Scientists Announce The Discovery Of The First Dinosaur Likely Killed By The End-Cretaceous Asteroid Impact

Scientists have uncovered what they believe is the first dinosaur fossil directly linked to the end-Cretaceous asteroid impact 66 million years ago, reports.

Very few dinosaur fossils have been found in rocks predating the end-Cretaceous mass extinction. So the announcements of the discovery of a partially preserved leg of a Thescelosaurus at the Tanis site, a fossil lagerstätte dating to the very same day when a 10-kilometer wide asteroid hit Earth, is quite extraordinary. The animal was likely killed and entombed by a tsunami following the asteroid’s impact in what is now the Gulf of Mexico. The waves traveled more than 3,000 kilometers, burying the dinosaur under a layer of rock debris and impact ejecta, together with remains of plants and marine organisms.

The Tanis research site in North Dakota is part of the fossil-rich Hell Creek Formation and one of the most complete Cretaceous-Paleogene boundary (KPg) sites in the world.

A research team led by University of Manchester PhD student Robert DePalma is excavating the site since 2019.

Using multiple lines of evidence, including radiometric dating, stratigraphy, fossilized remains of land and sea animals mixed together, and a distinctive capping layer of iridium-rich clay, in team proposed that the Tanis site contains an impact-caused vertebrate mass-death assemblage dating within the first hours of the end-Cretaceous impact. The asteroid impact led to the extinction of 75 percent of species living on Earth at the time, including all non-avian dinosaurs.

A series of massive tsunami waves, associated with vast earthquakes triggered by the impact, was the cause for the rapidly deposited sediments that locked-in the evidence used in this study.

The dinosaur leg is “stunningly preserved,” as Prof. Paul Barrett from London’s Natural History Museum notes, partially mummified and showing a cast of the scaly skin on the rock’s surface. Based on the small size of the fossil and proportions of the bones, the leg likely belonged to a Thescelosaurus. Thescelosaurus was a genus of bipedal plant-eating dinosaurs that appeared at the very end of the Late Cretaceous period in North America.

“This looks like an animal whose leg has simply been ripped off really quickly. There’s no evidence on the leg of disease, there are no obvious pathologies, there’s no trace of the leg being scavenged, such as bite marks or bits of it that are missing. So, the best idea that we have is that this is an animal that died more or less instantaneously,” so Barrett in the BBC interview.

The BBC documented the discoveries made at Tanis for a documentary hosted by Sir David Attenborough and appropriately named “Dinosaurs: The Final Day” to be aired later in the year.

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