One glaring omission plaguing the widely accepted Cretaceous-Paleogene (K-Pg) extinction event caused by a massive asteroid impact 66 million years ago that wiped out all non-avian dinosaurs is the paucity of mass graves proving this catastrophe.

Among the first fossil evidence for the instantaneous die-off of diverse animals was found in a soil layer only 10 cm (3.9 inches) thick in New Jersey some 5,000 km from the impact site off the Yucatan Peninsula in Mexico, indicating the death and quick burial of these animals. This site showed that burial under debris occurred suddenly and quickly over wide distances on land.

A team of paleontologists from the University of Kansas say they’ve discovered a "mother lode of exquisitely preserved animal and fish fossils" at the Tanis exploration site in North Dakota. They presented their findings in a paper published Monday in the Proceedings of the Academy of Natural Sciences.

Scientists agree the Chicxulub asteroid's impact was the most cataclysmic event ever known to have befallen the Earth. This global cataclysm eliminated 75 percent of our planet's animal and plant species, extinguishing the dinosaurs and paving the way for the rise of homo sapiens or the modern human race.

Researchers contend the asteroid impact ignited rapidly spreading, seismic surges that triggered a sudden, massive tsunami and debris from an arm of an inland sea known as the Western Interior Seaway.

At the Tanis site’s Hell Creek Formation, this surge left "a tangled mass of freshwater fish, terrestrial vertebrates, trees, branches, logs, marine ammonites and other marine creatures," according to Robert DePalma, the study’s lead author and a graduate student and curator of the Palm Beach Museum of Natural History in Florida.

The fossils were packed into a "rapidly emplaced high-energy onshore surge deposit" along the KT boundary that contained associated ejecta and iridium impactite associated with the impact about 66 million years ago.”

The study said some of the fish fossils were found to have inhaled "ejecta" associated with the Chicxulub event, suggesting seismic surges reached North Dakota within "tens of minutes," said DePalma.

"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," he said. DePalma and his colleagues describe the rushing wave that shattered the Tanis site as a "seiche."

Study co-author David Burnham noted that the sedimentation appeared to have happened instantaneously that all the fossils were not crushed but were preserved in three dimensions.

"It's like an avalanche that collapses almost like a liquid, then sets like concrete. They were killed pretty suddenly because of the violence of that water. We have one fish that hit a tree and was broken in half."

The fossils at Tanis include what were believed to be several newly identified fish species. Other fossils were "the best examples of their kind," DePalma said, adding that no other site boasts of such a gargantuan record like this.

"And this particular event is tied directly to all of us -- to every mammal on Earth, in fact. Because this is essentially where we inherited the planet. Nothing was the same after that impact. It became a planet of mammals rather than a planet of dinosaurs."

RELATED STORIES