One of the biggest questions that has long been asked about dinosaurs is how did they go extinct? Dinosaurs reigned as the dominant lands animals for the majority of the Mesozoic Era, then suddenly, around 66 million years ago, they vanished from the face of the earth. Different theories about the dinosaurs extinction have been formulated throughout the years, from a terrible disease to catastrophic volcanic eruptions, but no doubt the most popular and one of the most widely excepted theory's is that an asteroid measuring about 10 kilometers (6.2 miles) in diameter collided with earth, forming a crater estimated to be 110 miles in diameter and 12 miles deep in what is now the Gulf of Mexico, triggering immense earthquakes, volcanic eruptions, and tsunamis that may have reached as high as 5,000 feet into the air.
Along with the Chicxulub crater in the Gulf of Mexico, scientists have discovered that the sedimentary layers that mark the boundary between the Cretaceous and the Paleogene (K-PG boundary) all around the world contain a very high concentration of iridium, a rare chemical on earth, but abundant in most asteroids and comets. The clay in the boundary has also been traced to the Chicxulub crater, and giant tsunami beds have been identified in the Gulf Coast and Caribbean. All of this is compelling hardcore evidence, but no remains of dinosaurs or other Mesozoic animals presumed killed by the aftermath of such an impact have been found... that is, perhaps, until now.
Last week, researchers who have been excavating the Tanis fossil site in North Dakota presented their discoveries to the scientific world. Among these discoveries is a mummified leg of a Thescelosaurus, a bipedal herbivorous dinosaur, “stunningly preserved,” said Prof. Paul Barrett of London's Natural History Museum. The leg preserves the scaly skin, and shows no sign of disease or pathologies, nor does it appear to have been scavenged. Instead, it appears to have been buried instantaneously. But what killed it? Perhaps... a tsunami... triggered by the impact of a 10 kilometer asteroid slamming into a shallow sea that would someday become the Gulf of Mexico? The researchers think so.
The Tanis site is a prehistoric graveyard, and one of the most complete K-PG boundary sites in the world. It preserves land and aquatic animals mixed together, and among the Thescelosaurus leg, a pterosaur embryo, skin from a Triceratops, and fish that appear to have breathed in impact debris, as well as what might be a piece of the asteroid itself. A chaotic assemblage that the researchers think was laid down on the exact day, 66 million years ago, that the asteroid struck earth. The Tanis site is about 2,000 miles away from the Chicxulub crater, demonstrating the cataclysmic, nuclear-force affect of the impact, which would have thrown the world into a global winter, ultimately killing an estimated 75 percent of all species on planet earth, including... the dinosaurs.
The BBC News report: