Dr. Robert Bakker Answers Your Questions

Dr. Robert Bakker Answers Your Questions 47

Posted by samzenpus on Monday March 11, 2013 @11:33AM from the listen-up dept.

A while ago you had the chance to ask paleontologist Dr. Robert Bakker a wide variety of questions. Instead of answering them individually, Dr. Bob decided to write a lengthy piece that covers most of your inquiries, and includes personal stories and some of his philosophy. The first part is a narrative about his childhood conversion to fossil studies and how his paleo-CSI approach developed. We'll post the second half, covering his training in the history of theology and how it intersects with his science, tomorrow.

A digital scan of a shot I took of Rudy Zallinger’s oil sketch for the 1948 “The Age of Reptiles.” Part of the grand “Life Magazine” issue of 1953.

Reading Lincoln Barnett, Staff Writer, Life Magazine, 1955.

I never got to meet Lincoln Barnett and thank him for getting me into paleontology. It’s my greatest regret..

.....it’s still a vivid memory : me in the sun room of my granddad’s house, opening the Life Magazine of Sept. 7, 1953. The issue had been lying on the table for 18 months but I hadn’t noticed it before. Jurassic behemoths on the cover, pull-out murals inside portraying hundreds of prehistoric wonders. But it wasn’t the simple parade of monsters that hooked me. It was the grand saga of life and evolution, and how dinosaurs fit in the flow of Deep Time. It was the grandest tale I had read.

At the time I was a fourth-grade military-history buff, a ten-year-old expert in the history of naval architecture. I scratch-built models of Athenian triremes for Salamis, Venetian galleasses for Lepanto, and the high-sided cruiser Olympia for Dewey’s 1898 victory at Manila Bay. I lectured friends on why the HMS Invincible was perfect to win the Battle of the Falklands and yet was destined to lose catastrophically at Jutland. But the Life Magazine revealed a history far more complicated and far more fascinating. Mr. Barnett wrote of powerful machines built of muscles, bone and ligaments, equipped with the terrible weaponry of teeth and claws. These living machines were designed for fighting and feeding and reproducing.....and conquering the ecosystem. And for evolving.

The year 1953 was before the Double Helix was decoded and before the acceptance of plate tectonics by the English-Speaking world (South African geologists had seen the evidence and believed). Still, Barnett and the artists at Life put their fossils in context of Darwinian process -- how chromosomes segregated and mutated, providing the raw material for natural selection. To explain speciation they enlisted the most hauntingly beautiful of all vertebrates, the Birds of Paradise in Papua. No one, not even a ten-year old military geek, could ignore those birds and the story of how mountain gorges had separated populations and created new species. Then another painting demonstrated how habitat differences -- the color of the ground -- drove adaptive divergence in ground-running lizards.

So, from one single magazine article, I came to understand allopatric speciation and adaptive divergence. Not bad.......

Barnett’s introductory passages set me up to appreciate Deep Time. One-celled critters rowing themselves through primordial seas with their banks of cilia were first, followed by the explosion of trilobites and the earliest known fish-oids, petrified in the Burgess Shale. Then I met the lobe-finned fish and the ur-amphibians, Ichthyostegas, bravely propelling their squatty-bodies on stubby but efficient limbs.

I remember staring at the brace of Permian fin-backs, Dimetrodon the hunter and Edaphosaurus the vegan. They were the very first large land critters who could play the roles of Top Predator and Top Herbivore. The Early Triassic ushered in the mammal-like reptile, Cynognathus, glowering like a junk-yard dog crossed with a Gila Monster. He seemed to be thinking deep thoughts about his place in nature. Dinosaurs? Yes, I got to them with the Late Triassic Plateosaurus. And then there were sumptuous double-page spreads of the Late Jurassic and Late Cretaceous. The final spreads portrayed the opening of the Cenozoic and the explosion of furry and hairy clans that evolved to fill the voids left by dino-extinction.

Life and Barnett didn’t rush me. They put the famous dinos in their proper place in the entire billion-year saga. Now, in 2013, I get irritated at some kids’ books: they jump right into the Jurassic monsters without taking enough time to set the stage properly with the Paleozoic. And that kind of book usually short-changes the Age of Mammals as well.

In the evening after pouring over the Life magazine, I announced to my startled parents that “...I’m gonna grow up to be a paleontologist....and study the fossil story.” Mom smiled and replied “That’s nice dear....it’s a stage...you’ll outgrow it.” She still says that.

The next weekend, off to the Ridgewood New Jersey Public Library I went. There were a dozen fossil-books, most illustrated in glorious black and white. I sensed that evolutionary history was one, fabulous transitive game.

Thanks to naval history, I already understood transitive games. Our first U.S. dreadnought, the 1909 Michigan, could beat our last pre-dreadnought the 1906 Vermont, but, in turn could be beaten by the second wave of dreadnoughts like the 1913 Nevada. And the Nevada wouldn’t last long in a duel with our last dreadnought, the 1943 New Jersey. Each new ship design was more progressive, better armed, better armored, better able to absorb punishment. In the history of life, the waves of Top Predators and Top Herbivores seemed to obey simple transitive rules too: each new clan was a improvement in brains and hearts, lungs and limbs. The earliest Top Predators and Herbivores, Dimetrodon and Edaphosaurus, were built by Natural Selection to a lowly design, like a lizard’s. These fin-backs were replaced by Cynognathus and its kin because the cynognaths carried more progressive anatomical weapons. In dinosaur history, the Triassic Plateosaurus, an ur-veggie-saur, gave way to more sophisticated design, the Jurassic Brontosaurus. In the Age of Mammals, the same rules operated. Early big mammals, both carnivores and herbivores, were small-brained and clumsy. They were replaced by big-brained, swift-running horses and wolves and saber-toothed cats.

But I detected a monstrous glitch in the Transitive Rules. Cynognathus was, according all the sources at my fourth-grade disposal, almost a mammal. Therefore, it must have been equipped with almost-hot-blooded brains, hearts and lungs. So it must have been designed to beat any regular cold-blooded reptile. Here’s the problem. Cynognathus and company were replaced by......the early dinosaurs. And dinos were regular reptiles, cold-blooded, stupid and slow. Oh....and bad parents. So said all the books in the library in the 1950’s. That didn’t make transitive sense........dinos beating cynognaths was like a battle line of pre-dreadnoughts whipping the four New Jerseys.

Scan of a photo of my childhood copy of the Zallinger mural, reproduced in the Golden Book of Prehistoric Animals.

American Museum 1955 -- Ned Colbert’s Dinosaur Halls.

A few months after my fateful meeting with Mr. Lincoln Barnett, I went on a school field trip to the great fossil-halls at Central Park West and 79th Street, the American Museum of Natural History. The exhibits had just been renovated by Curator Ned Colbert. Colbert’s hall design put fish and fin-backs, dinos and saber-tooths, in ecological contexts. His displays were festooned with art -- paintings, drawings, sculpture. In the 1980’s Colbert’s halls were criticized for not being cladistic enough (not concentrating on family trees); such griping is churlish. His displays achieved a vivacity has never been surpassed and rarely equaled.

The Early Permian exhibits had real bone skeletons for all the key guilds: Top Predator, Dimetrodon, Top Herbivore, Edaphosaurus, Gator-style aquatic predator, the amphibian Eryops. The Late Jurassic dino-island was arranged as a living prehistoric zoo. Animals who were buried together were mounted together. Stegosaurs and diminutive camptosaurs were mounted as if eyeing the raptor-like Ornitholestes. The Jurassic tableau was arranged exactly as in the painting in Life!

The single most astonishing display in Colbert’s hall, and the one that inspires my own field work to this present day, was the allosaur-brontosaur kill scene. A marvelous adult allosaur skeleton was mounted in a crouch, as if had paused in its feeding upon the rump of an enormous brontosaur. The museum label said: “....tooth marks on the brontosaur bones match the dentition of the Allosaurus.” That spare sentence was galvanic. The painting of the Jurassic predator and its prey was not mere speculation. It was not a flight of paleontologic fancy. It was dinosaur CSI, Jurassic Crime Scene Investigation (that phrase had not yet been made famous by tv). A little reading in the museum library confirmed the conclusion. The allosaur skeleton and chewed brontosaur had been dug from the very same thin layer of dark mudstone, only a few miles apart, at Como Bluff, Wyoming. Quite possibly, predator and prey had coexisted, had even sniffed each other. Certainly the population of allosaurs and the population of brontosaurs had interacted over hundreds of generations. And so...it was quite reasonable to suppose that an allosaur very like the one mounted in the museum had, indeed, gnashed its fangs on that bronto-hindquarters.

The marvelous Jurassic crime scene -- the New York allosaur feeds on a brontosaur. From the 1917 guidebook by W. D. Matthew.

Later, as a college undergrad, I met the painter of the Life mural, Rudy Zallinger, who explained that his Jurassic scene was indeed inspired by those very New York specimens. The allosaur/brontosaur dyad had been celebrated in the earliest version of the hall, back in 1907, by the first famous dino-artist, the magisterial Charles R. Knight. Rudy wove together all the fossils and the previous artistic visions, Coal Age to Ice Age, and had won a Pulitzer Prize in 1949. Rudy was a peach, and I did have opportunities to thank him profusely for getting me into science.

The New York predator/prey scene worked on my mind. Fossils did record actual living creatures performing their ecological chores, contributing to Darwinian progress.

Fossil CSI and My Favorite Dino -- Ceratosaurus nasicornus, Terror of the Lungfish.

Ceratosaurus is and has been my favorite dino since 1958. This is a minority taste. I’ve met only one dino-digger who rated it #1 in desirability -- the late, great James Madsen, who worked the Cleveland Lloyd Quarry in the Late Jurassic of Utah. I first met Ceratosaurus in a drawing in the “The Fossil Book”, by Fenton and Fenton, a marvelous volume that is still the best introduction to all fossils, from foraminifera to mammoths. The sharp-edged, ovate horn on the ceratosaur nose was intriguing, as was the low, slinky body, far less stiff than that of contemporaneous allosaurs. Life Magazine had no ceratosaurs, nor did the New York museum. I had to wait until my first trip to the Smithsonian to greet the type skeleton, half enclosed in a sandstone slab, like a Jurassic version of Michelangelo’s bound slave. The teeth were terrific -- twice as large for the skull size than those in an allosaur’s mouth. And far sharper as well. Torso was lower, slinkier than an allosaur’s, and the tail was very much more sinuous.

What did ceratosaurs eat? What habitat did they chose? Where did they fit in the waves of Darwinian progress? More broadly I asked myself “how can we reconstruct the activity of extinct predators throughout the different habitats of the Jurassic?” As a college senior, the first grant proposal I wrote was to the National Geographic Society to pursue this inquiry. I went on to spend two decades trailing ceratosaurs, taking the CSI hint from the New York museum. We searched for what we called “Jurassic Ballistics.” It goes like this: nearly all dinos, and crocs and lizards (but not us mammals), grow new teeth from birth to death. Each tooth-socket works like a gun with a magazine that never runs out of “bullets” = tooth crowns. As each new crown grows up through the socket, the old crown is forced out. The old root gets dissolved by body chemistry, just as the cartridge case is ejected from a gun when the bullet is fired. We say the crown is “fired” from the socket “barrel”. Those “fired” tooth crowns, in theory, can tell us who was feeding where. We searched assiduously for “dental bullets” all over Wyoming’s Late Jurassic outcrops. We found that allosaur bullets were concentrated within masses of herbivore carcasses. Tiny hatchling allosaur crowns were mingled with crowns from full grown adults - proof that young and old fed at the same spot at the same time. Were young and adults part of the same family? Circumstantial evidence pointed this way.

The allosaur tooth guns -- each socket grows a never-ending sequence of crowns.

Shed crowns from baby allosaurs who were no bigger than a house cat were excavated next to huge prey carcasses, up to forty thousand pounds in body weight. We found no tiny prey of a size suitable for the young allosaurs to have hunted by themselves. Individual prey bones had tooth marks left by baby allosaurs and adults, and often the baby marks and adult marks crossed. Yes -- the crime scene ballistics did point to simultaneous feeding by baby and adults on large prey acquired by adults.

Later digs in the Late Cretaceous provided ballistic evidence that tyrannosaur species fed in families too. The Black Hills Institute excavated a fine adult Triceratops who had tooth-marked bones (specimen now on display at The Childrens Museum of Indianapolis, a superb institution). All around the T’tops were some forty shed teeth, juvenile and adult, from the small tyrannosaurid Nanotyrannus. Clearly young and full-grown predators had fed together.

(Some colleagues have accused Nano’s of being juvenile T. rexes; new finds debunk the idea. The “Dueling Dinosaurs of Montana” discovery includes a full grown Nano that demonstrates the key differences: Adult Nano’s have heads and bodies only half the size of a full-grown T. rex but the Nano arms and fingers are twice as massive and carry claws that dwarf those of a rex. At all growth stages, Nano teeth are far sharper than rex chompers.)

Back to the hunt for Ceratosaurus habitats. Wherever allosaur shed teeth were abundant, ceratosaur bullets were extraordinarily rare. The first ten years we found only one shed fang next to a carcass from a camarasaur (thin-necked cousin of the brontosaurs).

At last, in 1990, we rumbled into one unusual habitat: wide Late Jurassic lake beds. Here dinosaur prey were scarce. Most bones came from crocodiles and giant lungfish up to 1,000 pounds in body weight. Some of the lungfish skull bones had deep gashes inflicted by predator fangs, and all the lungfish remains were surrounded by dozens of huge dinosaur bullets left by some giant fish-eater.

The Ballistic evidence spoke: most of the shed crowns came from none other than Ceratosaurus. At last I had a picture of adaptive divergence among Jurassic Top Predators. The slinky, sinuous body and tail of ceratosaurs would have been an advantage in swimming, a better hydrodynamic design than that of the allosaurs. On the other hand, allosaurs had longer legs and more compact torsos, design features permitting faster runs on drier, more open habitats.

My favorite dino --- Ceratosaurus, whose teeth were twice the size of an allosaur’s of the same head size.

The long-term pattern of evolution among Jurassic Top Predators was fascinating. Early in the Jurassic, long, slinky bodies were the equipment carried by the dominant Top Predators in wet AND dry habitats. But in the later Jurassic, longer-limbed, faster allosaur-style predators had displaced the more primitive, more sinuous carnivores from most habitats -- except those near large bodies of water. It was reminiscent of what would happen much later, in big-cat evolution. Leopards retained the primitive, slinky, low-slung design of the oldest big felids. The design is still ideal for hunting from ambush in dense bush or broken terrain. Or swimming across rain forest rivers. But cheetahs diverged from the ur-cat shape and evolved long legs and taller posture, for long-distance chases over open savannah.

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