K-T extinction event, artwork. This catastrophic asteroid impact, which took place 65 million years ago, marked the boundary between the Cretaceous (K) and Tertiary (T) periods. It is thought that the impact contributed to the extinction of the dinosaurs. Here, a large Tylosaurus marine reptile, an example of a tylosaur, is about to be destroyed by the shockwave from the impact. The scene depicted here is in a lagoon in Texas, USA. The impact occurred hundreds of kilometres to the south, off Mexico's Yucatan peninsula. Rising ejecta from the impact is looming over the horizon.