Fossil Discovery Marks Roots of Modern Animal : Evidence Found That Asteroid Hit, Caused Extinction

The largest fossil find in North America, more than 100,000 pieces of fossilized bone dating from a critical period in evolutionary history that marked “the emergence of the modern world of animals,” has been uncovered in Nova Scotia, scientists announced Wednesday.

The fossils, estimated to be more than 200 million years old, include 12 skulls and jaws from tritheledonts, the reptiles considered closest to mammals, in addition to other skulls, teeth, jaws and bones from dinosaurs, ancestral crocodiles, lizards, sharks and primitive fishes.

The scientists also found a series of dinosaur footprints about the size of a penny--the tiniest known anywhere, they said.

“It really did shock us, what we found,” said geologist Paul E. Olsen of Columbia University’s Lamont-Doherty Geological Observatory, who made the discovery last summer with biologist Neil H. Shubin of Harvard University.

Found in Minas Basin

The fossils were unearthed on the north shore of the Bay of Fundy’s Minas Basin, about six miles east of rural Parrsboro. The region is part of a rock formation known as the Newark Supergroup, which stretches from the Canadian province of Nova Scotia to South Carolina.

The field work was carried out in cooperation with the Nova Scotia Museum in Halifax and funded by the National Geographic Society, which made the announcement.

Olsen and Shubin described the era of their find as that of “a time of mass extinction” as well as “the emergence of the modern world.”

The fossils are believed to be from a time that comprised the “boundary” between the Triassic and Jurassic periods. Scientists believe that this is when reptiles were beginning to lose their dominance in the world and dinosaurs were beginning to emerge.

Dinosaurs Vanished

Dinosaurs dominated the Earth until they vanished about 65 million years ago. The Jurassic period ended 144 million years ago.

“This time period (between the Triassic and Jurassic eras) marked the emergence of the modern world of animals,” Shubin said. “It set the clock for the later evolution of all these groups. We found the most abundant quarry of this time period in the world.”

Olsen said that the creatures probably had survived a catastrophic extinction that occurred less than 500,000 years earlier. “This major event killed the old world and allowed the new world to arise,” he said.

Olsen theorized that the mass deaths were caused by an asteroid known to have struck the Earth 500 miles northwest of the excavation site, leaving a crater 40 miles in diameter. “Scientists at Berkeley have calculated that the energy released was 10,000 times that of all the Earth’s nuclear weapons going off at once,” Olsen said.

Fireball Blocked Sun

He said the ensuing fireball and debris would have blocked sunlight and destroyed the ecological balance of a large region, killing plants and animals. At least 43% of land and lake animals did not make it across the “boundary,” he added, and although new species arose, new families of animals did not.

Olsen and Shubin said that they would attempt to prove a connection between the asteroid’s impact and the fossils by searching for evidence of the asteroid within the material they found.

“Dating methods on the asteroid are imprecise,” Olsen said. “We need to find some direct evidence within the rocks themselves, or remnants of the asteroid itself.”

The two scientists said they hope the abundance of tritheledont skulls and jaws will clarify unanswered evolutionary questions about mammals.

New Anatomy Parts

“We are finding new parts of the anatomy that weren’t known before,” Shubin said. “This may help us determine what a primitive mammal is compared to an advanced reptile.”

The scientists said they expected their discovery to open up new fossil-hunting grounds on the East Coast, which originally had been thought to be a meager source of fossils. The sedimentary rocks of the Newark Supergroup, believed to be 175 million to 225 million years old, traditionally had been neglected by scientists who concentrated their exploration in the southwest United States, Africa and Asia.