What happened at the end of the mesozoic era but did not happen at the end of the paleozoic era?

At the end of the Mesozoic Era there was a mass extinction of the species, which was probably caused by an asteroid that fell in the Gulf of Mexico. This did not marked the end of the Paleozoic Era, which ended with the biggest mass extinction of the species ever, but it was caused by super volcanic activities, not an object that came in from the space.