Carnegie Museum of Natural History reflects the latest discoveries by incorporating them into its exhibits and programs. Gone is the old, scientifically incorrect T.rex wall painting in Dinosaur Hall, replaced by an accurate and visually stunning mural nearby. The hall features a dramatic sound and light show every hour, a robotic tour guide, and interactive computer games. You can examine a fossil that flew aboard the space shuttle in 1998, watch scientists extract fossils from a bed of rock, and see a replica of the largest flying animal ever known to exist. In March, a world-renowned scientist speaks about the end of the dinosaur era, and this summer we’re installing a life-sized model of Diplodocus on Forbes Avenue. This is the place where dinosaurs come back to life.

Walter Alvarez Explains the “Crater of Doom”
-Free Lecture March 8 in Carnegie Lecture Hall-
 It’s been over a century since scientists uncovered the evidence that dinosaurs ruled the animal kingdom during the Mesozoic era, and we’ve been fascinated ever since. But what happened to the dinosaurs? Why did they disappear?

 In the early 1990s, scientists announced a startling theory: Dinosaurs, and many other life forms, perished as a result of a giant asteroid that crashed into the Earth 65 million years ago.

 Geologist Walter Alvarez was at the forefront of the research that led to this astounding theory. Over the course of two decades, Alvarez pursued the question of the dinosaurs’ demise, making discoveries of his own and synthesizing those of other scientists. His theory is this: 
The asteroid’s impact, packing a wallop equal to that of 100 million hydrogen bombs, ripped apart whole forests, and it shook the surrounding land so violently that huge submarine landslides and giant tsunami resulted. Most of North America was reduced to a desolate wasteland within hours, but the other continents were not spared for long. The cloud of roiling debris that the impact produced blackened the sky for months all around the world, leading to a collapse of the food chain and the eventual death of most Mesozoic life forms, including the dinosaurs.
How does a scientist prove such a scenario? It wasn’t easy. The 20-year struggle to piece it together included searching for signs of iridium produced by the asteroid’s impact; chasing down leads that eventually proved incorrect; deflecting skeptics; a 10-year search for the impact crater; questions of oceanic or continental impact, decisions about one or multiple craters, or instant or gradual disaster.

But as compelling as it is, the Alvarez theory is not accepted in all scientific circles, especially among vertebrate paleontologists—scientists who study the fossil remains of animals with backbones, including dinosaurs.
“A great many vertebrate paleontologists accept the idea of a meteorite impact,” says Mary Dawson, curator of Vertebrate Paleontology at Carnegie Museum of Natural History. “But scientists are still not completely satisfied that this is the answer to why dinosaurs disappeared.” Reasons for this skepticism include the fact that many animals—including crocodiles, turtles and mammals--survived the impact, and perhaps dinosaurs could have as well. Also, many dinosaurs had died out before the end of the Mesozoic as part of the natural evolutionary process.

So why did the Mesozoic dinosaurs all die out around the same time? Dawson offers two theories: because of a climatic cooling (unrelated to the meteorite); or perhaps because of the proliferation of flowering plants, which have a different biological make-up than the plants herbivorous dinosaurs fed upon.
While no single theory on the end of the dinosaurs has yet been accepted as definitive, Alvarez’ “crater of doom” theory has “made a lot of scientists sharpen their skills in looking at that interval between the Mesozoic and the Cenozoic,” Dawson says. Don’t miss hearing one of the most renowned scientists—Walter Alvarez--explain his theory on March 8. The lecture is co-hosted by Carnegie Mellon University and Carnegie Museum of Natural History.
 

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New Mural Shows T.rex in a New Light

Some of these recent discoveries are reflected in the new mural in Dinosaur Hall, a dramatic color rendering by Michael Skrepnick, one of the most sought-after dinosaur artists in North America. In the Skrepnick mural, T.rex assumes the more horizontal posture that we now believe to be correct. 

“The horizontal posture is considered more accurate because new studies of the T.rex skeleton show this is how the bones fit together,” says Carnegie paleontologist Chris Beard. He says the biggest advance in showing that T.rex walked horizontally is the theory that theropods are related to birds. 

“The new posture of T.rex is not different from that of a blue jay at a bird feeder,” he adds.

Half a century ago, scientists didn’t know that theropods were related to birds, and they thought the bones fit together another way, resulting in a vertical stance. “That tells you there’s some flexibility” in thinking about various aspects of dinosaur biology, Beard says.

The natural surroundings of T.rex are on display as well, as the mural shows what scientists now believe to be an accurate portrayal of eastern Montana 66 million years ago. It was a sub-tropical coastal plain in those days, with an inland seaway called the Cannonball Sea that extended from the Gulf of Mexico up into Canada. Look closely and you’ll see something familiar--a pond turtle, the artist’s reminder that some dinosaur-era flora and fauna are still part of the Earth’s biodiversity today.
 

Largest Flying Reptile: Quetzalcoatlus 

Look for Our Dinosaur on Forbes Avenue

Called “Dippy” by Andrew Carnegie’s friends, Diplodocus has been the museum’s signature exhibit ever since Andrew Carnegie had the fossil bones that were discovered in Wyoming in 1899 delivered to Pittsburgh and mounted in his new museum. 

Carnegie enjoyed presenting casts of Diplodocus to museums around the world. He boasted about America’s scientific progress, and his own institution’s pre-eminence in research.  In 1904 he honored the King of England’s request to have one at the British Museum, and he kept on giving to presidents, kings and emperors, for installation in other national museums.  By 1913 he had given replicas to natural history museums in Germany, France, Austria, Italy, Spain, Russia and Argentina.  Mrs. Carnegie sent a replica to Mexico in 1930, and another set of cast bones was sent to Munich in 1934 (but not erected).  The casts were re-used to make molds for Dinosaur National Monument in Utah, but by then had reached the end of their useful life.  As far as we know, the fossil skeleton of “Dippy” is still a must-see exhibit in nine of the world’s greatest natural history museums.

Science now has new information about the behavior of Diplodocus.  “Dippy” is thought to be a browser of understory plants, so our replica’s neck will be more horizontal than before. The long tail probably balanced its long extended neck, and so the tail will be raised off the ground.  The bronze-colored giant who greets the public on Forbes Avenue will be the most lifelike Diplodocus science can create.     

--R. Jay Gangewere