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Extreme Makeover
We bring T. rex and kin into the 21st century.
May/June 2008
by Bruce Fellman

Bruce Fellman is the managing editor of the Yale Alumni Magazine.

Illustrations ©Alan Male & Rudolph Zallinger '42BFA, '71MFA

When the current headquarters of the Peabody Museum of Natural History opened in 1925, its hangar-sized Great Hall, then as now, was the centerpiece of its exhibits—filled with the likes of Stegosaurus, Triceratops, and other massive fossils unearthed by Othniel Charles Marsh, Yale’s first paleontology professor and a celebrated nineteenth-century bone hunter. Nevertheless, in the early 1940s, Peabody director Albert Parr found the room wanting. Its walls were too gray and drab. Perhaps, he said, they could be “spruced up.”

Parr had already hired a Yale School of Fine Arts student, Rudolph Zallinger '42BFA, '71MFA, to produce some illustrations of seaweed. Might Zallinger be interested in a slightly larger challenge? Parr’s idea was to bring the fossils to life with a series of dinosaur paintings on panels on the east wall. But Zallinger was more ambitious. He proposed a “panorama of time”: a mural 110 feet long and 16 feet tall, telling the complete story of dinosaur evolution, from the emergence of the dinosaurs' ancestors in Devonian swamps 362 million years ago to the demise of the “ruling reptiles,” 65 million years ago at the end of the Cretaceous Period.

Zallinger started the project in 1942 and completed it on June 6, 1947. As spruce-ups go, The Age of Reptiles was a colossal success. It was featured on the cover of Life magazine in 1953, as well as on a U.S. postage stamp in 1970. For young scientists of the time, it was inspiring, says Yale paleobotanist Leo Hickey: “This room has been called the Sistine Chapel of evolution.”

Scientifically, says Yale paleontologist and geology professor Jacques Gauthier, “the Zallinger mural was the leading-edge production of its time." Zallinger had gotten a crash course in dinosaur science from some of the best researchers at Yale and Harvard, and his mentors constantly checked in to make sure his representation was as accurate as possible.

But current science has turned The Age of Reptiles into its own kind of dinosaur. In the 1940s, the prevailing view of dinosaurs “was that they were a bunch of big, slow-moving, stupid, cold-blooded clunkers,” says Gauthier. And no one subscribes to that notion anymore, says Jack Horner, Regents Professor of Paleontology at Montana State University-Bozeman (and the inspiration for Alan Grant, the lead character in Jurassic Park). There’s been a revolution in our way of thinking about dinosaurs, and much of it, according to Horner, can be traced back to one man—John Ostrom, who joined the Yale faculty in 1961. “John rebuilt our image of dinosaurs,” Horner says.

In 1964, on the last day of a prospecting trip in the Montana badlands, Ostrom and his field assistant, Grant Meyer, found one of the most important fossils in the history of paleontology. They noticed some large, sharp claws protruding from a hillside, and they “both nearly rolled down the slope in our rush to the spot,” Ostrom later recalled. “It was evident … that we had stumbled across something very unusual and quite unlike any previously reported dinosaur.”

Ostrom named the find Deinonychus antirrhopus—“counterbalancing terrible claw”—after the lethal, sickle-shaped claw on each of the animal’s feet, clearly used to slash or stab prey. This ten-foot-long predator, he proposed, was no slow-moving clunker but a lithe, athletic, intelligent hunter. Thus began the revolution.

Ostrom even suggested that Deinonychus was warm-blooded. It was a heretical concept that had been out of favor for a century. “John’s speculations were greeted with shrieks of horror by the traditionalists,” says Robert Bakker '67, who worked with Ostrom as a field assistant and would later champion the idea of warm-bloodedness. (Bakker traces his interest in paleontology to Zallinger's mural.)

The discovery of Deinonychus helped set off a flurry of new work on dinosaurs. Today the jury is still out on the question of their metabolism, but another of Ostrom’s heresies has become gospel. (Ostrom died in 2005.) In the early 1970s, he analyzed the skeleton of Archaeopteryx, the first bird, and found so many similarities between it and Deinonychus that in 1973 he suggested they were close relatives.

He went further (and resurrected another long-derided theory) by concluding that Deinonychus and many of its cousins, including Tyrannosaurus rex, had had feathers. His deduction was verified in the 1990s when researchers digging in northeastern China discovered a trove of exquisitely preserved, 120-million-year-old feathered dinosaurs. For most paleontologists, the Liaoning fossils clinched the argument that today’s birds are descended from dinosaurs.

Ostrom’s discoveries and insights, says Jacques Gauthier, “started a genuine dinosaur renaissance.” Today, dinosaur researchers have found evidence for a plethora of behaviors and abilities that were once thought to be exclusively the province of birds and mammals.

Many dinosaurs, Deinonychus included, laid eggs and brooded them in nests. Some dinosaurs protected their young; many species traveled, no doubt for safety and mutual interest, in herds made up of individuals of all sizes and ages. Hadrosaurs (or duck-billed dinosaurs), such as Parasaurolophus walkeri, may have communicated with their herds by forcing air through the hollow pipelike structures on their heads. Males of some species, like Pachycephalosaurus, probably fought each other for access to females.

Below, Yale paleontologists Leo Hickey, Jacques Gauthier, and Daniel Brinkman provide a guided tour of The Age of Reptiles, showing where the prevailing wisdom of the day sent the painter down the wrong path. The Yale Alumni Magazine commissioned dinosaur artist Alan Male to update a section of the mural—from about the time depicted in Jurassic Park to that split second, 65 million years ago, just before a huge meteor slammed into the Earth and helped send T. rex and its Cretaceous relatives into extinction.

The Peabody intends to update The Age of Reptiles—but only virtually—as part of a twenty-first-century sprucing up. The mural will not be painted over; instead, the museum will install interactive touchscreens and multimedia displays in the Great Hall, where visitors will be able to study up-to-date illustrations and read about current dinosaur science. It’s a certainty that new research will necessitate frequent revisions. 

The Age of Reptiles mural in the Peabody Museum spans 110 feet and nearly 300 million years. We asked an artist to show what a version of the leftmost sections—the Jurassic and Cretaceous periods—might look like if painted with today’s knowledge of dinosaurs.

(1) Volcanoes, plus a meteor

(2) Lord of the jungle

In both the Peabody’s 1947 mural and Alan Male’s update for the Yale Alumni Magazine, a fearsome Tyrannosaurus rex lords it over the landscape. But paleontologists now believe the uber-predator was trim and colorful. Alan Male’s is most likely a teenager. “Young tyrannosaurs definitely had feathers,” says Gauthier, “and these, or some kind of down, lasted at least until adolescence. You see this pattern in elephants—the juveniles are hairier than the adults. Perhaps it was also true in T. rex. ”

(3) Triceratops

The three horns of Triceratops and the frill behind the animal’s head were probably used for defense and helped members of the species to recognize each other. Experts are divided over how quickly Triceratops could move, but they agree that its legs were not splayed to the side, lizard-fashion, as they appear in the Peabody mural. The new posture suggests a less lumbering, more alert beast—no easy prey for T. rex, notes Gauthier. “Triceratops was a very dynamic animal.”

(4) Herd behavior

Hadrosaurs (or duck-billed dinosaurs) such as Edmontosaurus often traveled in herds made up of animals of different ages and sizes—think North American buffalo or African wildebeest. These vegetarian dinosaurs had scales rather than feathers. Many had large noses, and some had hollow crests, both of which were probably used to make hooting sounds to call potential mates or alert the herd to danger. “Duckbills may have undergone regular, long-distance migrations to lay their eggs or move in search of food,” adds Gauthier. “An Edmontosaurus herd would have had quite an environmental impact.”

(5) Floral display

“T. rex wouldn’t have stopped to smell the magnolias,” says paleobotanist Leo Hickey. “Springtime in the Cretaceous was not showy.” Flowering plants had evolved by then, but many of the flowers of that era were small and inconspicuous, the blossoms typically opening one at a time rather than en masse. Beetles did most of the pollinating.

(6) Tanks

The ankylosaurs (or tank dinosaurs) were short, stocky, and armor-plated, often in the extreme. To refine the painting’s flow of geologic time, paleontologist Daniel Brinkman suggested replacing its Ankylosaurus—a contemporary of T. rex at the end of the Cretaceous, 65 million years ago—with Sauropelta, a relative that lived about 110 million years ago.

(7) Palms vs. cycads

The Peabody mural features a lush swamp as the landscape of the early Cretaceous and late Jurassic, 110 to 150 million years ago. But much of the flora, says paleobotanist Leo Hickey, was “totally wrong.” He finds the wide-leaved vegetation along the edges of the stream baffling: “I don’t know what these plants are—there’s no fossil evidence for them.” Nor did large palms exist yet. “Rudy [Zallinger, the painter] didn’t really have a good feeling for trees,” says Hickey. The dominant plants were actually palmetto-like species, smaller than palms; cycads; and lots of horsetails.

(8) Water lover?

In the 1940s, Brontosaurus was thought to be so massive and slow that it spent most of its time in the water—both to support its weight and to deter predators. But that’s “an urban legend,” says paleontologist Gauthier. “An animal that big, which had a big whip attached to its tail, was not at all defenseless.”

(9) …or impostor?

In fact, there never really was a Brontosaurus. The fossil that O. C. Marsh named Brontosaurus was actually the same as a kind of dinosaur he had discovered earlier—the Apatosaurus. Marsh also got the head wrong on “Brontosaurus. “ His specimen lacked a skull, so he made an educated, but ultimately inaccurate, guess; the animal had a slimmer, more elongated head. And finally, “we now know that the tail posture is wrong” in the Peabody mural, says Gauthier. Scientists have found that sauropods, the group of massive, plant-eating dinosaurs to which Apatosaurus belonged, probably walked with tails extended straight behind. Indeed, the tail in the Peabody’s original “Brontosaurus” display had to be broken for it to drape along the ground.

(10) Revolutionary

Deinonychus was unknown when Zallinger painted the Peabody’s mural. The discovery of this lithe, fast (and perhaps even warm-blooded) predator in 1964 by Yale’s John Ostrom launched the current revolution in our understanding of dinosaurs. The feathers in Alan Male’s painting are a conjecture—feathers are rarely fossilized, and none have been found on Deinonychus fossils—but a very likely one, as Deinonychus’s closest relatives had them.

Ostrom suggested that Deinonychus hunted in cooperative packs, like wolf packs, because the animals have been found fossilized in groups and the footprints of many individuals have been found in trackways. But Peabody paleontologist Brinkman thinks Deinonychus was more likely “a solitary hunter in the manner of the Komodo dragon. One lucky predator kills as an individual, and then others in the area smell something and come running. This loose aggregation lasts until the food’s gone; it’s not a permanent pack.”

(11) Plant defenses

“Think of Apatosaurus, “ says Hickey, “as a weedwhacker”—that is, a high-volume plant-eater that primarily consumed brush and ground cover. But it could also reach higher leaves and branches by balancing on its hind legs and tail, tripod-style. Hickey says the shape of Araucaria evergreens, with their needles concentrated  high off the ground, may have evolved in response to Apatosaurus and other sauropods.

(12) Buff

Stegosaurus, another dinosaur named by Yale’s O. C. Marsh, was an enigma: what was the purpose of those large plates on its back? Marsh suggested that they covered the animal as a kind of armor, but later fossil discoveries revealed that the plates stood upright. More recent theories hold that the plate and spike patterns in stegosaurs were unique to each species—so they were useful for defense, but were just as important as a colorful means of attracting the opposite sex. And Stegosaurus is no longer thought of as a lumbering, slow-moving beast but as mobile and formidable.  

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