Fossils give look into history of Pembina Gorge

Some 80 million years ago, North Dakota was covered by three oceans with Caribbean-like, sub-tropical climates and a veritable cornucopia of plant and animal life.

Posted on 8/31/13

By Lee Coleman

Known as the Pierre Sea, the waterway was part of the western interior seaway during the Cretaceous Age.

Salmon-like fish, giant sea birds (Hesperornis), giant squid (Tuseothus), flying sea birds (Pterandon), tarpon-like fish (Ziphactinus) and sharks (similar to today’s tiger sharks) called the Pierre home.

Most notably, the ferocious Mosasaur, a giant marine reptile that grew to 35-40 feet, was considered the apex predator in the Pierre and was likened to the Tyrannosaurus Rex on land.

‘It is mind-boggling to think North Dakota was covered by oceans 80 million years ago but now, we are as far away from any oceans that we are going to get,” said Dr. John Hoganson, state paleontologist with the North Dakota Geological Survey. “Because the climate was warmer and there weren’t any icecaps, there was a lot more water in the oceans at that time.

“Ocean levels were much higher than today, in fact, they were so high, Florida, as an example, would have been completely underwater.”

According to Hoganson, a 32-year veteran paleontologist, the three oceans covered North Dakota for 15 million years and the last ocean to retreat from North Dakota was 60 million years ago. There hasn’t been any oceanic conditions since then.

The Pierre Sea, considered to be swallow with a depth of 500 feet, covered what we know as the Pembina Gorge in Walhalla.

After the last ocean retreat, fossils of plant and animal life were left behind and since 2000, Dr. Hoganson has brought teams into the gorge to search for evidence of marine life.

Last week, a scientific, professionally conducted fossil excavation, co-sponsored by the North Dakota Geological Survey, the North Dakota Parks and Recreation Department and Walhalla Economic Development, took place for the public on a hillside in the gorge.

“It went really well,” said Hoganson. “This was one of our public fossil digs we do every year. We’ve had about 100 people out here and we’re finding the remains of fish, large sea birds and mosasaurs.

“Last year, we found the fairly complete skeleton of the mosasaurs right where we’re standing. We extracted about 98 vertebrae.”

This year, seven more vertebrae of the specimen have been found in the same area and paleontologist Jeff Person of the Geological Survey estimated the mosasaur was about 35 feet long.

“We have had good luck with this dig so far,” Person said. “We’ve found a lot of fish, bird bones and the other vertebrae of the mosasaur.”

Although many theories try and suggest what happened to the oceans and caused the extinction of three-quarters of life on earth, Hoganson said the KT Boundary Extinction Theory holds the most credence.

“It was an extinction event that wiped out all the dinosaurs and ocean animals,” he explained. “65 million years ago, the creatures we find remains of here were extinct.

“It was a huge biological disaster. The most accepted theory that caused the extinction is the asteroid impact theory.”

The theory suggests an asteroid hit the earth and disrupted the climate. The impact crater would have been six miles in diameter and 100 miles across and that crater has been identified in the Yucatan area of Mexico.

“Most scientists believe the explosion blew all of this material in the air that altered the climates and wiped out all the animals.” Hoganson noted.

Hoganson said all fossil discoveries, whether large or small, are significant.

“Every new discovery is important,” he explained. “Every new species discovered is very important from a scientific standpoint to learn more about what life was like in the past.

“Only one-tenth of one percent of all life that lived on earth became fossilized.

“That means we have no record of 99.9 percent of all plants and animals that lived on earth.”