Fossils from the day the dinosaurs died

66 million years ago an asteroid that was several miles in size impacted near the Gulf of Mexico in Chicxulub. The consequence for everything living was utterly devastating, we can see fossils for everything that thrived below the KT boundary and observe that it is all gone above that layer.

That was a day that had planet-wide consequences.

What is new, and this is very big news, is that a relatively unknown PhD candidate named Robert DePalma has found a massive fossil deposit that was was laid down on the actual impact day.

A seismically induced onshore surge deposit at the KPg boundary, North Dakota

He has published what will no doubt be the first of many papers that describes the insights gained from the newly discovered find at Tanis in North Dakota. The initial paper just published explains …

Emplaced immediately (minutes to hours) after impact, Tanis provides a postimpact “snapshot,” including ejecta accretion and faunal mass death, advancing our understanding of the immediate effects of the Chicxulub impact. Moreover, we demonstrate that the depositional event, calculated to have coincided with the arrival of seismic waves from Chicxulub, likely resulted from a seismically coupled local seiche.

The Tanis site is quite literally the moment of impact, and for a paleontologist, that’s a huge deal.

Finding palaeontology gold

The actual discovery was quite accidental. Within a very comprehensive article published in the New Yorker we learn how it all came about …

In 2012, while looking for a new pond deposit, he heard that a private collector had stumbled upon an unusual site on a cattle ranch near Bowman, North Dakota. (Much of the Hell Creek land is privately owned, and ranchers will sell digging rights to whoever will pay decent money, paleontologists and commercial fossil collectors alike.) The collector felt that the site, a three-foot-deep layer exposed at the surface, was a bust: it was packed with fish fossils, but they were so delicate that they crumbled into tiny flakes as soon as they met the air. The fish were encased in layers of damp, cracked mud and sand that had never solidified; it was so soft that it could be dug with a shovel or pulled apart by hand. In July, 2012, the collector showed DePalma the site and told him that he was welcome to it.

“I was immediately very disappointed,” DePalma told me.

It might be tempting to put it all down to bold luck. What perhaps needs to be appreciated is that DePalma had the skills and insight to truly appreciate what this was. As he worked at the site, there was a growing realisation …

…as soon as DePalma started digging he noticed grayish-white specks in the layers which looked like grains of sand but which, under a hand lens, proved to be tiny spheres and elongated droplets. “I think, Holy shit, these look like microtektites!”…

…As he dug, the momentousness of what he had come across slowly dawned on him. If the site was what he hoped, he had made the most important paleontological discovery of the new century….

… “When I saw that, I knew this wasn’t just any flood deposit,” DePalma said. “We weren’t just near the KT boundary—this whole site is the KT boundary!” From surveying and mapping the layers, DePalma hypothesized that a massive inland surge of water flooded a river valley and filled the low-lying area where we now stood, perhaps as a result of the KT-impact tsunami, which had roared across the proto-Gulf and up the Western Interior Seaway….

DePalma is quite a character

Stepping sideways, DePalma is indeed, to use that turn of phrase, “a character”. What is truly fascinating here is that not only is the discovery itself unique, the guy who made the discovery is also rather unique …

…DePalma pulled up to my hotel in a Toyota 4Runner, its stereo blasting the theme to “Raiders of the Lost Ark.” He wore a coarse cotton work shirt, cargo pants with canvas suspenders, and a suède cowboy hat with the left brim snapped up. His face was tanned from long days in the sun and he had a five-day-old beard….

But that’s not just one moment in time, he has apparently always been passionately eccentric …

…His family buried their dead pets in one spot and put the burial markers in another, so that he wouldn’t dig up the corpses; he found them anyway. He froze dead lizards in ice-cube trays, which his mother would discover when she had friends over for iced tea….

…In high school, during the summer and on weekends, DePalma collected fossils, made dinosaur models, and mounted skeletons for the Graves Museum of Archaeology and Natural History, in Dania Beach….

…Typically, paleontologists cede the curation and the care of their specimens to the institutions that hold them, But DePalma insists on contractual clauses that give him oversight of the management of his specimens….

This is a huge Find

For DePalma, it is of course huge, but it is all far bigger than just his career. A new window into the impact event has opened. His thesis adviser estimates that the site will keep specialists busy for half a century …

“Robert’s got so much stuff that’s unheard of,” he said. “It will be in the textbooks.”

This discovery greatly expands our knowledge of the Chicxulub impact’s damaging effects and the far-reaching scope of it. The highly probable link between impact-induced seismic shaking and the onshore inundation surge at Tanis, the location of the find in North Dakota, reveals an important additional mechanism by which the Chicxulub impact could have caused catastrophic conditions in the Western Interior, and possibly worldwide, far from the impact site.

He has now published the first of many studies. This one has identified a potential additional mechanism for abrupt, extensive damage to widely spaced regions and ecologies. The global extinction event, therefore, could have had a rapidly delivered precursor, both at the local and global scales, minutes after impact.

It is an unfolding story of how suddenly 99.9999% of living things died, and over 75% of all species ceased to be on our planet.

Further Reading

The New Yorker article is well worth reading. Published on 29th March 2019, it paints a portrait of both the discovery and DePalma himself.