Paleontologist Stephen Brusatte has helped identify new relatives of T. Rex.
By Brooke E. O’Neill, AM’04
Photography by Mick Ellison
“Brachiopods just don’t do it for me,” says Brusatte, so he started working with dinosaurs.
As a high schooler in central Illinois, Stephen Brusatte, SB’06, spent many summer afternoons exploring sites such as LaSalle Limestone, a cement-mining area known for its prehistoric remnants. With a teacher and on his own, Brusatte scoured local quarries, uncovering 280-million-year-old shark teeth, corals, and shells of marine invertebrates called brachiopods. The process not only taught him how to decipher geologic maps and collect specimens, but it also sparked the realization that “brachiopods just don’t do it for me.”
So he moved on to bigger bones. Today his fossil subjects include Tyrannosaurus rex and its cousins; his dig sites the American West, Lithuania, and Tibet; and his collaborators U of C paleontologist Paul Sereno. A doctoral student at Columbia University and the American Museum of Natural History, in October he was the lead author on a paper describing the T. rex family’s most recently discovered and most unusual members, the Alioramus altai. Unearthed in Mongolia’s Gobi Desert during a 2001 expedition—Brusatte, in high school at the time, was not on the dig—the long-snouted carnivore bears eight facial horns and a delicate skeleton made more for speed than strength. The discovery has forced researchers to redefine what it means to be a tyrannosaur. Unlike the bulky T. rex “super predators” that dominated the final part of the Late Cretaceous period (84–65 million years ago), their contemporary relative Alioramus relied on quickness and stealth to hunt smaller prey. Compared to T. rex, Brusatte says, “this new animal is like a ballerina.”
To trace the family connection, he compared the fossil’s anatomy to that of other carnivorous dinosaurs. Relying on computer analysis and a dataset of more than 300 skeletal features, he discovered that Alioramus and T. rex share skull, limb, and vertebrae traits.
The findings, published in the October 5 Proceedings of the National Academy of Sciences, came on the heels of another unexpected find: the small Raptorex kriegsteini. With its strong jaws, massive head, and undersized forelimbs, it shares the characteristic T. rex body structure, yet, at ten feet long, it’s only about a 100th of the larger creature’s body mass. “That’s a totally bizarre animal,” says Brusatte, who worked with Sereno, his longtime mentor, to identify the 125-million-year-old cousin.
Surprises like Alioramus and Raptorex help Brusatte and his colleagues fill gaps in prehistoric genealogies. “The ultimate goal,” he says, “is to say something concrete about the evolution of these animals over a long time scale.” As a 2006 Marshall scholar at the University of Bristol, for example, he analyzed family trees to show that crocodile relatives during the Late Triassic period (230–200 million years ago) were “really outdoing” early dinosaurs. “You look at crocs now, and they all kind of look the same,” says Brusatte, “but back then there was this great diversity” of facial and body structure, of diet, of lifestyle. That research, published in Science in 2008, countered longstanding claims that dinosaurs outcompeted other Triassic reptiles. In reality, says Brusatte, dinosaurs were a minor group, the “beneficiaries of a mass extinction event that changed the rules of the game” by killing off most of the crocodile relatives.
A frequent elementary-school speaker and the author of three books for general audiences, including Dinosaurs (Quercus, 2008), a ten-pound coffee-table tome, he shares these discoveries with dinosaur aficionados of all ages. “In a lot of ways, I see myself as a writer who uses fossils as a subject,” says Brusatte, who wrote for his local newspaper and amateur paleontology magazines during high school and college. His most recent book, Field Guide to Dinosaurs (Quercus, 2009), transports young readers on a dinosaur-spotting Mesozoic safari, complete with armored vehicles.
Real-life expeditions are not so well-equipped. On fossil digs in Wyoming, South Dakota, and other sparsely populated areas—the trips were part of Sereno’s Dinosaur Science course—he and other students would camp at the site, waking up with the sun and working all day. “Literally you’re sleeping right beside the bones,” says Brusatte, who went as a teaching assistant. For other explorations, hotels are the norm. This past summer, for example, he and colleagues traveled to Portugal to investigate a newly discovered site rich with fossils dating to the mass extinction that began the dinosaur age 200 million years ago. There, he says, “you’re looking in quarries and people’s backyards.”
Although he won’t return to the field until June—paleontologists typically hole up in their offices during fall and winter to work on manuscripts and analyze fossil finds—Brusatte has plenty to keep himself busy. “Every day is a challenge because you might have a new specimen come across your desk,” he says. “We’re the first people to really ever see these fantastic creatures that lived millions of years ago, and we have to figure out what they are on the simplest level.”