lower jaw against the upper. Toothless turtle beaks

  56 | THE CONQUERING COLD-BLOODS: A CONUNDRUM

  and palates are armed with horny cutting edges and multi-toothed

  shredding-crushing platforms. This basic masticatory apparatus is

  marvelously adaptable. Land tortoises shred tough grass. Giant sea

  turtles crush clams. Snapping turtles can slice up a dead trout or a

  drowned cow into chunks small enough to swallow. Right now, in

  the 1980s, my science is enjoying a turtle renaissance. Paleontol-

  ogists in Utah are investigating the muscular-electrical phenomena

  of turtle chewing by using sophisticated electromyographs, high-

  tech gadgets that chart each muscle's physiological activity. Field

  paleontologists at Berkeley are mapping the historical details of

  turtle evolution through Cretaceous and Paleocene strata. An em-

  inent New York anatomist is completely revising the turtle family

  tree. In scientific meetings all over the country the Turtle Renais-

  sance is shaking old-time zoology out of its complacency with the

  message: Turtles are complex, turtles are successful, turtles are

  worthy objects of research.

  The total turtle count—two hundred and thirty species—

  doesn't seem like an irresistible horde compared to the several

  thousand mammals in today's global ecosystem. However, turtles

  have scored quite an impressive ecological triumph in one very

  important role, that of freshwater predator-omnivore. Gavin Max-

  well's Ring of Bright Water is an absolutely charming otters' tale,

  the story of these sleek-furred aquatic mammals that frolic in the

  Scottish streams, catching salmon and crayfish and stirring up warm

  bemusement in human onlookers. All through the Temperate Zone,

  otters delight the naturalist and the lay public. But how many other

  freshwater, semi-aquatic mammal predators can you name? Mink,

  of course. Relatives of otters on one hand, land weasels on the

  other, mink do hunt in streams. How many others? If you caught

  the excellent BBC series "Life on Earth," you saw footage of the

  swimming shrew, the Desman of the Pyrenees, a molelike furball

  that dives for aquatic worms and other freshwater small fry. Our

  own New England star-nosed mole goes hunting in water, using

  its starburst-shaped snout tip to feel out wriggling prey. Andean

  streams flowing through Peru are host to the fish-spearing mouse,

  Ichthyomys, that impales prey on its projecting front teeth. But if

  we go to a tropical lake or sluggish river, is it full of otters, mink,

  and paddling shrews? No, it is full of turtles. The mass of tropical

  turtledom far exceeds the Mammalia in numbers of species in the

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  57

  aquatic-predator category. A few tropical otters do exist, and

  Uganda can boast of the giant otter shrew (a full two pounds in

  weight), but a single Congolese river system can display a dozen

  and a half specialized turtles, swimming after prey, eating fallen

  fruit and leaves, walking along the river bottom, scavenging pieces

  of hippo carcass.

  The entire subject of aquatic predation should embarrass the

  mammal chauvinist into silence. The lion may be king of the beasts

  on land, the top link in the terrestrial food chain. But in the Nile

  waters and in the great Rift Valley lakes of East Africa, the lion

  must fear for its crown. Here the king is the Nile crocodile. Con-

  trary to the popular view, crocodiles are neither sluggish, nor stu-

  pid, nor lacking in maternal affection. Crocodile mothers guard their

  nest with aggressive vigilance for the three-month incubation nec-

  essary for hatching. When the hatchlings chirp as they struggle to

  wrest free of the shell, the mother will gently help her newborn,

  lifting them in her jaws from nest to water's edge. For months a
fter

  hatching, the young crocodiles stay close to mother in the shal-

  lows, where she can drive away any potential threat. Field zoolo-

  gists in Georgia and Florida tell the same story of maternal care

  of our Mississippi alligator. (Alligators and crocodilians differ in

  shape only in minor features, the broader, flatter snout of the 'ga-

  tor being the most obvious; the term "crocodilian" encompasses

  all 'gators and crocodiles and their fish-eating kin, the frying-pan-

  headed gavial.)

  The Harvard professor's close call with the South Sea croco-

  dile is a warning that even the numero uno on nature's scale must

  be careful around crocodilians. Crocodiles are good hunters. An

  adult male will stick to one hunting territory for years, learning all

  the ins and outs of the watery passages among the reeds, gradually

  developing an ambush style calculated on the seasonal flux of fish,

  snails, turtles, and land mammals that come to the water's edge to

  drink. Adult crocodilians watch the shoreline, their heads sub-

  merged except for the bulging eyes and nostrils. If an antelope

  ventures close enough, the croc glides smoothly through the water,

  propelled by its deep, sculling tail. Five or six feet from the ante-

  lope may be close enough, then a quick lunge and the great rep-

  tilian jaws clamp shut on furry snout or leg. The thrashing victim

  is dragged under the water and stunned as the croc whirls around,

  58 | THE CONQUERING COLD-BLOODS: A CONUNDRUM

  rolling over and over. Sometimes a mammal victim escapes after

  one of its legs has been wrenched out of its socket. Lions, chee-

  tahs, and baby elephants have died this way. Not only Man but his

  domestic servants can be croc prey. A giant South Seas croc snagged

  a horse from an Australian farmyard and dragged it back to the

  billibog.

  Although such furry big game are key elements of many big-

  croc diets, most of the crocodilian clan subsist on less dramatic

  fare—fish of all kinds, aquatic turtles, swimming snakes, freshwa-

  ter mollusks. When just out of the egg, young 'gators and crocs

  hunt aquatic insects, frogs, and other humble game. Everywhere

  in tropical waterways the crocodilian ensemble—two dozen spe-

  cies—are by far the most important large semi-aquatic predators.

  All crocodilians are large by modern reptilian standards. None are

  as small as a Scottish otter, but adult size does vary from species

  to species. Giants among living species are the slender-snouted

  gavial of the Ganges and the estuarine crocodile of the Pacific

  shores. In both, a big male can exceed twenty feet in length and

  half a ton in weight. Tiniest are the heavily armored West African

  dwarf crocodiles and dwarf caimans of South America. In one dwarf

  species, females probably breed at the tender young length of two

  and a half feet. But these dwarfs make up for their size with ar-

  mor. All crocs have bony plates, sheathed in horn, embedded in

  the deep skin layer, and in dwarfs the plates make an especially

  tight-fitting mosaic, a flexible cuirass for chest and back. What's

  this protection for? Tigers and jaguars do pounce on careless little

  crocodilians caught basking on the shore, but the chief hunters of

  any given crocodilian species are other crocodilians.

  Ecological science, for reasons not clear to me, lacks the lyric

  eloquence of geology. Ecological terms rarely have the color or

  dynamism of such geologisms as "rift," "thrust fault," "mountain-

  building revolution," "hogback." Ecology tends rather toward the

  gray-flannel-suit metaphors of marketplace and commerce: "re-

  source partitioning," "energy budgets," and "investment." But

  modern ecological theory has given us one quite lovely term—the

  "guild." The clockmakers' guild in sixteenth-century Basle pro-

  tected the interests of all the makers of timepieces in that Swiss

  Protestant city. Guild councils enforced quality control and regu-

  lated the entry of new artisans into the urban market. An ecolog-

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  59

  ical guild is all the species that follow a particular way of making

  a living in local habitats. Hence the top-predator guild of the Ser-

  engeti is filled today by lion and leopard, cheetah and spotted hyena.

  Working the same landscape is the small-predator-scavenging guild,

  the golden jackal, black-backed jackal, Egyptian vulture, and grif-

  fon vulture. Reviewing our ecological census figures, we would be

  compelled to conclude that most tropical guilds are dominated by

  the "cold blooded" clans. In the small semi-aquatic guild of pred-

  ators, turtles are masters. The large-predator aquatic guild is firmly

  in the hands of a crocodilian cartel.

  I would hope that by now in our census through the verte-

  brate guilds the delusions of mammal superiority would be shaken.

  But we are not even half done. Remember, all the world's non-

  flying mammals add up to 3,000 species. There are now, by con-

  servative estimate, 3,000 lizard species and 2,700 of snakes.

  European culture and its American offspring are more igno-

  rant about lizards than about any other great divisions in the "cold-

  blooded" clans. Lizards don't abound in the cities of the Temper-

  ate Zone that served as cradles for Western science. Heidelberg,

  Paris, London, New Haven—all are great university towns, but all

  languish in a state of lizard impoverishment. Go to school in one

  of the Ivy League Colleges, take a field ecology course, and you

  will count yourself lucky to catch a glimpse of a little brown skink,

  speeding along a sunlit pathway. Turtles, frogs, salamanders, and

  snakes all outnumber lizard species in upper New York State or

  Massachusetts. Too bad, because the natural economy in the spe-

  cies-rich tropical world supports a dazzling lacertilian display.

  "Lacertilian," the standard label for all lizards, comes directly

  from the Latin lacerta, the Roman name for the common Mediter-

  ranean wall lizard, a hefty four-pounder that has hunted big in-

  sects around human habitation since the Parthenon was built, and

  before. (Spanish conquistadors called the broad-snouted crocodil-

  ian of the Mississippi el lacerto—a label that quickly degenerated

  into "alligator.") Travel south from the Mediterranean wall lizard

  country, past the sandy barrier of the Sahara, and you will reach a

  lacertilian evolutionary epicenter. Patrolling along the shorefront

  of the Nile are six-foot monitor lizards, long-tailed hunters that

  can swim, dig up croc nests with their strong foreclaws, and race

  off to escape predators by climbing a tree or descending a burrow.

  60 | THE CONQUERING COLD-BLOODS: A CONUNDRUM

  Locomotor triple threats, nearly all the dozens of monitor lizards

  can make quick progress in all modes, arboreal, terrestrial, and

  aquatic. Farther from water are snub-nosed savannah monitors, the

  lacertilian equivalent of badgers, truculent, stout-shouldered dig-

  gers that can exploit the buried resources of eggs, rodents, an
d

  fossorial reptiles.

  Whenever I see a stocky golden-skinned savannah monitor, I

  get a lump in my throat and misty eyes—memories of a wonderful

  sweet-tempered pet I had my second year as a graduate student.

  Part of the task for my thesis was to measure metabolism during

  walking in lizards, so we could calculate an ecological energy bud-

  get for dinosaurs. After three frustrating months of failed experi-

  ments with skinks, race runners, and desert iguanas, I reluctantly

  concluded that even though it was small-brained, the average liz-

  ard was smart enough and mean enough not to consent to walking

  on a treadmill for an hour while wearing a lizard-size gas mask with

  two hoses attached to a great big Beckman oxygen analyzer with

  a battery of blinking lights emitting clicking instrument noises. But

  then I acquired G. Hawn, the gold-colored monitor. She ran

  beautifully, and we got excellent data. And she was a quick learner.

  We had to run the lizards when their stomachs were empty, be-

  cause digestive metabolism complicates the measurements of ex-

  ercise. G. Hawn learned that she would be fed two plump white

  mice, alive and fresh, and a raw egg at the end of a successful run.

  She soon was giving us two good long runs each week. Alas, she

  succumbed suddenly to a respiratory infection, untreatable be-

  cause lacertilian veterinary medicine is still very crude. No mam-

  mal chauvinist can tell me that lizards can't be clever. I can't claim

  that my monitor responded to me with affection, but her viva-

  cious character certainly elicited that response from her owner.

  Both Nile monitor and savannah monitor are snail-boppers, a

  prey especially attractive to lizards. Adult lizards from the two

  species go about with swollen acorn-shaped teeth, pestles that can

  crack even the most resistant-shelled mollusks. Such evolutionary

  enthusiasm for shellfish might seem surprising, but in fact tropical

  habitats of all climates offer a tempting menu of multi-species es-

  cargot, because snails are among the most diverse of the land and

  aquatic animals. Although not many lacertilians are specialized

  swimmers—unlike their distant scaly relatives, the turtles and croc-

  MESOZOIC CLASS WARFARE: COLD-BLOODS VERSUS THE FABULOUS FURBALLS I 61

  Dragon lizards, past and present. Today Komodo Dragons reach nine feet