Tuesday, July 6, 2010

Dromaeosaurus albertensis


Dromaeosaurus albertensis, originally uploaded by mcwetboy.
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A young boy's intense gaze over the exhibit railing at the National Geographic Society's Explorers Hall captured what everyone in the room seemed to feel - a sense of awe.

They were staring at rows of blade-shaped teeth, eye sockets big enough to push a fist through, and the sleek, 5-foot-long jaw of a dinosaur.

"I sure wouldn't want to be caught by one of those if I was roaming the plains 65 million years ago," said Reg Murphy, president of the society, as the "Africa's Dinosaur Castaways" fossil exhibit opened at the Northwest museum. It will run until Sept. 8.

He was referring to the displayed replica of the recently excavated skull of Carcharodontosaurus, or "shark-toothed reptile," one of two major finds uncovered by the team of University of Chicago paleontologist Paul Sereno during an expedition to Saharan Morocco last summer.

"Carcharodontosaurus was the largest predator during the period from 65 million to 100 million years ago in Africa and probably preyed on plant-eating sauropods," Mr. Sereno said.

The dinosaur was discovered at the turn of the century by German scientist Ernst Stromer, Mr. Sereno explained, and "it rivaled Tyrannosaurus rex in both size and ferocity, but had a much smaller brain than its North American counterpart."

Mr. Sereno, 38, said these fossil discoveries shed light on the final chapter of dinosaur evolution on the isolated continent of Africa. "The pieces we found paint a picture of Africa's dinosaurs different from those on any other continent at the time," he said.

The earliest dinosaurs and their Jurassic descendants that lived more than 150 million years ago looked remarkably alike worldwide. But by the time Carcharodontosaurus appeared about 90 million years ago, the Earth's land had become a patchwork of separate continents.

The team's discoveries - bones differing from those of similar species found in other parts of the world - suggest that, once isolated, dinosaurs in Africa and other continents embarked on divergent evolutionary paths.

These finds, once embedded in sandstone, also provide evidence that today's Sahara Desert once was a flood plain similar to the Mississippi Delta, with flowing rivers edged by coniferous trees, said Mr. Sereno, whose team discovered nearly 50 different animal species.

Along with the enormous skull of the largest terrestrial animal ever to roam the Earth, a member of Mr. Sereno's team - a young assistant who was along to record findings and later provide educational outreach - stumbled upon the skeleton of a dinosaur never before known to exist.

Deltadromeus, or "delta runner," coexisted in the same environment as the Carcharodontosaurus, Mr. Sereno said.

Experts believe it was a speedy hunter with extraordinarily delicate and long limbs. (The exhibit reproduction stretches more than 25 feet.) Mr. Sereno declined to estimate how fast the dinosaur would have run, saying only that the beast "could not outrun a horse, but could certainly outrun a human."

Gabrielle Lyon, 24, the discoverer of the set of bones, said she found the fossils when she took a goat path to the bottom of a rough cliff instead of the steeper, more dangerous route taken by other team members.

"My eye caught a jewel shining up from what turned out to be a dinosaur bone," she said. She continued digging, finding parts of arms, legs, tailbone vertabrae and the chest bone of the same skeleton.

The moment was long overdue. The group had endured relentless extreme conditions for 41 days with only moderate success in recovering fossilized remains.

The trip was intended to help explain dinosaur evolution in Africa, a continent rarely visited for fossil digs. The last fossil evidence discovered in Saharan Morocco was a few Carcharodontosaurus bones uncovered by Stromer. Those bones were destroyed during World War II.

"Almost everything we know is from dinosaurs in North America. We needed information from all the other continents," Miss Lyon said. "We were the first team to try and develop an accurate picture of dinosaur life 90 million years ago."

A core team of about eight scientists, students and assistants was assembled from the University of Chicago and Morocco. The group set out in April 1995 for London, where they rode in land rovers and ferries until they reached the Kem Kem wilderness near Taouz in southwest Morocco.

Days began about 5 a.m. with drives to rock formations within a 100-square-mile area, looking for signs of embedded fossils. When someone spotted the edge of a tooth or a crab traced in sandstone, the group would begin chipping away at rock and sifting through sand and dirt in the Saharan heat.

While scaling the rocky slopes of the Atlas Mountains in 120-degree heat to uncover the bones, many expedition members lost 20 pounds each in the first month. Rubble-strewn inclines tore up their boots, which had to be patched with strips from truck tires.

"It was one of the single most grueling experiences I can think of. The formation was so rough working on cliffs," Miss Lyon said. "One time, we even had to have one of our guys take a jackhammer up a cliff. And then there was the gas for it and the bits for the end."

The team would often work until midnight for about 10 days at a time before returning to a base camp at the edge of the desert to restock supplies.

Miss Lyon's discovery contrasts with the hundreds of isolated, smaller fossils found, she said. Mr. Sereno discovered the Carcharodontosaurus skull a few days later, just before the expedition was to end.

The exhibit at the museum is enhanced by a second model of the Carcharodontosaurus, which was given muscles, nerves, veins and skin by Canadian paleo-sculptor Garfield Minott. This scientific re-creation gives viewers the chance to get a close-up view of what the carnivore might have looked like as he sized up a human-sized meal.

***** WHAT: "Africa's Dinosaur Castaways"

WHEN: 9 a.m. to 5 p.m. Mondays through Saturdays, 10 a.m. to 5 p.m. Sundays, through Sept. 8

WHERE: National Geographic Society's Explorers Hall, 1145 17th St. NW


PHONE: 202/857-7588

Source Citation
Mizejewski, Gerald. "A fossil exhibit with real teeth: Dinosaur bones tell unique tale." Washington Times 27 July 1996: 1. Popular Magazines. Web. 6 July 2010.
Document URL

Gale Document Number:CJ56832357

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