It’s a dinosaur leg, but not just any dinosaur. It was excavated in North Dakota. The fossil holds a story that must have been one of terror. It is the leg of the dinosaur that was killed by the asteroid that made these animals extinct.
There are few fossils that record even the last few thousand years before the impact, which occurred 66 million years ago. The site is called Tanis. It has fossils of other animals that breathed the debris from the impact. There is a fossil turtle that was skewered with a wooden stake. Also, remains of small mammals and the burrows they made. The skin of a horned triceratops and the embryo of a flying pterosaur inside its egg were found. Something else: a fragment of the asteroid impactor itself.
“You look at the rock column, the fossils there, and it brings you back to that day.” Says Robert DePalma, a graduate student at the University of Manchester. The 12 km wide rock hit our planet to cause the last mass extinction. The impact site has been identified in the Gulf of Mexico, off the Yucatan Peninsula.
The remains of Tanis animals and plants were washed into a sediment dump by waves of river water. Aquatic organisms mingle with terrestrial creatures.
The dinosaur killed by the asteroid was not alone. The sturgeon and paddlefish in this tangle of fossils are key. They have tiny particles trapped in their gills. They are the molten rock spheres ejected by the impact that then fell all over the planet. The fish would have breathed in the particles as they entered the river.
In preserved tree resin there are also small inclusions that imply an extraterrestrial origin.
“We were able to separate the chemistry and identify the composition of that material. All the evidence, all the chemical data from that study suggests something clear. We’re looking at a part of the impactor; of the asteroid that wiped out the dinosaurs.”