March 24, 2019

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Tyrannosaurus Rex: The Once and Future King

Tyrannosaurus Rex: The Once and Future King
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The king is dead. Long live the king!

Tyrannosaurus rex is still the biggest, baddest land predator of all time. It was the size of a city bus, with a head almost as long as Tom Cruise is tall and a smile every bit as devastating. Scientists are just as smitten as the rest of us.

After T. rex was first described in 1905, the world’s most charismatic megafossil could have turned out to be a mere curiosity. There was no guarantee more would be found, nor could anyone anticipate how interesting its history would turn out to be. But for more than 100 years, T. rex has been an extraordinary gift to the study of dinosaurs, and perhaps to science in general.

Recently, the pace of discovery has quickened, and many of the findings about T. rex, the other tyrannosaurs who were its relatives and the prehistoric lives they led will be celebrated with “T. Rex: The Ultimate Predator,” a new exhibit opening March 11 at the American Museum of Natural History in New York.

In June, the Smithsonian National Museum of Natural History in Washington will reopen its hall of fossils, crowned in glory with its own T. rex in a new stance.

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The curators of the exhibit in New York are two longtime researchers on T. rex and other dinosaurs: Mark Norell, the curator of fossil amphibians, reptiles and birds at the museum; and Gregory Erickson, a paleobiologist at Florida State University.

In a joint interview, they were insistent that T. rex is far more than just a pretty, horrifyingly scary face. It’s an astonishing evolutionary achievement and a scientific star.

Dr. Norell said T. rex has helped foster a surge in dinosaur paleontology over the last 20 years, evident in the rising number of researchers and new fossils, and in the increasing sophistication of techniques to study the finds.

“In the last 30 years, the number of tyrannosaurs has increased threefold,” he said. In terms of technology, “it’s a different world.”

Dr. Erickson added: “The golden age of paleontology is right now.”

Other researchers, like Philip J. Currie, a dinosaur paleobiologist at the University of Alberta in Canada, agreed that the field has exploded. “More is going on now than ever,” he said. When he started in the 1970s, “there were probably only six of us in the world who were paid” specifically to study dinosaurs.

Others taught vertebrate anatomy or biology, or were dedicated amateurs. “Right now, there’s maybe 150,” he said, not to mention a “colossal increase in the number of scientific papers.”

From the time it was discovered, T. rex has been a sensation, attracting both the public and researchers. Each new skeleton or partial skeleton was hailed.

Some, like the T. rex skeleton named Sue, which now stands in the Field Museum in Chicago, attracted international attention. Sue was found in 1990, the biggest and most complete T. rex skeleton ever. The museum paid $8.3 million dollars for it.

The reconstruction of another giant found shortly after Sue, known as Scotty, will be unveiled at the Royal Saskatchewan Museum in Regina in May. Perhaps the name of the town will prompt overdue questions about why the great dinosaur was not named Tyrannosaurus regina.

It’s not because all the specimens found so far are male. There is no consensus on what sex they are, because it’s just not that easy to tell — particularly if all you’ve got is a skull or a thigh.

Few finds are 90 percent intact, as Sue was (named for her discoverer, Sue Hendrickson). One T. rex so far was found to have a kind of bone that was said to clearly identify it as female. But even that result is controversial.

Studies using CT scans, chemical analyses and new microscopic techniques have also illuminated the behavior, evolution and sensory abilities of T. rex itself.

Investigations of where and how muscle attached to the skull showed that its jaw had a bite strength of 7,800 pounds, enough to cleave the bones of other massive dinosaurs. Coprolites, fossilized feces, showed the presence of partly digested bones, indicating that it had the stomach juices to cope with them.

Dr. Erickson did microscopic studies of bone growth rings, which led to a determination of how old individual dinosaurs were and how fast they grew. T. rex apparently put on about five pounds a day in its teenage years. It lived to 30 at most. It was, as Dr. Erickson describes it, “the James Dean of dinosaurs. Live fast, die young.”

For a while, there was a lively debate about whether T. rex was more like a vulture than a hawk, too awkwardly built to chase down and kill prey. Healed bite marks on other dinosaur fossils, and a T. rex tooth embedded in the tail of an duckbill dinosaur, indicate that T. rex did hunt other dinosaurs, although it probably also scavenged, as most predators do.

Judging by its relatives, and by fossilized footprints of a group of the dinosaurs together, T. rex was a social animal. It probably hunted in groups, certainly when it was younger. Its behavior probably changed as it grew. When it was only half the length of a bus, it likely ran a lot faster than when it was full grown.

The dinosaur’s brain was big even for its size, suggesting higher intelligence than other dinosaurs. It had great vision, with the eyes moved forward on its skull for good depth perception. Its ears were adapted for hearing low frequency sounds. Its brain case suggests T. rex’s olfactory abilities were superb, even though a good sense of smell was probably rare in dinosaurs.

And it had feathers, more when it was young, but probably a tail plume, at least, at maturity. No T. rex fossil has been found that shows the presence of feathers but, said Dr. Norell, given what we know about other tyrannosaurs, related dinosaurs and the course of dinosaur evolution, “We have as much evidence that T. rex had feathers as we do that Neanderthals had hair.”

How T. rex came to be, and what its relatives were like, is at the heart of both the exhibit in New York and recent science. T. rex is just one species among many. The superfamily that contains the tyrannosaurs includes more than two dozen other dinosaurs. They date back to 100 million years before T. rex lived.

“It took evolution a long time to make T. rex,” said Stephen Brusatte, a paleontologist at the University of Edinburgh and author of a recent book on dinosaurs.

Most of the early tyrannosaurs were small, some as small as a chicken. Many were dog-size to deer-size. (Just last week, a smallish tyrannosaur from North America was reported.) These earlier tyrannosaurs were not the top predators for most of those 100 million years.

“For most of the time, they were second- or even third-tier predators,” Dr. Brusatte said. “For most of their history, tyrannosaurs weren’t that special.”

And then T. rex emerged near the very end of the age of the dinosaurs, becoming the dominant predator in North America.

The rise of T. rex is a lesson in how evolution works, Dr. Brusatte said: with no preordained plan. Over the millenniums, many predatory dinosaurs appeared and disappeared. The tyrannosaurs were successful, and over time evolved.

But if other large dinosaurs like allosaurus hadn’t gone extinct, there might not have been room at the top of the food chain for a creature like T. rex.

It could be said that T. rex lucked out. But then, it ruled at the very time 65 million years ago when all the non-avian dinosaurs went extinct.

Envy always follows royalty. And Dr. Brusatte said there is some resentment that T. rex draws so much attention and so many paleontologists.

“People who study non-dinosaurs say dinosaurs get all the attention,” he said. “People who study dinosaurs say theropods get all the attention. People who study theropods, say, oh, tyrannosaurs get all the attention.”

And among tyrannosaurs, there is only one star, the king. But there’s a reason T. rex gets so much attention.

“It deserves it,” Dr. Currie said.



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