Fossil evidence found in what is now North Dakota has led researchers to believe the fatal asteroid impact wiping out the dinosaurs occurred in the spring, according to a study published in Nature.

New fossil evidence: The Tanis event deposit is home to a unique fossil site that has given researchers new information concerning the extinction of dinosaurs.

  • Unique fish fossils were found in the North Dakota site of the Tanis deposit. Evidence from the fossils holds proof that the Chicxulub asteroid — which is responsible for the mass extinction on the planet in the Cretaceous-Palaeogene periods — impacted Earth in the springtime.

The evidence that led scientists to a conclusion of a springtime catastrophe:

  • The fish fossils found in the ancient river bed are those of fish that died within an hour of the asteroid impact, according to National Geographic. The information in their fossils captured a picture that gives researchers an insight into what happened when the asteroid struck the earth.
  • Upon examination of the paddlefish, the carbon-13 content in their bones was on an incline but had not peaked as it does in the summer. This evidence points to a likely springtime death, the researchers said in Nature.
  • The fish examined in the study are plankton-feeding paddlefish. The plankton they feed on are more active in the spring and summer, which is a time when plankton becomes more active. The levels of carbon-13 in their bodies increased at the time.
  • The growth patterns in the fish bones show that they died during a period of growth, when food and other resources were abundant. When food is plentiful, the bone structure of paddlefish is spongey and porous, as opposed to solid layers of bone mass that occur during the winter, according to the Nature study.
  • The fish found in the Tanis deposit had spongey bone layers, another factor that researchers attribute to death in the spring, according to National Geographic.

How was this data gathered?: The fish bones were studied in the European Synchrotron Radiation Facility in Grenoble, France, using a particle accelerator that makes the world’s brightest X-rays. The high-tech X-rays are what enabled researchers to meticulously inspect the fossils and gather data, according to the facility.