Tyrannosaurs: It’s Not Just About Rex
Posted by Richard Conniff on July 16, 2016
by Richard Conniff/Wall Street Journal
Given that tyrannosaurs are the most studied of all dinosaurs, and familiar to almost everyone above the age of 5 (or maybe make that 3), it’s extraordinary how little we really know about them: huge bodies, big spiky teeth, tiny arms, scary as hell. That’s about it for most of us.
Go a little deeper and we mostly go wrong, according to David Hone, a paleontologist at the University of London. “Tyrannosaurs,” he writes, in “The Tyrannosaur Chronicles,” “were not pure scavengers; they didn’t spend their lives battling adult Triceratops, they did not have poor eyesight, they could not run at 50 km/h, females were not bigger than males,” and they weren’t all Tyrannosaurus rex, that flesh-rending, scenery-chomping, lunkheaded box-office giant of our nightmares.
Mr. Hone’s unsensational and resolutely middle-of-the-road account lists 29 tyrannosaur species. He adds that
he had to change that number three times while working on the book, because scientists have been discovering about one new tyrannosaur species a year for the past decade. Our obsession with giants like “Sue,” the celebrated Tyrannosaurus rex specimen at Chicago’s Field Museum, which measured more than 42 feet in length and weighed more than 15,000 pounds when alive, may be misplaced. Most tyrannosaurs were comparatively small—as little as 2 feet in length, with the tail accounting for half of that.
The tyrannosaurs, Mr. Hone explains, lived and evolved over a period of some 100 million years—from 167 million years ago to the dinosaur apocalypse 66 million years ago—and they roamed Asia, North America and Europe, and possibly beyond. They stayed small to midsize until the multi-ton giants came along in the final 15 million or 20 million years of tyrannosaur evolution. But it’s safe to say that all of them would have made for unpleasant company. That diorama at the Creation Museum depicting smiling children playing in a lush garden beside two tyrannosaurs? It’s wrong in so many ways, but mostly because the smile would have been on the tyrannosaurs.
Mr. Hone begins his book with a primer on basic anatomy, including helpful illustrations to take readers from premaxilla bones (just below the nostrils, or nares) to caudal vertebrae, and to sort out ilium from ischium. He goes on to explain that a primordial mutation gave some ancestral carnivore somewhere in Asia “more robust premaxillary teeth.” And thus the kings, or more properly tyrants, of the dinosaur world began their reign of terror.
Those spiky teeth, D-shaped in cross-section and serrated on the inner edge, together with fused nasal bones to make the skull strong enough for its massive bite, became the defining tyrannosaur features. Though museum specimens and illustrations tend to depict neat rows of teeth that would make a tyrannosaur orthodontist proud, the reality would have been spottier: Tyrannosaurs routinely shed and replaced teeth in the course of their flesh-rending and bone-crushing. “A single tyrannosaur that lived for a decade or more might thus go
through hundreds, or even a thousand or so, teeth in a lifetime,” Mr. Hone writes. In any case, paleontologists increasingly suspect that the whole nasty array may have been hidden behind lips. (The better to smile with, my dear?)
Mr. Hone does a good job of explaining the long odds against a carcass becoming fossilized in the first place and the astronomical odds against the skin and other soft tissues being preserved. For paleontologists to rediscover and make sense of an entire superfamily of extinct species across tens of millions of years seems nearly miraculous. Though their nicknames (“Sue,” “Bucky,” “Stan,” “Scotty”) make them sound as familiar as grade-school classmates, “we have at best perhaps 30 or so decent specimens of the largest tyrannosaurines,” Mr. Hone writes.
There are as a result more questions and theories about them than answers: Were tyrannosaurs sit-and-wait predators, like cheetahs? Or was their gait—head low, tail up—efficient enough, even if not particularly quick, to engage in extended pursuit of prey, or even some form of group hunting, like wolves? Why did the arms become smaller over the course of evolution? (Mr. Hone suggests that big, powerful arms would have been deadweight as the powerful head and teeth took over all the bloody work of killing.) Were they social creatures? Did they provide parental care and bring food to their young? If they spent much of their lives sleeping, like modern predators, how did they get back on their feet again?
And, speaking of awkward, how do 15,000-pound serial killers have sex? Mr. Hone notes that birds, now recognized as the only dinosaurs to have survived the great extinction 66 million years ago, commonly mate “with little more action” than pushing their cloacas—the combined excretory-genital openings—together in what’s known elsewhere as a “cloacal kiss.” But given that tyrannosaurs had a huge, heavily muscled tail in the way, this might well have been an air kiss. Mr. Hone’s proposal is that we seek hints in the strange sex lives of ducks: “An explosively inflating organ that is both longer than the animal that bears it and helical in shape is really only the start.” And you thought tyrannosaurs couldn’t get any scarier.
It also suggests just how dramatically our theories about them can change with the discovery of new evidence. For instance, unearthing Yutyrannus, the “feathered giant” found in northeastern China in 2012, has left many paleontologists thinking that even Tyrannosaurus rex may well have been feathered and brightly colored.
At times, Mr. Hone becomes too focused on the details and neglects to bring aspects of the story to life. It’s intriguing to know that tyrannosaurs had hollow, pneumatic bones. But his explanation of how the hollow spaces in the bones functioned as part of the respiratory tract left me baffled, and he offers no hint of how they might have affected tyrannosaur locomotion.
He also misses a major opportunity for engaging readers by almost completely omitting the colorful stories of the characters who have made the discoveries, developed the theories and then fought about them. The few times he does mention them, it’s not in a way that encourages confidence. It’s odd to describe Henry Fairfield Osborn as “a great American paleontologist of the 1800s,” because the modern consensus is that his science wasn’t so great. Not to mention that he described and named Tyrannosaurus rex in 1905 and continued to work almost until his death in 1935.
But these are quibbles. For readers who got hooked on tyrannosaurs as 5-year-olds, and want to know more at 15 or 50, this book is a useful introduction to some of the most wonderfully terrifying animals ever to walk the Earth.
If you’d enjoy some of those stories of discovery, check out my new book House of Lost Worlds: Dinosaurs, Dynasties, and the Story of Life on Earth (Yale, 2016).