How Tyrannosaurs Grew from Tiny "Jackals" to Ferocious Giants

By Andrew Moseman | September 17, 2010 11:01 am

TRexTyrannosaurus—the name brings to mind the towering T. rex with its giant teeth and tiny arms, hunting humans in Jurassic Park or standing reconstructed in the natural history museum. This king predator dominates our imaginations, and because of that it is the most heavily studied dinosaur there is. In the last decade, and even in the last year, new studies have shown us that T. rex‘s lineage stretches back to Tyrannosaurus ancestors that stood no taller than us for nearly 100 million years. In the journal Science this week, paleontologists lay out all the recent discoveries that reveal the story of the world’s favorite ancient monster.

Stephen Brusatte of the American Museum of Natural History in New York, one of the study leaders, says:

“Up until about ten years ago we only knew about T. rex and a handful of its closest relatives — all colossal, apex predators from the end Cretaceous in North America,” Brusatte explained. “Now we know of about 20 tyrannosaur species that span a time period of 100 million years, most of which are very small.” [MSNBC]

Indeed, just in the last year scientists have discovered six new species. The team writes in the study that one of those newly discovered species was “100 million years older and 1/100 the size of T. rex.”

University of Maryland tyrannosaur expert Thomas Holtz, Jr., added: “I like to call [early tyrannosaurs] the jackals of the Jurassic and Early Cretaceous. “They were tough little guys, but they were little guys, sort of hanging out in the wings and taking out young dinosaurs and small dinosaurs but leaving the big prey to things like Allosaurus,” said Holtz, who was not involved in the new review. [National Geographic]

T. rex showed up late and burned out fast. Tyrannosaurs, for the first about 80 to 85 million years of their existence, grew no larger than a modern-day human. About 80 million years ago these dinosaurs hit a growth spurt, perhaps because giant competitors died off, and the great dinky-armed predator emerged. Because the worldwide dinosaur extinction event happened 65 million years ago, T. rex had a short run compared to its Tyrannosaur ancestors.

According to Mark Norell, another member of the study team, the flood of new Tyrannosaurus knowledge isn’t limited to finding new species.

Biologists who study the biomechanics of elephants or chemists who study proteins in bone have turned their attention to T. rex fossils. They’ve refined its posture. They’ve determined the length of its adolescence — 10 to 15 years — and its rate of growth — as much as 5 pounds a day. They also may have found remains of T. rex tissue, though that’s still in question. “What I find really interesting is what you can do with sort of an eclectic and diverse group of scientists all focused on one animal,” says Norell. [NPR]

If you’ve got Friday dino fever, Norell also co-wrote the DISCOVER feature “The Bone Collector,” on T. rex fossil hunter—and philanderer, and spy—Barnum Brown.

Related Content:
DISCOVER: The Bone Collector
DISCOVER: Destination Science: Hunting Dinosaurs with Jack Horner
DISCOVER: Dino Hunter, on paleontologist Phil Currie
80beats: T. Rex May Have Been a Hot-Blooded, Sweaty Beast
80beats: Miniature T. Rex Was a Man-Sized Monster

Image: Brusatte et. al / Science

  • Rhacodactylus

    I will pay any amount of money to get a T-Rex small enough that he can live in my house . . . get to work geneticists!

  • Crow

    A T-Rex your size would have you for a meal so fast it wouldn’t even be funny.

    Not that carnosaurs couldn’t be funny, of course …


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