It was a creature without competitors. Even now, long-vanished, it remains dominant – at least in the human imagination.
Tyrannosaurus Rex was a 15,000-pound predator of almost unimaginable power. It flourished in the few million years before the extinction event that decimated its kind. And though it’s certainly the most famous dinosaur, much about T-Rex, and its broader tyrannosaur lineage, remain a mystery.
Now, scientists are taking a fresh look at tyrannosaur fossils from Big Bend National Park. Their work could shed new light on these indelible ancient animals.
That’s Dr. Thomas Adams is the paleontologist at San Antonio’s Witte Museum.
“Every time I talk to a young person who says, ‘I want to be a paleontologist when I grow up,’ it's like, ‘Oh, great! What do you want to do?’ And they say, ‘Well, I want to study T-Rex,’” Adams said.
The T-Rex fascination has borne fruit, he said. In their obsessive hunt, paleontologists have discovered 30 T-Rex skeletons, mostly on the northern Great Plains, from Colorado to Saskatchewan.
Texas, on the other hand, has been slim pickings, with the exception of Big Bend. Here, tectonic forces have exposed rocks from the Late Cretaceous Period, the end of the Dinosaur Age. In 1970, paleontologists found the maxilla — or upper jawbone — of a tyrannosaur. And in 2002 and 2009, they recovered parts of a tyrannosaur leg and foot. The latter were on display at Dallas’s Perot Museum of Nature and Science – until Adams and his colleagues decided to take a closer look.
“It's been on exhibit that entire time,” Adams said, “but has never been studied. I realized: Here's an opportunity. We should probably look at this because it's the most complete tyrannosaur material we have for Texas.”
The fossils are unusual. They’re 25 percent smaller than adult T-Rex fossils in the north. And they’re older — dating to about 69 million years, as opposed to 66 or 67 millions years.
The tyrannosaur lineage endured for a hundred million years. Early tyrannosaurs were mid-sized predators. The immense T-Rex was the family’s last hurrah.
So – are the Big Bend fossils those of a young T-Rex? Or do they represent an older, previously unknown member of the tyrannosaur family?
“In Big Bend in the latest Cretaceous, is T-Rex there and is it represented by these not fully grown individuals?” Adams said. “Or do we have a smaller tyrannosaur in the south? And that's the question that we're trying to discover through the different kinds of analysis we're conducting.”
One kind of analysis involves bone “histology.” Like trees, bones add rings each year of their growth. A T-Rex reached maturity at about 17. If the Big Bend tyrannosaur was, say, 14, it could plausibly have been an adolescent T. Rex. Adams is also using 3-D modeling to make detailed measurements of the fossils, for comparison with other examples.
The Big Bend fossils have another striking feature — the foot bone is marked by four parallel grooves.
“Based off the size of them, the only thing that could make these particular bite marks was probably an animal of similar size or bigger.,” Adams said. “So we know that this individual had been chewed on by a tyrannosaur.”
As part of their work, the team returned to the site of the Big Bend tyrannosaur discoveries, in hopes of finding more. They came up empty. But they aren’t done.
“We have other fossil localities in the park that we are hoping to be able to return to and find more things and hopefully make more discoveries, including tyrannosaurs,” Adams said. “There's still a lot to be discovered. Every new fossil we find changes things.”
With luck, Big Bend will yield new insights into the most charismatic of dinosaurs.
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