A meteor impact 66 million years ago generated a tsunami-like wave in an inland sea that killed and buried fish, mammals, insects and a dinosaur, the first victims of Earth’s most recent mass extinction event.
Robert DePalma
A meteor impact 66 million years ago generated a tsunami-like wave in an inland sea that killed and buried fish, mammals, insects and a dinosaur, the first victims of Earth’s most recent mass extinction event. The deathbed created within an hour of the impact has been excavated at an unprecedented fossil site in North Dakota.

In a paper published April 1 in the Proceedings of the National Academy of Sciences an international team of authors, including University of Washington Provost Mark Richards, share the discovery of a site that tells another piece of the story from the day a meteor strike is thought to have led to the end of the dinosaurs.

“It’s like a museum of the end of the Cretaceous in a layer a meter and a half thick,” said Richards, who is also a professor in the UW Department of Earth & Space Sciences.

This unique fossilized graveyard – fish stacked one atop another mixed with burned tree trunks and conifer branches, dead mammals, a pterosaur egg, a mosasaur, insects, the carcass of a Triceratops, seaweed, and marine snails called ammonites – was unearthed over the past six years in the Hell Creek Formation in North Dakota by lead author Robert DePalma.

“This is the first mass death assemblage of large organisms anyone has found associated with the KT boundary,” said DePalma, curator of paleontology at the Palm Beach Museum of Natural History in Florida and a doctoral student at the University of Kansas. “Nowhere else on Earth can you find such a collection consisting of a large number of species representing different ages of organisms and different stages of life, all of which died at the same time, on the same day.”

The new study describes the site, dubbed Tanis, and the evidence connecting it with the asteroid or comet strike off Mexico’s Yucatan Peninsula. That impact created a huge crater, called Chicxulub, on the ocean floor and sent vaporized rock and cubic miles of asteroid dust into the atmosphere.

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