Fossilized snapshot of mass death found on North Dakota ranch
BOWMAN, N.D. — Robert DePalma was heading to a known fossil bed when he got a tip that persuaded him to take a detour to a cattle ranch near this southwestern North Dakota community where he would make a stunning scientific discovery.
DePalma, a doctoral student in paleontology, surveyed the site, which recently had been abandoned by a private fossil collector who found some fish fossils that crumble easily, an unpromising site for salable specimens.
Initially, DePalma was disappointed when he arrived at a gray-domed outcropping in the remote pasture. But as he began shoveling, his trained eye spied grayish-white specks in layers of soil — tiny beads of glass formed by molten rock.
Not just any molten rock, but a variety that was blasted into the air by an asteroid impact. The site seemed to have millions of the tiny glass balls.
Intrigued, DePalma kept digging, and found a dazzling assortment of fossils, very delicate yet wonderfully preserved. He found a jumble of wood, cypress tree bundles, tree trunks coated with amber and fish, all entombed together in muddy sediment that hardened over the eons into mudstone.
DePalma’s field assistant, Rudy Pascucci, was with him as he began to tease out the story the tangled fossils told.
Oddly, he realized that he found both freshwater and saltwater fish species in the layer of earth he was examining. As he continued to work the site, DePalma concluded that he would be able to safely remove complete fish if he did so painstakingly.
He decided the site was valuable, so agreed to pay the rancher for the right to work the site, which the private collector had personally shown him in July 2012.
DePalma, later joined by a series of leading scientists, since has returned to the fossil site near Bowman many times.
His team has determined that the jumble of fossilized plants and animals were deposited there by a surge of an ancient inland ocean — all washed up in the minutes or hours after a huge asteroid struck Earth, landing eons ago in Mexico's Yucatan Peninsula.
DePalma had found a fossilized snapshot of mass death that recorded the extinction of the dinosaurs 66 million years ago.
The team's work was published online Monday, April 1, in the prestigious Proceedings of the National Academy of Sciences in a paper titled, “A seismically induced onshore surge deposit at the KPg boundary, North Dakota.”
The K-Pg boundary, formerly called the K-T boundary, is scientific shorthand for the cretaceous-paleogene boundary, the layer of sediment that recorded the extinction of dinosaurs and most other life on Earth as a result of the catastrophic asteroid strike.
In other words, in a cow pasture near Bowman in southwestern North Dakota, DePalma had found a geological snapshot of the day the dinosaurs died.
An interesting site
Rudy Pascucci was along with DePalma when he made the fateful decision to visit the cattle ranch near Bowman instead of driving to an established fossil bed in Harding County, South Dakota.
“The site was known to paleontologists,” Pascucci said. “We weren’t the first to work at this particular site.”
He added: “We thought we were going there for a week. Interesting site with some dead fish.”
It turned out to be a paleontological blockbuster find. “We spent the entire summer there.”
Pascucci serves as DePalma’s field assistant. He’s also director of the Palm Beach Museum of Natural History in Wellington, Florida, where DePalma, who is a graduate student at the University of Kansas, does much of his lab work.
DePalma was impressed to see that the fossilized fish were so well preserved. “They were almost 3D,” much better than the smashed specimens that commonly are found, Pascucci said.
DePalma, whose obsession with paleontology began in high school, was able to extract clues from the layer of rock that would elude even some specialists, Pascucci said.
“He’s an amazing paleontologist,” he said. “His power of observation was an amazing thing to behold.”
In South Dakota, DePalma has made earlier significant discoveries, including a dinosaur called Dakotaraptor and proof that T-rex was a predator species, not merely a scavenger as some researchers believed, Pascucci said.
The K-T boundary in the buttes around Bowman is easy to spot, a black band located near the surface in outcroppings.
Soon after their arrival at the site, “Robert noticed we were very close to that K-T boundary” — an indication that, in terms of geological layers, they were very close to the extinction of the dinosaurs.
Clues suggested death came quickly to the fish, many with their mouths agape, suggesting they died while trying to breathe, their gills clogged by the asteroid debris.
“Timing of the incoming ejecta spherules” — molten rock material emitted by the asteroid strike — “matched the calculated arrival times of seismic waves from the impact, suggesting that the impact could very well have triggered the surge,” DePalma said in a statement published by the University of Kansas.
The fossil site near Bowman, which DePalma calls Tanis, a reference to a lost Egyptian city, demonstrates how extinctions could occur rapidly even thousands of miles from the asteroid crash site.
“A tsunami would have taken at least 17 or more hours to reach the site from the crater, but seismic waves — and a subsequent surge — would have reached it in tens of minutes,” DePalma said in the statement.
'This is the day'
The theory that a giant asteroid killed off the dinosaurs was first advanced in the 1980s by a pair of father-and-son scientists, Walter and Luis Alvarez.
They were the first to conclude that a thin band of rock provided evidence of the killer asteroid since it contained high levels of iridium, a mineral that is common in other astronomical bodies but rare on Earth.
But until DePalma and his team came along, nobody had found significant dinosaur remains within the telltale rock boundary.
“You’re going back to the day that the dinosaurs died,” Timothy Bralower, a Pennsylvania State University professor, said of the North Dakota discovery. “That’s what this is. This is the day the dinosaurs died.”
It is exceedingly rare to find in the fossil record evidence of a single event like the cataclysmic asteroid strike, which triggered fires within 1,500 miles of the impact and caused a fiery plume to rise up halfway to the moon, according to computer models.
The fires consumed an estimated 70 percent of the world’s forests, and caused giant tsunamis across the Gulf of Mexico, so forceful that they shoved debris far inland before the wave withdrew deep into the ocean.
At the time, western North Dakota was a tropical expanse of cypress swamps, meandering rivers draining the Rocky Mountains, then uplifting, and fertile deltas.
Today it’s known as the Hell Creek Formation, badlands terrain that covers parts of western North Dakota, western South Dakota, Montana and Wyoming. It contains some of the richest fossil beds of the Cretaceous era, millions of years culminating in the extinction of the dinosaurs.
The Bowman region is one of the areas around North Dakota where paleontologists have been actively excavating fossils for years.
Other important discoveries have been made around Bowman, according to Dean Pearson, director of the paleontology section of the Pioneer Trails Museum in Bowman, and an amateur paleontologist.
For example, at a location near Marmarth, N.D., in Slope County and another in Bowman County, researchers have found the tiny glass beads similar to those found at DePalma’s site. Also, elsewhere in Bowman County, a triceratops dinosaur bone was found roughly a foot below the K-T boundary, discovered by a team Pearson assisted.
“The area here does preserve quite well that particular time, which is when the dinosaurs went extinct,” he said.
As for DePalma’s discovery, which came from a site Pearson has not visited, “I think it’s a big deal for the area,” he said. “I expect there to be follow-up, at least for the short-term if not the long-term.”
Clint Boyd, senior paleontologist for the North Dakota Geological Survey, had not yet read the scientific study reporting DePalma’s find.
“It’s always been plausible that somebody could find a site like this,” he said. “Studies like this point out the great research potential here in North Dakota.”
It likely will take years to continue analyzing the treasure trove being unearthed in the cow pasture, and Pascucci believes DePalma and colleagues will continue to explore the site.
“It has been very carefully researched,” and vetted by specialists, Pascucci said of the findings. One of the co-authors on the study is Walter Alvarez, who first connected the K-T boundary to the dinosaurs’ extinction. “This has been carefully, carefully, carefully researched.”